EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, thalloid, with single-celled apical meristem, showing gravitropism; rhizoids +, unicellular; flavonoids + [absorbtion of UV radiation]; chloroplasts lacking pyrenoids; protoplasm dessication tolerant [plant poikilohydric]; cuticle +; cell walls with (1->4)-ß-D-glucans [xyloglucans], lignin +; several chloroplasts per cell; glycolate metabolism in leaf peroxisomes [glyoxysomes]; centrioles in vegetative cells 0, metaphase spindle anastral, predictive preprophase band of microtubules, phragmoplast + [cell wall deposition spreading from around the spindle fibres], plasmodesmata +; antheridia and archegonia jacketed, stalked; spermatogenous cells monoplastidic, centrioles develop de novo, associated with basal bodies of flagellae, multilayered structure +, proximal end of basal bodies lacking symmetry, stellate pattern associated with doublet tubules of transition zone; spermatozoids with a left-handed coil; male gametes with 2 lateral flagellae; oogamy; diploid embryo initially surrounded by haploid gametophytic tissue, plane of first division horizontal [with respect to long axis of archegonium/embryo sac], suspensor/foot +, cell walls with nacreous thickenings; sporophyte multicellular, with at least transient apical cell [?level], sporangium +, single, dehiscence longitudinal; meiosis sporic, monoplastidic, microtubule organizing centre associated with plastid, cytokinesis simultaneous, preceding nuclear division, sporocytes 4-lobed, with a quadripolar microtubule system; spores in tetrads, sporopollenin in the spore wall, wall with several trilamellar layers [white-line centred layers, i.e. walls multilamellate]; close association between the trnLUAA and trnFGAA genes on the chloroplast genome.
Many of the bolded characters in the characterization above are apomorphies of subsets of streptophytes along the lineage leading to the embryophytes, not apomorphies of crown-group embryophytes per se.
All groups below are crown groups, nearly all are extant; characters mentioned are those of the common ancestor of the group.
Abscisic acid, ?D-methionine +; sporangium with seta, seta developing from basal meristem [between epibasal and hypobasal cells], sporangial columella + [developing from endothecial cells]; stomata +, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; underlying similarities in the development of conducting tissue and in rhizoids/root hairs; spores trilete; polar transport of auxins and class 1 KNOX genes expressed in the sporangium alone; MIKC, MI*K*C* and class 1 and 2 KNOX genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns.
[Anthocerophyta + Polysporangiophyta]: archegonia embedded/sunken in the gametophyte; sporophyte long-lived, chlorophyllous, nutritionally largely independent of the gametophyte; sporophyte-gametophyte junction interdigitate, sporophyte cells showing rhizoid-like behaviour.
Sporophyte well developed, branched, free living, sporangia several; spore walls not multilamellate [?here]; apical meristem +.
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Photosynthetic red light response; water content of protoplasm relatively stable [plant homoiohydric]; control of leaf hydration passive; (condensed or nonhydrolyzable tannins/proanthocyanidins +); sporophyte with basipetal polar auxin transport; vascular tissue +, sieve cells + [nucleus degenerating], tracheids +, in both protoxylem and metaxylem; endodermis +; root xylem exarch [development centripetal]; stem with an apical cell; branching dichotomous; leaves spirally arranged, blades with mean venation density 1.8 mm/mm2 [to 5 mm/mm2]; sporangia adaxial on the sporophyll, derived from periclinal divisions of several epidermal cells, wall multilayered [eusporangium]; columella 0; tapetum glandular; gametophytes exosporic, green, photosynthetic; stellate pattern split between doublet and triplet regions of transition zone; placenta with single layer of transfer cells in both sporophytic and gametophytic generations, embryonic axis not straight [root lateral with respect to the longitudinal axis; plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Branching ± monopodial; lateral roots +, endogenous, root apex multicellular, root cap +; tracheids with scalariform-bordered pits; leaves with apical/marginal growth, venation development basipetal, growth determinate; sporangia borne in pairs and grouped in terminal trusses, dehiscence longitudinal, a single slit; cells polyplastidic, microtubule organizing centres not associated with plastids, diffuse, perinuclear; male gametes multiflagellate, basal bodies staggered, blepharoplasts paired; chloroplast long single copy ca 30kb inversion [from psbM to ycf2].
Plant woody; lateral root origin from the pericycle; branching lateral, meristems axillary; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
EXTANT SEED PLANTS / SPERMATOPHYTA
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins derived from (some) sinapyl and particularly coniferyl alcohols [hence with p-hydroxyphenyl and guaiacyl lignin units, so no Maüle reaction]; root stele with xylem and phloem originating on alternate radii, not medullated [no pith], cork cambium deep seated; arbuscular mycorrhizae +; shoot apical meristem interface specific plasmodesmatal network; stem with vascular cylinder around central pith [eustele], phloem abaxial [ectophloic], endodermis 0, xylem endarch [development centrifugal]; wood homoxylous, tracheids and rays alone, tracheid/tracheid pits circular, bordered; mature sieve tube/cell lacking functioning nucleus, sieve tube plastids with starch grains; phloem fibres +; stem cork cambium superficial; branches exogenous; leaves with single trace from vascular sympodium [nodes 1:1]; stomatal pore with active opening in response to leaf hydration, control by abscisic acid, metabolic regulation of water use efficiency, etc.; leaves with petiole and lamina, development basipetal, blade simple; axillary buds +, (not associated with all leaves); prophylls two, lateral; plant heterosporous, sporangia borne on sporophylls; microsporophylls aggregated in indeterminate cones/strobili; true pollen +, grains mono[ana]sulcate, exine and intine homogeneous; ovules unitegmic, parietal tissue 2+ cells across, megaspore tetrad linear, functional megaspore single, chalazal, lacking sporopollenin, megasporangium indehiscent; pollen grains landing on ovule; male gametophyte development initially endosporic, lacking chlorophyll, tube developing from distal end of grain, gametes two, developing after pollination, with cell walls; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; embryo cellular ab initio, endoscopic, plane of first cleavage of zygote transverse, suspensor +, short-minute, embryonic axis straight [shoot and root at opposite ends; plant allorhizic], white, cotyledons 2; plastid transmission maternal; ycf2 gene in inverted repeat, whole nuclear genome duplication [zeta duplication], two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], nrDNA with 5.8S and 5S rDNA in separate clusters; mitochondrial nad1 intron 2 and coxIIi3 intron and trans-spliced introns present.
ANGIOSPERMAE / MAGNOLIOPHYTA
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], S [syringyl] lignin units common [positive Maüle reaction - syringyl:guaiacyl ratio more than 2-2.5:1], and hemicelluloses as xyloglucans; root apical meristem intermediate-open; root vascular tissue oligarch [di- to pentarch], lateral roots arise opposite or immediately to the side of [when diarch] xylem poles; origin of epidermis with no clear pattern [probably from inner layer of root cap], trichoblasts [differentiated root hair-forming cells] 0, exodermis +; shoot apex with tunica-corpus construction, tunica 2-layered; reaction wood ?, associated gelatinous fibres [g-fibres] with innermost layer of secondary cell wall rich in cellulose and poor in lignin; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, wood parenchyma +; sieve tubes enucleate, sieve plate with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, cytoplasm not occluding pores of sieve plate, companion cell and sieve tube from same mother cell; sugar transport in phloem passive; nodes 1:?; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule, reduction in stomatal conductance to increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, overall growth ± diffuse, venation hierarchical-reticulate, secondary veins pinnate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic, parts spiral [esp. the A], free, numbers unstable, development in general centripetal; P +, members each with a single trace, outer members not sharply differentiated from the others, not enclosing the floral bud; A many, filament not sharply distinguished from anther, stout, broad, with a single trace, anther introrse, tetrasporangiate, sporangia in two groups of two [dithecal], ± embedded in the filament, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally, endothecium +, endothecial cells elongated at right angles to long axis of anther; (tapetum glandular), cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine +, thin, compact, lamellate only in the apertural regions; nectary 0; carpels present, superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus short, hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry [not secretory]; ovules few [?1]/carpel, marginal, anatropous, bitegmic, micropyle endostomal, outer integument 2-3 cells across, often largely subdermal in origin, inner integument 2-3 cells across, often dermal in origin, parietal tissue 1-3 cells across [crassinucellate], nucellar cap?; megasporocyte single, hypodermal, functional megaspore, chalazal, lacking cuticle; female gametophyte four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; supra-stylar extra-gynoecial compitum +; ovule not increasing in size between pollination and fertilization; pollen grains landing on stigma, bicellular at dispersal, mature male gametophyte tricellular, germinating in less than 3 hours, pollination siphonogamous, tube elongated, growing between cells, growth rate (20-)80-20,000 µm/hour, apex of pectins, wall with callose, lumen with callose plugs, penetration of ovules via micropyle [porogamous], whole process takes ca 18 hours, distance to first ovule 1.1-2.1 mm; male gametes lacking cell walls, flagellae 0, double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; seed exotestal, much larger than ovule at time of fertilization; endosperm diploid, cellular, heteropolar [micropylar and chalazal domains develop differently, first division oblique, micropylar end initially with a single large cell, divisions uniseriate, chalazal cell smaller, divisions in several planes], copious, oily and/or proteinaceous; dark reversal Pfr → Pr; Arabidopsis-type telomeres [(TTTAGGG)n]; 2C genome size 1-8.2 pg [1 pg = 109 base pairs], whole nuclear genome duplication [epsilon duplication]; protoplasm dessication tolerant [plant poikilohydric]; ndhB gene 21 codons enlarged at the 5' end, single copy of LEAFY and RPB2 gene, knox genes extensively duplicated [A1-A4], AP1/FUL gene, paleo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and three copies of the PHY gene, [PHYB [PHYA + PHYC]].
[NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]]: wood fibres +; axial parenchyma diffuse or diffuse-in-aggregates; pollen monosulcate [anasulcate], tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.
[AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood +; tectum reticulate; anther wall with outer secondary parietal cell layer dividing; carpels plicate; nucellar cap + [character lost where in eudicots?]; 12BP [4 amino acids] deletion in P1 gene.
[[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]] / MESANGIOSPERMAE: benzylisoquinoline alkaloids +; sesquiterpene synthase subfamily a [TPS-a] [?level], polyacetate derived anthraquinones + [?level]; outer epidermal walls of root elongation zone with cellulose fibrils oriented transverse to root axis; P more or less whorled, 3-merous [possible position]; pollen tube growth intra-gynoecial; embryo sac bipolar, 8 nucleate, antipodal cells persisting; endosperm triploid.
[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (extra-floral nectaries +); (veins in lamina often 7-17 mm/mm2 or more [mean for eudicots 8.0]); (stamens opposite [two whorls of] P); (pollen tube growth fast).
[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0.
EUDICOTS: (Myricetin, delphinidin +), asarone 0 [unknown in some groups, + in some asterids]; root epidermis derived from root cap [?Buxaceae, etc.]; (vessel elements with simple perforation plates in primary xylem); nodes 3:3; stomata anomocytic; flowers (dimerous), cyclic; K/outer P members with three traces, ("C" +, with a single trace); A few, (polyandry widespread, initial primordia 5, 10, or ring, ± centrifugal), filaments fairly slender, anthers basifixed; microsporogenesis simultaneous, pollen tricolpate, apertures in pairs at six points of the young tetrad [Fischer's rule], cleavage centripetal, wall with endexine; G with complete postgenital fusion, stylulus/style solid [?here]; seed coat?
[PROTEALES [TROCHODENDRALES [BUXALES + CORE EUDICOTS]]]: (axial/receptacular nectary +).
[TROCHODENDRALES [BUXALES + CORE EUDICOTS]]: benzylisoquinoline alkaloids 0; euAP3 + TM6 genes [duplication of paleoAP3 gene: B class], mitochondrial rps2 gene lost.
[BUXALES + CORE EUDICOTS]: ?
CORE EUDICOTS / GUNNERIDAE: (ellagic and gallic acids +); leaf margins serrate; compitum + [one place]; micropyle?; whole nuclear genome duplication [palaeohexaploidy, gamma triplication], PI-dB motif +, small deletion in the 18S ribosomal DNA common.
[ROSIDS ET AL. + ASTERIDS ET AL.] / PENTAPETALAE: root apical meristem closed; (cyanogenesis also via [iso]leucine, valine and phenylalanine pathways); flowers rather stereotyped: 5-merous, parts whorled; P = calyx + corolla, the calyx enclosing the flower in bud, sepals with three or more traces, petals with a single trace; stamens = 2x K/C, in two whorls, internal/adaxial to the corolla whorl, alternating, (numerous, but then usually fasciculate and/or centrifugal); pollen tricolporate; G , G  also common, when [G 2], carpels superposed, compitum +, placentation axile, style +, stigma not decurrent; endosperm nuclear; fruit dry, dehiscent, loculicidal [when a capsule]; RNase-based gametophytic incompatibility system present; floral nectaries with CRABSCLAW expression.
[SANTALALES [BERBERIDOPSIDALES [CARYOPHYLLALES + ASTERIDS]]] / ASTERIDS ET AL. / SUPERASTERIDAE: ?
Age. Moore et al. (2010: 95% highest posterior density) suggested ages of (107-)103(-98) m.y. for this clade, Naumann et al. (2013) an age of around 109.7 m.y. (but note position of Berberidopsidales - 112.6 m.y.).
Although Soltis et al. (2008) give the ages of divergence of a number of branches below asterids, they are based on a topology [Berberidopsidales [[Caryophyllales + Dilleniales], Santalales, asterids]], and the ages of (131-)120, 117(-112) m.y. in Bell et al. (2010) are based on a similar topology.
Phylogeny. Prior to the seventh version of this site asterids were part of a major polytomy that included rosids, Berberidopsidales, Santalales, and Caryophyllales. However, the study by Moore et al. (2008, esp. 2010) using whole chloroplast genomes with moderately good sampling bids may have cleared up this confusion. Nevertheless, the order of branching below the asterids is still somewhat unstable (e.g. Soltis et al. 2011). For further discussion, see the Dilleniales page.
SANTALALES Berchtold & J. Presl Main Tree.
Mycorrhizae absent; polyacetylenes, e.g. santalbic acid, [triglycerides with C18 acteylenic acids], triterpenic sapogenins + [Loranthaceae?]; cork subepidermal; vessel elements with scalariform perforation plates [E]; perforation plates not bordered; intervascular pits alternate; axial parenchyma strands ³7 cells wide [E], rhombic crystals in ray cells [E]; tension wood?; nodes 3:3 [E]; pericyclic fibres 0; (cristarque cells +); petiole bundle annular [E], (cuticle waxes with annular rodlets, palmone common); petiole/mesophyll with (astro)sclereids; lamina margins entire; inflorescences cymose; flowers quite small [10> mm across], K small, open, cupular, teeth ± inconspicuous, C valvate, large and protecting bud, with adaxial hairs; A opposite C, anthers basifixed; nectary [sometimes as "disc"] +; G , style +, stigma small; ovule 1/carpel, pendulous, apotropous, tenuinucellate, outer and inner integuments ca 4 cells across, (unitegmic), micropyle endostomal; embryo sac curved, with chalazal caecum [?here]; fruit a drupe, 1-seeded, K persistent; seed coat crushed; chalazal endosperm haustoria +, embryo minute, green. - 13 families, 151 genera, 1992 species.
Age. Anderson et al. (2005) date crown-group Santalales at 108-101 m.y.. ?Moore et al. (2010) dated them to (99-)96(-91) m.y.a.. [Check.]
Note: Possible apomorphies are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned is unclear. This is partly because many characters show considerable homoplasy, in addition, basic information for all too many is very incomplete, frequently coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there is the not-so-trivial issue of how ancestral states are reconstructed (see above).
Evolution. Divergence & Distribution. Santalales are unusual in that the parasitic clade it contains is much more diverse than its free-living sister group, the reverse of the size relationship normal in parasitic:non-parasitic clades, however, most Santalales are only hemiparasitic (Hardy & Cook 2012).
Where a number of characters are to be placed on the tree is unclear. Those with an "[E]" after them are found in the first three families below; if these form a single clade, their optimisation will need to be adjusted accordingly.
Ecology & Physiology. The plesiomorphic life style in the clade is to be free-living, and hemiparasitism by attachment to the roots of the host is derived (Malécot 2002; Malécot et al. 2004; Nickrent et al. 2010). Aerial hemiparasitism has been derived some five times (Nickrent 2002), intermediate taxa being both root and stem parasites (Vidal-Russell & Nickrent 2008); photosynthesis in some aerial hemiparasites occurs largely in their stems. Aerial hemiparasites may have a single point of attachment to their host, or roots running over the surface of the bark may form both additional points of attachment and additional plantlets (as in Loranthaceae: Vidal-Russell & Nickrent 2006, 2008). Some Santalales are largely endophytic, even if the part of the plant that is visible is chlorophyllous (Santalaceae, e.g. some species of Viscum and Arceuthobium), while Balanophoraceae are holoparasitic (Nickrent et al. 2005). A few Loranthaceae are hyperparasites, parasitizing other members of that family, and some species of Phoradendron (Santalaceae) are even obligate parasites on other members of the same genus (Calvin & Wilson 2009). For some information on the physiological details of parasitism in Santalales, see Stewart and Press (1990).
Plant-Animal Interactions. Caterpillars of some Pieridae-Pierinae (ca 440 species recorded, but on only 9+ genera; 2/5 of all host-plant records) and Lycaenidae-Lycaeninae-Iolaini in particular are found on members of this order, Loranthaceae (especially), Olacaceae, Ximeniaceae (all Lycaeninae in particular), Opiliaceae and Santalaceae also being recorded as hosts (Ehrlich & Raven 1964; Fiedler 1991, 1995, 1996; Congdon & Bampton 2000), interestingly, cryptic species of mistletoe have higher concentrations of nitrogen than do non-cryptic species (Fiedler 1996). The ancestors of the pierine butterflies seem to have eaten mostly species of Brassicales and their initial santalalean hosts may have been Loranthaceae; there are no reports of pierine caterpillars on free-living Santalales (Braby 2005; Braby & Trueman 2006; Braby et al. 2006: I thank M. F. Braby for information). Interestingly, a number of the adults of these pierines have warning colourations on the undersides of the wings, and some caterpillars also have warning colourations. However, it is unclear what compounds the insects might pick up from their santalalean hosts that would discomfit potential predators (Braby & Trueman 2006), although there is movement of alkaloids from host to parasite in both Santalaceae and Loranthaceae (Cabezas et al. 2009).
Bacterial/Fungal Associations. Little is known about mycorrhizae in Santalales, but the few taxa studied largely lack them (Landis et al. 2002), exceptions being Ongokea, Coula and Strombosia (Malécot 2002 for references); the second two genera are not hemiparasitic. The absence of mycorrhizae, as well as that of root hairs which has also been reported for the group (see below), is probably connected with the adoption of the hemiparasitic habit.
Genes & Genomes.The mitochondrial coxII.i3 intron is absent in Comandra, the only member of the order to have been sampled. The rate of change in the nuclear 18s rDNA gene has been greatly accelerated, but that in other nuclear protein-coding genes much less so (Su & Hu 2012),
Chemistry, Morphology, etc. For the distribution of santalbic acid (octadeca-11-trans-en-9-ynoic acid) in this clade, see Aitzetmüller (2012). The absence of root hairs may be a synapomorphy (Judd & Olmstead 2004), but I do not know if they are absent in the free-living taxa. Vascular pits are notably variously bordered throughout the order (Herendeen et al. 1999b); Carlquist (2006) suggests that non-bordered perforation plates are a possible similarity with Caryophyllales. The foliar vascular bundles may lack fibers (but c.f. Olacaceae, Loranthaceae, ?some Opiliaceae). Terminal tracheids and cristarque cells are scattered, but their exact position on the tree is unclear (Baas et al. 1982; Kuijt & Lye 2005). Wax tubules with palmitone as the main wax occur in several members (Ditsch & Barthlott 1997).
There is some controversy over the morphology of the flower. What appears to be the outer perianth whorl - often a minute, rim-like structure - has been interpreted as being a caylculus of paired and prophyllar/bracteolar origin in a number of Santalales (Wanntorp & Ronse De Craene 2009; Ronse de Craene 2010; Ronse de Craene & Brockington 2013). Such a calyculus might be a fairly high level apomorphy in the order. However, the shift of the bracteoles on to the top of an inferior ovary needs explanation, as does their presence in the terminal flower of a cymule since these would not normally be expected to have any prophylls at all associated directly with them. Finally, in Loranthaceae, a calyculus is described in flowers which are also shown as having a prophyll (Wanntorp & Ronse De Craene 2009). That being said, the calyx in Santalum and Loranthaceae like Struthanthus is unusual in that it initially does not completely encircle the flower, there being an interruption on the adaxial side. Furthermore, Johri and Bhatnagar (1971) note that this structure is not regularly lobed and usually lacks a vascular supply, although it is vascularized in Nuytsia, at least. Finally, in Santalaceae like Comandra there is absolutely no evidence of any calyx, as least from gross morphology. It is best to call any "calyculus", a calyx (see also Kuijt 2013). However, there are still some problems to resolve. Thus the structures called prophylls by Kuijt (2013) and found on vegetative shoots, as in Arceuthobium azoricum, are probably colleters or something similar, since the axillary branches have their first pair of leaves in the same plane as these putative prophylls. The single perianth whorl found in some Santalales represents the corolla of other members (Wanntorp & Ronse De Craene 2009; Ronse de Craene & Brockington 2013), however, at least sometimes its members are reported to have three vascular traces, two coming from commissural bundles (Smith & Smith 1943). Interestingly, the vasculature of the inferior ovary of Darbya (= Nestronia, Santalaceae) and other members of the order suggests that they have become inferior by investment of tissue that is axial in origin (Smith & Smith 1942, 1943; Eyde 1975). Clearly, further developmental studies are much needed.
The corolla haits may be in small tufts where the stamens are inserted on the petals, as in Strombosia and Santalaceae. The anther wall is monocotyledonous in development in Maburea (Erythropalaceae), and there may sometimes be two ovules per carpel (see Maas et al. 1992).
There is considerable discussion as to the number of integuments in "Olacaceae" (e.g. Johri & Bhatnagar 1960, Maas et al. 1992; Breteler et al. 1996; Malécot 2002; summary in Brown et al. 2010 and references), as well as cotyledon number. Tracheids in the nucellus have been reported from some species, as has vascular tissue directly reaching the embryo sac (Werker 1997). Some taxa may have both micropylar endosperm and embryo sac haustoria (Mickesell 1990), and variation in embryo sac morphology, embryo, etc., is also considerable (see e.g. Johri & Bhatnagar 1960).
For information on the first six families in particular, the old Olacaceae, see Reed (1955: general), Baas et al. (1982: leaf anatomy), Sleumer (1984a: New World taxa, pollen, anatomy, etc., 1984b: Malesian taxa, general), Lobreau-Callen (1980, 1982: pollen), and Malécot et al. (2004: general). For other information, see Roberston (1982), Barlow (1997), Calder and Bernhardt (1983), and especially Mathiasen et al. (2008: excellent survey of stem parasitic Santalales); for (poly)acetylenic and related fatty acids in the seeds, see Badami and Patil (1981), for hemi-parasitism, see Fineran (1991) and for chromosome numbers see (Nickrent et al. 2010: supplement). For pretty much everything, see the Parasitic Plants website (Nickrent 1998 onwards) and also Heide-Jørgensen (2008).
Phylogeny. Malécot (2002) analyzed the variation in four genes emphasizing members of the old Olacaceae; he discussed variation of morphological characters in the context of molecular and combined morphological-molecular phylogenies. A number of clades appear to be fairly well supported. Erythropalaceae s.l., including Strombosiaceae and Coulaceae (Coulaceae were not included in all analyses, and their position was rather labile) are perhaps sister to all other Santalales and are free-living (Malécot 2002). These clades tend to differ in most probably plesiomorphic features (e.g. life style) from other Santalales (data from Michaud 1966; Malécot 2002; Malécot et al. 2004: a morphological analysis). However, exactly where they should be placed on the tree still waits for a strongly-supported resolution of relationships within Santalales. Malécot et al. (2004) found some support for Erythropalaceae, Ximenia plus some other genera, and most of the rest of the old Olacaceae (a very weakly supported clade) as three clades successively sister to the rest of Olacales in a morphological analysis. Malécot and Nickrent (2008) since found that the old Olacaceae formed about eight clades basal to other Santalales, but relationships between these clades were unclear (Nickrent et al. 2010: see the tree below).
Within the Loranthaceae et al. clade, Misodendraceae are often sister to [Schoepfiaceae + Loranthaceae], especially in analyses that include many taxa, although when the number of taxa is reduced they may be sister to Schoepfia in particular (Malécot 2002, see also Nickrent et al. 1998; especially Der & Nickrent 2008; Vidal-Russell & Nickrent 2008; Nickrent et al. 2010); this position is followed here. Opiliaceae (one genus) were strongly supported as being sister to a clade [Santalaceae + Viscaceae] in Soltis et al. (2007a; see also Nickrent et al. 2010). Der and Nickrent (2008) found that Santalaceae were polyphyletic, a few genera being placed in Opiliaceae and Schoepfiaceae, while within Santalaceae there are eight well supported clades the relationships of which are for the most part well supported.
Mystropetalum, Dactylanthus, and Hachettia, three members of Balanophoraceae, formed a clade with 100% posterior probability that was sister to a clade with almost 100% support made up of Schoepfia, Dendrophthoe and Santalum, the combined group having 100% support (Nickrent et al. 2005). Thus Balanophoraceae are included in Santalales below, but with no particular position (see also Nickrent 2002; Nickrent & Duff 1996; Barkman et al. 2007); although Nickrent et al. (2005) suggested that Balanophoraceae were to be placed within Santalales, not sister to them, the former position had very little support. Su and Hu (2008, 2011) analysing variation in B-class floral genes and with a quite good taxon sampling suggested that Balanophoraceae were basal or near basal in the clade since they found the euAP3 homologue in Balanophora, but not in other Santalales. Su and Hu (2012) looked at several mostly nuclear genes; relationships were still not clear, but Balanophoraceae certainly seemed to be outside Santalaceae. Balanophoraceae are the only holoparasitic Santalales, and being holoparasitic, they lack most or all of the distinctive vegetative and even floral features of the other mmebers, but they do usually have a bisporic embryo sac and a curved embryo sac (e.g. Fagerlind 1945c, d); the first feature might suggest relationships to Loranthaceae in particular. Further work is needed to resolve details of all these relationships, especially increased sampling in Balanophoraceae.
For additional information on relationships, see Nickrent and Duff (1996) and Nickrent et al. (1998).
Classification. For a classification of all Santalales except Balanophoraceae, see Nickrent et al. (2010). The seven small families for the seven clades of the basal poorly supported pectination are recognised pending resolution of relationships there; if any are sister taxa, they will almost certainly be combined. Families within the old Santalaceae are not recognised, despite the inclusion of highly autapomorphic ex-Viscaceae there.
Previous Relationships. Santalales have often been compared with Icacinaceae (now known to be polyphyletic). Both have a single-seeded fruits, often small calyx, valvate corolla, etc. (e.g. Takhtajan 1997). However, there is little other evidence for such a relationship; for Icacinaceae, see especially Aquifoliales and Garryales.
Includes Aptandraceae, Balanophoraceae, Coulaceae, Erythropalaceae, Loranthaceae, Misodendraceae, Octoknemaceae, Olacaceae, Opiliaceae, Santalaceae, Schoepfiaceae, Strombosiaceae, Ximeniaceae.
Synonymy: Anthobolales Dumortier, Balanophorales Dumortier, Erythropalales van Tieghem, Heisteriales van Tieghem, Loranthales Link, Olacales Martius, Osyridales Link, Viscales Berchtold & J. Presl, Ximeniales van Tieghem - Balanophoranae Reveal, Santalanae Reveal - Loranthopsida Bartling, Santalopsida Brongniart
ERYTHROPALACEAE Miquel, nom. cons. Back to Santalales
Trees, shrubs, or lianes with branch tendrils; laticifers +/0; (vessel elements with simple perforation plates); ground tissue of fibre tracheids; sieve tubes with non-dispersive protein bodies; (nodes 5:5); (epidermal/stomatal cells lignified; with druses), stomata various, cuticular thickening +, large guard cell chamber; leaves spiral or two-ranked, lamina vernation conduplicate, (venation palmate), (petiole pulvinate, margin toothed); inflorescence fasciculate or cymose; flowers (medium-sized; 6-merous); K ± free; C (adaxial hairs 0); stamens = and opposite K or C (with two lateral scales), 2X C; pollen tricolpate or tricolporoidate; (disc 0); G 10-ridged, ± inferior [Erythopalum], opposite sepals (opposite petals) or odd member adaxial, septate (not), style short, stigma ± lobed or not; ovules with micropyle exostomal; fruit 5-valved [Erythropalum], K much accrescent [Heisteria]/not; endosperm with starch or oil, (cotyledons orbicular, foliaceous); n = 16; germination phanerocotylar.
4/40 [list]: Heisteria (30). Pantropical, East Malesia to Talaud and Flores, not Madagascar or East Malesia and to the S.E.; most in Central and South America (map: from Sleumer 1984a, b; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photo - Flower, Fruit.]
Chemistry, Morphology, etc. The laticifers of Heisteria are both articulated and non-articulated (Baas et al. 1982). The stamens differ quite considerably in size, and the smallest stamens are opposite the petals, the largest stamens opposite the sepals (Michaud 1966). The gynoecium is often 10-ridged. A nectary is sometimes present, being described as adnate to the ovary (Sleumer 1984a) or on top of the ovary (Sleumer 1984b; c.f. Nickrent et al. 2010).
For some information on pollen, see Lobreau-Callen (1982). See Maas et al. (1992) for information on Maburea.
Baas et al. (1982: they examined Brachynema ramiflorum) recorded only infrequent and thin-walled sclereids. However, in the material examined there were numerous sclereid nests in the cortex, indeed, they sometimes formed an almost a continuous layer outside the pericycle. Furthermore, stem, petiole, and also, judging from the way young leaves had dried, even the midrib have strongly sclerified diaphragms in the pith; the inside of the xylem cylinder was strongly fluted. Sleumer (1984a, q.v. for stamenoposition, etc.) described the inflorescence as being an ebracteate corymb. The seed coat is almost obliterated, and it is difficult to make out details of cell walls, etc. Sleumer (1984) described the endosperm as having amylum and fatty substances; the endosperm stains rather weakly for starch, and the cells contain yellowish globules, the "fatty" and "sticky" substances below.
Phylogeny. Molecular data place Brachynema, a genus that is so morphologically distinctive that its inclusion in the order was in some doubt (e.g. see versions 7 of this site and earlier), close to Maburea, in Erythropalaceae s. str. (K. Wurdack, pers. comm.); the genus is not mentioned by Nickrent et al. (2010). Nodal anatomy and stomatal morphology, at least, are in agreement with this position. Maas et al. (1992) noted the similarity of Maburea and Brachynema in leaf anatomy.
Previous Relationships. Brachynema has often been associated with "Olacaceae" s.l. (Santalales), thus Lobreau-Callen (1980) placed it in Anacoloseae (Aptandraceae) and Baas et al. (1982) placed it with Scorodocarpus (Strombosiaceae) in particular (see also above). It has also been linked with Ebenaceae (Ericales), as by Reed (1955) and others, while in a morphological phylogenetic analysis it appeared close to Symplocaceae (Ericales; Malécot 2002).
Synonymy: Heisteriaceae van Tieghem
[Strombosiaceae [Coulaceae [Ximeniaceae [Aptandraceae, Olacaceae [Octoknemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]]]]: C ± connate; A adnate to C.
STROMBOSIACEAE van Tieghem Back to Santalales
(Mycorrhizae +); ?santalbic acid; (vessel elements with simple perforation plates); ground tissue of libriform fibres; (nodes 1:1, 5:5); (petiole bundle with adaxial bundles); (groups of very narrow fibres associated with foliar vascular bundles); epidermal cells crystalliferous, with silica sand, stomata aniso-, cylco-, (helico)cytic; leaves spiral to 2-ranked, (lamina venation palmate); inflorescence fasciculate; flowers 4-5 merous, (hypanthium +), (C fleshy); (nectary extrastaminal - Engogemona); A = and opposite C, 10, (filaments short, connective massive, anthers transversely multiseptate - Tetrastylidium), (loculi dehiscing separately - Engomegoma); pollen tricolpate/tricolporoidate; G [3-6], (semi-inferior), septate at base, style short to long; ovules also unitegmic, integument ca 6 cells across, micropyle long; (megaspore mother cells several), (embryo sac caecum 0); endosperm starchy, chalazal endosperm haustorium unicellular; n = 20.
6 [list]/18. Scattered Pantropical (map: Sleumer 1984a, b; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). Photo - Fruit.]
Chemistry, Morphology, etc. For general information, see Sleumer (1984a, b); see Agarwal (1963b) for Strombosia and Breteler et al. (1996) for information on Engomegoma.
Synonymy: Scorodocarpaceae van Tieghem, Tetrastylidiaceae van Tieghem
[Coulaceae [Ximeniaceae [Aptandraceae, Olacaceae [Octoknemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]]]: ?
COULACEAE van Tieghem Back to Santalales
(Mycorrhizae +); ?santalbic acid; laticifers +; mesophyll lignified; epidermis lignified, with druses, stomata paracytic, epidermis with cork-warts [from stomatal complexes]; hairs dendritic; lamina venation scalariform; inflorescence spicate; (C adaxial hairs 0); A 10 (15); nectary 0?; G (3-)4-5), style 0-short; ovules bitegmic only, outer and inner integuments 5-6 cells across; endosperm with starch; n = ?
3 [list]/3. Interrupted pantropical (map: Sleumer 1984a, b; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010).
Chemistry, Morphology, etc. For general information, see Sleumer (1984a, b).
[Ximeniaceae [Aptandraceae, Olacaceae [Octoknemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]]: root hemiparasites; vessel elements with simple perforation plates; axial parenchyma strands 7³ cells wide; nodes 1:1; sclerenchyma fibres of petiole and median vein often 0; petiole bundle arcuate; cuticular thickening +, guard cell chamber small, stomata paracytic; silicification of some foliar mesophyll/epidermal cells; ovules unitegmic; embryo sac curved, with chalazal caecum and ± developed micropylar prolongation.
Evolution. Divergence & Distribution. Moore et al. (2010: 95% highest posterior density) suggest ages of (99-)96(-91) m.y. for a clade that includes Ximenia and Phoradendron.
Endress (2011a) thought that the inferior ovary in Santalales might be a key innovation for them. However, it is difficult to assign ovary position to a particular place on the tree. Many taxa in the families above have a superior ovary, and so do [Exocarpos + Omphalomeria], a "basal clade" in Santalaceae (Der & Nickrent 2005), Loranthaceae are inferior, Schoepfiaceae are half inferior, and more or less inferior ovaries are found elsewhere in the clade. Either there are independent origins for the character of inferior ovary, or reversals, or both.
Chemistry, Morphology, etc. Graniferous tracheary elements are found in the haustoria of several unrelated members of the clade; the granules are usually proteinaceous, but are made up of starch in Ximenia (Fineran & Ingerfeld 1982).
Ovule, embryo sac and embryo development of many plants in this clade is more or less remarkable. Distinct ovules may not be recognizable, the embryo sacs being borne in a spherical body, the mamelon; this consists of a basal placenta and everything else (see also Ross & Sumner 2005). Individual embryo sacs may elongate greatly and approach the apex of the mamelon or even the stigma at the end of a long style; Haig (1990) suggests that this may represent competition between female gametes given that their normal spatial constraints (i.e., being enclosed in an organised ovule) are absent. In any event, after fertilization the embryo is "planted" back down at the base of the mamelon by the development of a long suspensor (Fagerlind 1947a, 1948; Maheshwari 1950; Bhatnagar & Johri 1960; Ram 1970; Bhatnagar 1970; Bhandari & Vohra 1983; Johri et al. 1992; Shamrov et al. 2001, and references). Cocucci (1983) outlined variation in ovary morphology and the distribution of starch-containing tissues (primarily in the style or the mamelon); these latter may be involved in the extraordinary growth of the embryo sacs. However, much more work on embryology and gynoecial morphology is needed.
Phylogeny. Details of lamina anatomy largely agree with the circumscription of this clade (Baas et al. 1982).
XIMENIACEAE Horaninow Back to Santalales
(Axillary thorns - Ximenia); rhombic crystals (and silica bodies) in ray cells; ground tissue of fibre tracheids; (stomata anomocytic); (lamina venation palmate); inflorescence ± umbellate; flowers 4-5-merous; A (= and opposite C), 2 (3) x C, (very long - Curupira); nectary 0; style short to long; (ovules unitegmic); cotyledons 2, connate or not; n = 12 (13); germination hypogeal.
4 [list]/13. Pantropical, warm temperate (map: from van Balgooy 1993; Fl. Austral. 8. 1984; Sleumer 1984a, b; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010).
Chemistry, Morphology, etc. Ximenia americana is crassinucellate. Some information is taken from Sleumer (1984a, b: general).
[Aptandraceae, Olacaceae [Octoknemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]]: ovules unitegmic or ategmic.
Phylogeny. There is no strong evidence that this is a clade; I have simply optimized a character to this node.
APTANDRACEAE Miers Back to Santalales
Branches plagiotropic [?many]; (arbuscular mycorrhizae + - Ongokea); laticifers +; rhombic crystals in ray cells; nodes 1:1, 5; (petiole bundle fibres +); (epidermis with cork-warts [from stomatal complexes] - some Aptandra); twigs somewhat zig-zag; leaves 2-ranked; (plant dioecious); flowers 4-5 merous, bracteoles ± connate; (C with apical thickenings); (A connate around style, anthers reflexed - Aptandra), (extrorse), also dehiscing by pores or valvate, (3-valvate in Hondurodendron); (pollen oblate, 6-aperturate, tri-diporate); (nectary 0; outside A [Aptandra]; alternating with A); G [2(-3)]; ovules often bitegmic; K accrescent (fruit surrounded by accrescent disc or adjacent structures; fruit nut-like); (endosperm with starch), cotyledons 0-2, connate or not; n = ?
8 [list]/34: Anacalosa (18). Pantropical (also SE China, Formosa) (map: from Michaud 1966; van Balgooy 1993; Sleumer 1984a, b; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photo - Flower.]
Age. For records of the distinctive breviaxial tri-diporate fossil pollen Anacalosidites, very similar to pollen of Anacalosa, Cathedra, and Phanerodiscus, from the Upper Cretaceous (Europe, Maastrichtian) and Palaeocene and particularly Eocene (worldwide) onwards, see Krutzsch (1988), Malécot (2002), and Malécot and Lobreau-Callen (2005).
Chemistry, Morphology, etc. In the anthers of Chaunochiton (Aptandra clade) each loculus opens by a separate slit. Some information is taken from Sleumer (1984a, b: general); see also Ulloa Ulloa et al. (2010) for the remarkable Hondurodendron.
Phylogeny. There are two easily-characterizable clades within Aptandraceae. The Aptandra clade, with five genera, includes taxa with a more or less extra-staminal nectary, valvate anthers, pollen with concave meso- and apocolpium, and a calyx that is accrescent in fruit, while the Anacalosa clade, with three genera, has lignified guard cells, anthers dehiscing by pores and with prolonged connectives, diploporate pollen, and the disc or extradiscal area is accrescent in fruit (Malécot et al. 2004; Nickrent et al. 2010). Taxa in both clades have petals with apical thickenings.
Synonymy: Cathedraceae van Tieghem, Chaunochitonaceae van Tieghem, Harmandiaceae van Tieghem
OLACACEAE R. Brown, nom. cons. Back to Santalales
SiO2 bodies in ray cells; nodes 1;1, 3; leaves 2-ranked; (flowers heterostylous); (K 0); (C 3 - Olax); A 1-2 x C, [fertile A 3, staminodes 3-6, opp. C (Dulacia)]; pollen grains breviaxial, (tricellular); G ridged or not; ovules ategmic, (unitegmic, integument 5-6 cells across), (nucellar cap + - Olax); embryo sac bisporic [chalazal dyad], eight-celled [Allium-type] - Olax; K much accrescent/not; (chalazal haustorium growing into pedicel - Olax), starch slight, cotyledons 0-1; n = 12.
3 [list]/57: Olax (40). Pantropical (also S.E. China, Formosa) (map: from Sleumer 1984a, b; Fl. Austral. 8. 1984; Malécot 2002; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010).
Evolution. Ecology & Physiology. For the hemiparasitism of Olax phyllanthi, see Tennakoon et al. (1997 and references). Hibberd and Jaeschke (2001) provide a model of nutrient flow between host and parasite.
Chemistry, Morphology, etc. Dulacia is heterostylous. Again the smaller stamens may be opposite the petals, the larger stamens opposite the sepals. Olacoideae are ategmic, and Olax has endosperm haustoria reaching into the pedicel.
Some information is taken from Sleumer (1984a, b: general); for embryology, see Agarwal (1963a).
[Octoknemaceae [[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]]: ?
OCTOKNEMACEAE van Tieghem nom. cons. Back to Santalales
?Santalbic acid; axial parenchyma strands ³7 cells wide; phloem with bundles of fibres; nodes 5:5; petiole bundle annular; no silicification of foliar cells; hairs stellate or dendritic; stomata cyclocytic, anomocytic, etc., cork warts on leaf [from hair bases]; inflorescences branched or not, in fascicles, from endogenous buds; plant dioecious; (flowers 3-merous); staminate flowers: (disc +); pistillode; carpellate flowers: staminodes +; (glands alternating with staminodes); G 3, style short, stigma flap-like, multi-lobed; integuments 2 or 1; fruit drupaceous; seed longitudinally ruminate, radicle relatively very long, cotyledons 6; n = ?
1 [list]/14. Tropical Africa (map: from Gosline & Malécot 2012; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010).
Chemistry, Morphology, etc. For a summary of what is known about this genus, see Gosline and Malécot (2012).
Phylogeny. Molecular data place Octoknema rather differently than do morphological observations, which put the genus with the free-living members of Santalales (e.g. Malécot et al. 2004); if the latter position is confirmed, this may suggest that there have been a number of reversals in habit in this clade.
Classification. For a monograph, see Gosline and Malécot (2012).
[[Loranthaceae [Misodendraceae + Schoepfiaceae]] [Opiliaceae + Santalaceae]]: guard cells not lignified; G not septate; ovules undifferentiated, ategmic; testa 0; endosperm oily, starch 0.
Age. This node was dated to (102-)97, 85(-80) m.y. by Wikström et al. (2001); Bell et al. (2010) suggested an age of (115-)99, 91(-76) m.y. and Magallón and Castillo (2009) suggest ages of ca 90.6 m.y.
Chemistry, Morphology, etc. ?Cristarque cells.
[Loranthaceae [Misodendraceae + Schoepfiaceae]]: ?santalbic acid; cambium storied; petiole astrosclereids 0; guard cell thickenings?; epidermal cells sclerified, with druses; K minute; G .
Age. The age of this clade is perhaps ca 81 m.y. (Vidal-Russell & Nickrent 2008a), while Naumann et al. (2013) estimated that its age was around 67.1 m.y..
LORANTHACEAE Jussieu, nom. cons. Back to Santalales
Ellagic acid +, condensed tannins +; parenchyma apotracheal; cuticular epithelium developing; (stomatal orientation transverse); flowers medium-sized to large (small); pollen oblate, triradiate to triangular, apertures confluent or not; G 3-12 [number sometimes estimated from "ovules"], inferior, placentation basal; ovules 4-12; megaspore mother cells many [archesporium "massive"], embryo sac growing up style (to tip); collenchymatous zone below the embryo sacs +; mesocarp with rubber outside vascular bundles; endosperm composite [derived from several ovules], suspensor long, plane of first cleavage of zygote vertical; n = 12.
68[list]/950 - 2 groups below. ± Tropical.
Age. The family started diversifying only 28-40 m.y.a. (Vidal-Russell & Nickrent 2008a).
1. Nuytsieae van Tieghem
Santalbic acid 0; stomata tranverse to long axis of leaf; leaves spiral; plant monoecious; C 6-8, free, yellow; fruit dry, 3-winged; embryo size?, cotyledons 3-4, foliaceous.
1/1: Nuytsia floribunda. S.W. Australia (map: from FloraBase 2006).
Synonymy: Nuytsiaceae van Tieghem
2. The Rest.
Usu. stem parasites, forming burl at point of attachment and with epicortical roots running over the surface, often forming secondary burls; indumentum quite often complex; leaves opposite (spiral); (plant dioecious); flowers (slit-monosymmetric; opening explosively), (3-)5-6(-9)-merous; calyx usu. unvascularized (vascularized- Atkinsonia); K (0), C (0, 4-7); (A dimorphic [one pair sterile]), (anthers septate); (pollen spherical); (placentation axile - e.g. Lysiana); embryo sac bisporic [chalazal dyad], eight-celled [Allium-type]; fruit also a berry (nut); (endosperm 0), embryo chlorophyllous, ± plug-shaped, medium to long?, (cotyledons connate; to 11 - Psittacanthus); no radicle, primary haustorium +; (germination cryptocotylar); n = (8-11).
67/950: Tapinanthus (250), Psittacanthus (120), Amyema (95), Agelanthus (60), Struthanthus (50), Phthirusa (40). ± Tropical (warm temperate) (map: from Meusel et al. 1965; Jäger 1970; Barlow 1983; Polhill & Weins 1998; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photo - Flower]
Synonymy: Bifariaceae Nakai, Elytranthaceae van Tieghem, Gaiadendraceae Nakai, Psittacanthaceae Nakai
Evolution. Divergence & Distribution. Although Loranthaceae are common in Australia and were, one might have thought, easily dispersed, they are unknown from Tasmania (but are found in New Zealand, etc.).
In Australia, the shapes of loranth leaves and of the eucalyptus host on which they grow are often similar; explanations for this vary and this phenomenon is at most uncommon elsewhere (Barlow & Wiens 1977). Press and Phoenix (2005) discuss interactions of Loranthaceae with their hosts (see also below).
Kuijt (2009b) noted that floral variation in Neotropical Loranthaceae was far greater than in Palaeotropical members. Kuijt (2011) suggested that sessile, axillary, 4-merous flowers were primitive in the family - genera around Phthirusa were examples.
Pollination Biology & Seed Dispersal. Loranthaceae are a major source of nectar and fruit for birds throughout the tropics. There are about 200 species of bird-pollinated Loranthaceae in Africa (Polhill & Wiens 1998), about 70 species in Australia (Barlow 1984), 36 in China (Qiu & Gilbert 2003), 165 in Malesia (Barlow 1998), and 125 in the New World. 44 species in two genera of Nectariniidae-Dicaeidae, flowerpeckers, are endemic to the Indo-Australian area, and they are involved in both pollination and seed dispersal of the family there (e.g. Reid 1983; Docters van Leeuwen 1954). In some taxa the flower will open only if it is pecked by the bird (hence their common name, "flower peckers"); opening is explosive, and the bird gets covered by pollen. Other very common pollinators in the family are the closely related sunbirds (Nectariniidae-Mectariniini), also Old World, and they also pollinate Loranthaceae, perhaps especially species whose flowers do not open explosively, in Malesia (Corlett 2004). They are the main pollinators of the almost African Loranthaceae, and Kirkup (1998) provides a detailed study of the variety of floral morphologies involved. In tropical America humming birds are the major pollinator of the family. Vidal-Russell and Nickrent (2008b) discussed the evolution of bird-pollinated flowers in the family; they thought that bird pollination had evolved several times.
Loranthaceous seeds are also dispersed by birds, defaecation or regurgitation being the two common mechanisms; the behaviour of the disperser is sometimes modified in distinctive ways. The seeds pass through the gut in a mere 20 minutes and are deposited on a branch; germination is almost immediate. The bird sometimes shows distinctive behaviour as it defaecates, swinging its body parallel to the branch so the seed lands on the branch and germinates there (Docters van Leeuwen 1954 in particular; Reid 1983; Godschalk 1983; Polhill & Wiens 1998: African taxa; Restrepo 1987: South American species). The viscid covering of the embryo aids in its attachment to the branches, and sometimes the seeds occur in long, dangling strings, "rosaries" (Restrepo 1987), held together by the viscin. Overall, about 90 species of birds from 10 families are specialists on the fruit of Loranthaceae (and some Santalaceae: see Mathiasen et al. 2008). However, how good mistletoe specialists are in dispersing seed to uninfected trees has been questioned, more generalist fruit-eaters perhaps being better at this (Watson & Rawsthorne 2011).
Plant-Animal Interactions. Loranthaceae are the major hosts for caterpillars of pierid and lycaenid butterflies in Santalales (see introduction to Santalales for literature). Lycaenidae-Iolaini caterpillar preferences show quite a good agreement with the classification of Pohill (1998), in particular, most Iolaini are found either on tapinanthoid or taxilloid genera, the two main African groups of the family (Congdon & Bampton 2000). Caterpillars of the pierid Delias occur on Malesian Loranthaceae (Docters van Leeuwen 1954). Elephants like to eat Loranthus, and will knock over Acacia trees to get at the plant (White 1983: see also Santalaceae-Visceae).
Ecology & Physiology. The root parasitic habit, as in Nuytsia, is probably plesiomorphic in the family, since Nuytsia is sister to the rest of the family (Vidal-Russell & Nickrent 2005) and the most immediate out groups (but not Misodendraceae) are root parasites. Atkinsonia, from S.E. Australia (which has a vascularized "calyx" - see Johri & Bhatnagar 1972), and Gaiadendron, from Central and South America), are two other root parasitic genera that may also be near the base of the phylogeny. Roots of Phrygilanthus acutifolius are described as growing down from the host into the soil, and thence to trees many metres away, which they then parsitize (Benzing 1990). Hence be careful with the characterisation of "the rest" above (Wilson & Calvin 2006a, b; c.f. Vidal-Russell & Nickrent 2008b: support not very strong).
It is estimated that the stem/branch parasitic habit evolved ca 28-40 m.y.a. (Vidal-Russell & Nickrent 2006, 2008a), about when the family started diversifying. In such parasites, the host-parasite junction may be much swollen, producing wood roses - ultimately split and branched cup-shaped vascular tissue - in the host. Morphological details of the association between stem parasite and hosts varies, and the epicortical roots, which may be plesiomorphous in the aerial parasites, form either sympodial or monopodial systems (e.g. Polhill & Weins 1998; Calvin & Wilson 2006; Wilson & Calvin 2006b). Wilson and Calvin (2006a, b) discuss the evolution of the various kinds of host attachments, although given the weak support for relationships at the base of the tree it is premature to worry too much about how many times aerial parasitism has evolved; aerial parasitism may have arisen only once in the family (Vidal-Russell < Nickrent 2008b). Some Loranthaceae are hyperparasites, parasitizing other Loranthaceae, while the endophytic Tristerix aphyllus can almost be considered holoparasitic, only the inflorescence appearing on the cacti it inhabits (Amico et al. 2007; Fisher et al. 2013).
Loranthaceae can be keystone resources whereever they grow - and not simply because they provide snacks for elephants. They are a reliable source of both fruit and nectar for vertebrates, birds in particular, and the dense clumps of stems they form on branches are valued as nest sites by many birds (Watson 2001; Watson & Hering 2012). Fallen leaves, and excreta of organisms associated with the parasite, may enrich soil nutrients in nutrient-poor communities, and increase total biomass, diversity, etc. (Watson 2009; Watson & Hering 2012). In Australia, at least, mistletoe diversity in a community is unconnected with its productivity, but host ranges are narrower in less productive (= less diverse) communities (Kavanaugh & Burns 2012).
Genes & Genomes. Mitochondrial genes from a presumably root-parasitic member of Loranthaceae seem to have been acquired by the fern Botrychium, perhaps via a common mycorrhizal associate (Davis et al. 2005b). However, in general mycorrhizae are not very common in Santalales and if the gene transfer took place in Asia, as Davis et al. (2005b) suggested, the absence of root-parasitic Loranthaceae from that area is notable.
Economic Importance. Mathiasen et al. (2008) provide a list of Loranthaceae that harm crops - citrus and cocoa are particularly susceptible.
Chemistry, Morphology, etc. The calyx-like structure on top of the flower of Struthanthus and Phthirusa is described as a calyculus by Wanntorp and Ronse De Craene (2009), and is thought to be of prophyllar origin - but this is perhaps unlikely (see above). Polysymmetric 6-merous flowers seem to be plesiomorphous in the family (Barlow 1983; Wilson & Calvin 2006), but 7- (or 8-)merous flowers occur in Atkinsonia and Notanthera (see below), the stamens being inserted at two levels on the corolla (Kuijt 2010). The embryo sac in Moquiniella is some 48 mm long, the longest in the angiosperms; it grows up the style and then may grow back downwards after reaching the stigma (this is sometimes called an embryo sac haustorium - see Mikesell 1990), and other members of the family have embryo sacs nearly as long (e.g. Johri & Bhatnagar 1972; Cocucci 1990). Both Cronquist (1981) and Takhtajan (1997) describe the endosperm as being starchy, but it is not so scored in Malécot (2002). In many Old World Loranthaceae the cotyledons are connate, but not basally; the plumule emerges through the basal slit (Kuijt 1969).
For much information about all aspects of the family, see Johri and Bhatnagar (1972), for growth habits, see Benzing (1990), for seedlings of neotropical Loranthaceae, see Kuijt (1982), for foliar anatomy, see Kuijt and Lye (2005: terminal tracheids and cristarque cells common), for pollen, see Feuer and Kuijt (1985 and references), and for embryology, etc., see Raj (1970) and Bhatnagar and Johri (1983).
Phylogeny. Relationships within Loranthaceae are being clarified. Nuytsia is sister to the rest of the family (Vidal-Russell & Nickrent 2005). The root parasitic Atkinsonia (S.E. Australia) and Gaiadendron (Central and South America) may also be near the base of the phylogeny (it has spherical inaperturate pollen), although there is rather weak support for the stem parasite Notanthera being sister to all Loranthaceae except Nuytsia (Wilson & Calvin 2006a, b; c.f. Vidal-Russell & Nickrent 2008b).
Classification. For an account of Nuytsia, see Hopper (2010); for a monograph of Psittacanthus, see Kuijt (2009a), and for a suprageneric classification of the whole family, see Nickrent et al. (2010); for some generic limits, see Kuijt (2011).
Previous Relationships. Loranthaceae and Viscaceae (see Santalaceae below, as Visceae) have often been considered to be close, even being put in a single family, but there are numerous features separating the two; Kuijt (1969), Raj (1970) and Polhill and Wiens (1998) provide useful tables of differences. Thus the viscous covering of the seeds of loranthaceae is mesocarpial in origin, being outside the vascular bundles and, the fruits of Loranthaceae contain rubber and are sometimes used as bird lime. Although some Loranthaceae such as Phthirusa have very small flowers and congested inflorescences, they are easily separated from Visceae which also have these features; plants of the latter are often lighter green in color, they lack roots running over the surface of the host, their flowers are often three merous, and they have green endosperm, etc.
[Misodendraceae + Schoepfiaceae]: pollen 4-colporate.
Age. The age of this node is ca 75 m.y. (Vidal-Russell & Nickrent 2006, 2007).
MISODENDRACEAE J. Agardh, nom. cons. Back to Santalales
Stem parasites; stem apex aborting; bundle fibres +; sieve tube plastids lacking starch and protein inclusions; plant dioecious; inflorescence (compound) raceme or spike; pedicels pubescent; staminate flowers: K/C 0; A 2-3, monothecal; pollen 4-12-colporate, spinuliferous; carpellate flowers: C 3; staminodes alternate with C; ovules straight; fruit dry, attached to 3 much accrescent long plumose staminodes growing from slits in the ovary to one side of the attachment of the C; seed coat with some sclereids; endosperm 0-copious, embryo short to large, cotyledons connate; n = 6, 8; germination epigeal.
1/8. Cool temperate South America (map: from Heywood 1978). [Photos - Misodendron Flower, Misodendron Habit]
Evolution. Ecology & Physiology. Stem parasitism evolved here well before that in Loranthaceae, which occurred some ca 40 m.y.a. (Vidal-Russell & Nickrent 2006, 2007).
Chemistry, Morphology, etc. According to Takhtajan (1997) the pollen is colpate. For general information, see Kuijt (1969), for seeds and seedlings, see Kuijt (1982: corrections to earlier work), and for details of wood anatomy, see Carlquist (1985c).
Phylogeny. For a phylogeny of Misodendron, see Vidal-Russell and Nickrent (2007).
SCHOEPFIACEAE Blume Back to Santalales
(Herbs); aliform confluent parenchyma +; epidermal cells not lignified, (stomata anomo-/cyclocytic); hairs unicellular/0; bract and bracteoles immediately below and surrounding G; (flowers distylous), medium-sized; (K asymmetric [Quinchmalium]), C tubular, with adaxial hairs; pollen tetrahedral, heteropolar, apertures ± confluent, ektexine smooth; G (semi-)inferior, basally septate, stigma lobed to capitate; ovules ategmic/?unitegmic; embryo sac with with synergid haustoria [Quinchamalium]; n = 12, 14.
3 [list]/55: Quinchamalium (25). Central and South America, a few species in tropical South East Asia-West Malesia (map: from Sleumer 1984; South East Asian mainland and South America only approximate distribution). [Quinchamalium flower.]
Chemistry, Morphology, etc. Sleumer (1984) noted that the wood had aliform-confluent parenchyma, unlike other "Olacaceae". There are prominent bracteoles immediately below the flowers which look not unlike those of Loranthaceae, and the calyx and pollen of Schoepfia are also similar to those of Loranthaceae. However, pollen aperture development in Schoepfia follows Garside's Rule, there being three pores at four points in the tetrad (see Blackmore & Barnes 1995) - other genera?
Some information is taken from Smith and Smith (1943: floral morphology) and Dawson (1947: general), but some of the detail in the characterization above refers to Schoepfia alone; the family is very poorly known.
Phylogeny. That Schoepfia is rather different from "Olacaceae" had often been remarked (e.g. Metcalfe & Chalk 1950; Sleumer 1984). Arjona, ex Santalaceae, is sister to Schoepfia (Malécot 2002), and Quinchamalium, another ex Santalaceae, is also to be included here (Smith & Smith 1943 noted relationships between these two genera). Support for the relationships [Schoepfia [Arjona + Quinchmalium]] is strong (Vidal-Russell & Nickrent 2006; Der & Nickrent 2008).
Synonymy: Arjonaceae van Tieghem
[Opiliaceae + Santalaceae]: single perianth whorl only.
Age. Bell et al. (2010) dated this node to (106-)89, 82(-64) m.y.a., while Wikström et al. (2001) suggested an age of (85-)80, 69(-64) m.y..
Chemistry, Morphology, etc. The single perianth whorl - very common in this clade - is probably equivalent to the corolla of other members of the order, where the calyx is often small; Hiepko (1984) called this single whorl the perianth in Opiliaceae only because there was no obvious calyx.
OPILIACEAE Valeton, nom. cons. Back to Santalales
Root parasitic trees or shrubs (lianes); tanniniferous?; wood often fluorescing; nodes 1:(1), 3, 5; mesophyll lacking sclerified cells; cystoliths + (0); stomata paracytic, transversely oriented on the stem [Anthoboleae]; leaves two-ranked to spiral; inflorescences axillary, (catkin-like, with relatively large bracts), (plant dioecious); flowers small, (3-)4-6(-8)-merous; hypanthium + or 0; K very small, C free to ± connate, (in carpellate flower of Gjellerupia 0); A adnate to C or not; pollen usu. colporate, microechinate, triangular; (prominent nectaries alternating with A); G [2-5] (half inferior), placentation free central, style short or 0, stigma ± capitate; (ovules erect, basal - Agonandra); 1(-few) embryo sacs only; (pedicel swollen, coloured - Anthoboleae); secondary endosperm haustoria +; endosperm also oily, embryo narrow, long (rather short), radicle very short, cotyledons (2-)3-4; germination epigeal; n = 10.
11[list]/36. Pantropical (map: from Stauffer 1959; Hiepko 1984, 2000, M. Gustafsson pers. comm. ii.2010 - Africa; FloraBase x.2012; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photo - Flower]
Chemistry, Morphology, etc. Metcalfe and Chalk (1950) describe a branching system of lignified cells connecting veins in Olacaceae s. str., i.e. not including Anthoboleae. Agonandra and Anthoboleae have amphistomatic leaves and green twigs. Stauffer (1959) suggested that there might be viscin in the fruits of some Anthoboleae.
For embryology, see Ram (1970), and for general information, see Stauffer (1959) and Hiepko (1984).
Phylogeny. The Australian Anthobolus, ex Santalaceae, is to be included here - [Lepionurus (support strong) [Anthobolus + The Rest (support weak)]] (Der & Nickrent 2005, esp. 2008), and it, like other Opiliaceae, has a superior ovary. Other Anthoboleae are close to Santalum and relatives (Der & Nickrent 2008: support strong).
Previous Relationships. Stauffer (1959), who monographed Anthoboleae, considered that they were closer to Santalaceae than to Opiliaceae.
Synonymy: Anthobolaceae Dumortier, Cansjeraceae J. Agardh
SANTALACEAE R. Brown, nom. cons. Back to Santalales
Ellagic acid 0; axial parenchyma strands 0; cuticular epithelium common; (cuticle waxes as rodlets); guard cell thickenings unknown; epidermal cells sclerified, with druses; stem stomata transversely oriented; flowers small, (3-)4-5(-8)-merous; hypanthium + or 0; K 0, usually an adaxial patch of hairs on C; large nectary glands often +, alternating with stamens; pollen various; G [2-5], inferior, odd member abaxial, (placentation free central), style hollow [Okoubaka], stigma often capitate or lobed; ovules straight (anatropous), or not distinguishable; fruit [mesocarp stony] also baccate, (outer part exfoliating); endosperm (helobial; green), starchy or not, embryo short to long.
44[list]/990. World-wide, esp. tropics (map: see Meusel et al. 1965; Hawksworth & Wiens 1972; Fl. Austral. 8. 1984; Jalas & Suominen 1976; Polhill & Weins 1998; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photos - Acanthosyris fruit.]
1. Comandra group
Plant herbaceous; (hypanthium +); stigma punctate to subcapitate; ovules anatropous, unitegmic; embryo sac with lateral caecum; secondary endosperm haustoria + [and Mida], plane of first cleavage of zygote vertical; n = 13(14).
2/2. North America, Europe, ± temperate.
Synonymy: Comandraceae Nickrent & Der
[Thesieae + Cervantesieae]: ovules unitegmic.
2. Thesieae Meisner
?Santalbic acid; (K +, [strongly lobed]); (C connate); nectary glands?; ovules unitegmic; n = 6-9(-12).
5/345: Thesium (345). More or less world-wide, not Arctic; Thesium esp. Africa.
Synonymy: Thesiaceae Vest
3. Cervantesia group
(Plant with axillary thorns); (lamina rhombic, with spines - Jodina); n = ?
8/21. Tropical, warm temperate, esp. America.
Synonymy: Cervantesiaceae Nickrent & Der
[Nanodea group [Santaleae [Amphorogyneae + Visceae]]]: ?
4. Nanodea group
?Santalbic acid; (flowers 4 merous); (K +); (G semi-inferior); n = ?
2/2. South Temperate.
Synonymy: Nanodeaceae Nickrent & Der
[Santaleae [Amphorogyneae + Visceae]]: (stem parasites +); (cuticular epithelium +); (ovules reduced to embryo sac).
Age. The age of this node is some (71-)67, 65(-61) or (57-)53(-49) m.y. (Wikström et al. 2001).
5. Santaleae Dumortier
(Stem parasites); cuticular epithelium +; (leaves spiral); (K +); (large nectaries alternating with A - Osyris); (G half inferior); embryo sac with micropylar end long-protruding, (embryo sac bisporic, 8-nucleate [Allium type]); (seed with a complete viscous covering); (chalazal endosperm haustorium multicellular - Exocarpus), (endosperm green); n = 10, 11, 13, 15.
11/51: Exocarpus (26). Widely scattered, not N. temperate.
Synonymy: Canopodaceae C. Presl, Eremolepidaceae Nakai, Exocarpaceae J. Agardh, Lepidocerataceae Nakai, Osyridaceae Rafinesque
[Amphorogyneae + Visceae]: stamens with short filaments.
Age. Stem Visceae, i.e. the age of this node, are some 72 m.y. old (Vidal-Russell & Nickrent 2008).
6. Amphorogyneae Stearn
(Stem parasites); pyrrolizine alkaloids +; flowers 4-6-merous, (C connate); anthers with loculi above one another in pairs, loculi opening separately; n = ?
9/68: Dendromyza (21), Leptomeria (17). Southeast Asia, Malesia, Australia and New Caledonia.
Synonymy: Amphorogynaceae Nickrent & Der
7. Visceae Horaninow
Stem parasites, often with haustoria ramifying through the host, no roots running over the surface°; methylated cyclitols, myricetin, caffeic acid esters, toxic polypeptides +; cuticular epithelium +; stems brittle and jointed°, stomata transverse; cuticle waxes usu. platelets with irregular margins; leaves opposite, lamina with secondary veins usu. ± palmate, petiole obscure; plant monoecious° (dioecious - Viscum), (flowers sometimes perfect - Phacellaria); no bract and bracteole immediately under the ovary°; flower 3-4(-5)-merous°, short° [<4 mm long]; anthers opening by pores°, (longitudinally), (polythecate), (connate, forming a synandrium, opening circumferentially); pollen spherical°; G with style short, mamelon + (0), 2 "ovules"°; embryo sac bisporic, 8-nucleate [Allium type], (monosporic, 8-nucleate [Polygonum type] - Viscum minimum), (elongated), (straight), (micropylar [egg cel] end outside mamelon - Phoradendron, etc.); "berry" sometimes explosive, viscous covering +, incomplete, inside the vascular bundles°, consisting of polysaccharide threads and mucilage°, thin endocarp +° (always?); endosperm green°, starchy, (plane of first cleavage of zygote vertical - Korthalsella, Arceuthobium), suspensor short or 0, embryo green, with 1 cotyledon [= 2 connate]; n = 10-14(-17).
7/520: Phoradendron (235), Viscum (65-150), Dendrophthora (70). Worldwide (Map: from Barlow 1983; Fl. Austral. 22. 1984; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010 - note that Barlow has the group through much of the northern Sudano-Sahelian-Zambezian zone...).
Synonymy: Arceuthobiaceae Nakai, Dendrophthoraceae van Tieghem, Ginalloaceae van Tieghem, Phoradendraceae H. Karsten, Viscaceae Batsch
Evolution. Divergence & Distribution. Visceae have perhaps been branch parasites for much of the 72 m.y. the clade may have existed (Vidal-Russell & Nickrent 2008). The large genus Thesium may be of South African origin, with a stem age of ca 60 m.y. and a crown age of (56.5-)42.7-35.9(-24.4) m.y. (Moore et al. 2010: a variety of analyses). Santalum, the sandalwood genus, is centred on Australia and the Pacific, and there have perhaps been two migrations from Australia to Hawaii and also two migrations out of Hawaii to the south Pacific (Harbaugh & Baldwin 2007).
The leaves of Viscum crassulae are supposed to mimic those of its preferred host, Portulacaria afra (Didieraceae: ?reference).
Ecology & Physiology. For root parasitism in Santalum album, see Tennakoon and Cameron (2006). The branch-parasitic habit seems to have evolved three times in Santalaceae, in the Viscum, Eremolepis and Dendromyza groups (Der & Nickrent 2008; Vidal-Russell & Nickrent 2008); the latter two are in Santaleae and Amphorogyneae respectively. Expanded wood roses may be produced by the host at places where the parasite attaches. Press and Phoenix (2005) discussed host-parasite interactions of Visceae (see also below). Phacellaria (Visceae) is an obligate hyperparasite on a few other Santalaceae (Dendrophthoë) and especially Loranthaceae, Taxillus in particular (Li & Ding 2006; see also Mathiasen et al. 2008), while Phoradendron durangense and P. falcatum parasitize only other species of Phoradendron (Calvin & Wilson 2009). Most species of the dwarf mistletoe Arceuthobium parasitize Pinaceae, with a few species also groing on Juniperus, in Cupressaceae (Farjon 2008). Some species of Arceuthobium and Viscum are almost holoparasites, being largely endophytic (Nickrent & García 2009; Mauseth & Rezaei 2013).
The mistletoe Viscum minimum, from the eastern Cape, has aerial stems about 3 mm long and with but a single internode (Don Kirkup, pers. comm.); these arise from the endophytic portion of the plant (for its growth, see Mauseth & Rezaei 2013). It is also an indicator of elephant grazing; the animals preferentially eat branches on which it is growing since it is succulent and nutrient-rich (Germishuizen et al. 2007, and references: see also Loranthaceae).
Pollination Biology & Seed Dispersal. In Santalum, filament hairs are involved in secondary pollen presentation (Howell et al. 1993), while some Visceae are wind pollinated.
Many mistletoes and their relatives and other stem parasitic Santalaceae have fleshy fruits and are dispersed by birds in a fashion rather similar to the fleshy fruits of Loranthaceae; again, strings of seeds, "rosaries", from the bird faeces may dangle from the branch (Godschalk 1983; Restrepo 1987: South American species; Watson 2001). In Arceuthobium seed discharge is explosive, the seed leaving the fruit at about 1370 cm/second and travelling up to 20 meters (66 feet) (Hinds et al. 1963; Hawksworth & Wiens 1996). Fertilization may be considerably delayed after pollination (Ross & Sumner 2005); the seeds can take two years to mature and the embryo lacks a plumule but has a well developed radicle (Ross Friedman & Sumner 2009).
Genes & Genomes. Molecular evolution has greatly speeded up in the Viscum clade (Vidal-Russell & Nickrent 2008). A very large genome with a C value of some 350 picograms or more is found in Viscum alone of the Santalales examined (Leich et al. 2005).
Economic Importance. Mathiasen et al. (2008) provide a list of Santalaceae that harm crops and timber trees. Species of Arceuthobium (e.g. A. americanum) in particular are major pests on conifers in west North America in particular, causing extensive witches' brooms and the ultimate death of the host.
Chemistry, Morphology, etc. Subepidermal cells of the stem divide irregularly, the outer walls being cutinised; this is the cuticular epithelium, and it lacks both suberin (c.f. cork) and lenticels, and there is no cork cambium (Wilson & Calvin 2003). It is present in Eremolepidaceae (Santaleae) and Visceae, as well as in other Santalaceae; its distrbution needs clarification. Stomata on the stem and leaf are commonly tranversely oriented (Butterfass 1987).
A number of Santalaceae have three traces in their perianth members, the two lateral traces coming from commissural bundles (Smith & Smith 1943).
Some Santalaceae have recurrent bundles in the gynoecium, perhaps evidence of receptacular epigyny (Eyde 1975, and references); however, Exocarpus and some other genera have a superior ovary. For information on genes expressed during ovule/embryo sac development, see Brown et al. (2010); in taxa with higly reduced ovules genes normally expressed in integuments are expressed in the tissues immediately surrounding the embryo sac and in the wall surrounding the loculus. Ross and Sumner (2005: Arceuthobium) describe the antipodal end of the embryo sac as being apical on the mamelon, while Zaki and Kuijt (1994: Viscum) show it as being apical; there seems to be variation here (see also Rutishauser 1935). Thesium has starchy endosperm. Antidaphne seems to have three vascular traces in its cotyledons.
See Wiens and Barlow (1971) for cytology, Benzing (1990) for growth, etc., of stem parasitic members of the family, Norverto (2004, 2011) for wood anatomy, Wilson and Calvin (2003) for some aspects of anatomy, Steindl (1935), Bhandari and Vohra (1983) and Zaki and Kuijt (1995) and references for embryology, about which there is quite a bit of information, especially for Viscoideae, Leins (2000) for floral morphology of Viscum and Ronse de Craene and Brockington (2013) for flowers of Colpoon.
Phylogeny. Der and Nickrent (2005, esp. 2008; see also Nickrent et al. 1998) found seven well supported clades in Santalaceae (see the groups above), but relationships between these clades are poorly understood; there may be a clade including most of the family except the Cervantesia, Thesium and Comandra clades. There is very slight support for a [Cervantesieae + Thesieae] clade, and some support for a [Amphorogyneae + Visceae] clade, etc.
Genera of Eremolepidaceae, very often kept separate before, that were studied by Der and Nickrent (2008: Eremolepis not included) are well embedded in the Santalum clade (Der & Nickrent 2008), their strongly supported relationships being [Antidapne [Lepidoceras + Eubrachion]]. See Nickrent et al. (2004b: ?rooting) for a relationships in Arceuthobium, Nickrent et al. (2008) and Moore et al. (2010) for those within the large genus Thesium, and Harbaugh and Baldwin (2007) for the phylogeny of Santalum, the sandalwood genus.
Two groups, both stem parasites, are morphologically rather distinctive:
Classification. Der and Nickrent (2005) proposed that all major clades in Santalaceae should be recognized as families; the seven families listed there are the necessary result if Viscaceae are to be kept separate (see also Nickrent et al. 2010); apart from Visceae and Amphorogyneae, distinctive features for the clades are elusive. For a monograph of Phoradendron, see Kuijt (2003), for the circumscription of Thesium, see Moore et al. (2010).
Botanical Trivia. Viscum crassulae is a pleasing horticultural subject with its bright red fruits; it must be about the only stem parasite so grown.
BALANOPHORACEAE Richard, nom. cons. Back to Santalales
Root parasites, echlorophyllous, with underground tuber-like structures either parasite or parasite-host mixed, these rupture and leave a collar-like structure at ground level; shoot endogenous, apex develops inside schizogenous cavity [Balanophora]; santalbic acid?, plant tanniniferous; roots 0; cork ?; vessel elements with simple perforation plates; cuticle wax crystalloids 0; stems endogenous; leaves spiral, two-ranked, whorled or 0; plant monoecious or dioecious; inflorescence racemose, ± capitate or spicate, terminal; flowers small, (monosymmetric); staminate flowers: P 0, 3-4(-8), valvate (imbricate), (basally connate); stamens equal and opposite perianth members, (1-2, esp when P = 0), extrorse, usu. connate, (thecae connate), (endothecium biseriate); tapetal cells uninucleate [Lophophytum]; pollen grains (tricellular), (syn)tricolpate or tri- or pantoporate; pistillode 0 (+); carpellate flowers: P 0 or minute; staminodes 0; G [2, 3(-5)], (inferior), [2 transverse - Rhophalocnemis], or acarpellate, styluli + or style single, stigma punctate or ± expanded; "ovules" 1/carpel, ategmic, reduced to an embryo sac; embryo sac usu. bisporic [chalazal spores], 8-celled [Allium type], (chalazal caecum 0), (antipodal cells 0); fruits minute, drupes or nut-like; endosperm persistent, chalazal haustorium single-celled, plane of first cleavage of zygote vertical, embryo short to undifferentiated, suspensor 0; n = 14, ?16, 18; germination via germ tube.
17[list]/50: Balanophora (15). Mostly tropical (map: from Hansen 1972, 1980, 1986; van Balgooy 1975; Heide-Jørgensen 2008; Trop. Afr. Fl. Pl. Ecol. Distr. 5. 2010). [Photo - Flower]
Age. Naumann et al. (2013) estimated the age of a clade [Balanophoraceae [Loranthaceae + Schopfiaceae]], the only Santalales in the study, at (119.5-)109.7(-98.7) m.y., but if Balanophoraceae are not immediately related to the [Loranthaceae + Schopfiaceae] clade, its age becomes uncertain.
Evolution. Ecology & Physiology. How the host is infected varies. Balanophora abbreviata attaches to the host by sticky endosperm tubules, tubular embryonal primary haustorium processes then infecting the host (Arekal & Shivamurthy 1976); the process looks like infection by a T4 phage. Holzapfel (2001) recorded a radicle in Dactylanthus taylori that attached to the host by epidermal hairs.
Genes & Genomes. The mitochondral genes cox1, atp1 and matR showed massive divergence (Barkman et al. 2007: Ombrophytum only sampled).
Chemistry, Morphology, etc. Langsdorffia, Thonningia and Balanophora have balanophorin, a wax-like substance, rather than starch as the main reserve. Weber (1986) noted several distinctive aspects of gross morphology and detailed anatomy of the haustoria of Mystropetalon such as runners that produced additional haustoria and graniferous tracheary cells in these haustoria that were similar to comparable structures in Santalales, however, graniferous cells occur in other root parasites including Krameriaceae and Orobanchaceae (Fineran & Ingerfeld 1982). For the development of the short, see Shivamurthy et al. (1981), and for anatomy of the vegetative body, see Gonzalez and Mauseth (2010).
It can be very difficult to understand the morphology of the flower, the number of stamens, whether the ovary is superior or inferior, etc., although there are a fair number of detailed early studies on individual species of the family. The florally relatively unspecialized Mystropetalon has a clearly inferior ovary and cuboid pollen with pores at the eight corners; variously angled pollen is known from other Santalales.
Eberwein et al. (2009) note that the carpellate flowers of Balanophora may entirely lack any appendages and be adnate to clavate bodies, perhaps modified bracts, that are borne in no particular order in the inflorecence. Given the extreme reduction of the flower, the basic morphology of the ovule, fruit, etc., become unclear. For cautionary comments on attempts to determine ovule type and orientation in the family, see Holzappel (2001). Thus Fagerlind (e.g. 1945c) notes that the "apical" cell of the megaspore tetrad in Langsdorffia develops into the embryo sac, but determination of what is apex and base is impossible. Embryo sac development varies, and in Balanophora and Langsdorffia, at least, there is a chalazal caecum, as in many other Santalales, but such a caecum is weakly developed in Dactylanthus and absent in Corynaea (Johri et al. 1992; Holzapfel 2001). Holzapfel (2001) noted a pseudoendothelium was quite common in the family. Dactylanthus lacks any seed coat. Endosperm development is sometimes categorized as "helobial". The basal cell produced by the first division of the endosperm nucleus is massive and the nucleus usually remains undivided (if it does, cell walls do not form - Ernst 1914); it is perhaps to be compared with the chalazal haustorium in other Santalales. Dahlgren (1923) called the endosperm cellular. Division of the smaller upper cell and its descendants always involves the formation of cell walls (see also Ekambaram & Panje 1935). In Helosis the inner layer of cells of the seed coat is massively thickened on the inner and anticlinal walls, while in Balanophora it is the outer layer that is thickened; taxa like Hachettia are more complex.
Takhtajan (1988, 1997) provides much information under the segregate families mentioned below, including Hachettiaceae and Lathraeophyllaceae (= Helosidaceae); see also Harms (1935b), Fagerlind (1938a, 1945b, c, d) and Sato and Gonzalez (2013), all embryogeny, and Kuijt (1969), the Parasitic Plants website (Nickrent 1998 onwards) and Heide-Jørgensen (2008), all general.
Phylogeny. A family phylogeny (Nickrent 1998: accessed 16.5.2009) based on nuclear SSU rDNA data suggest that [Mystropetalon [Dactylanthus + Hachettea]] are sister to a clade containing the rest of the family examined; see also Su et al. (2012: unrooted tree).
Previous Relationships. Cronquist (1968) thought that Balanophoraceae (including Cynomoriaceae, here Saxifragales) and Santalales were related, and later (Cronquist 1981) he placed them all in Santalales. Takhtajan (1997) linked Balanophoraceae with Cynomoriaceae, Rafflesiales (here Malpighiales) and Hydnoraceae (here Piperales), including them all in his Magnoliidae; within Balanophorales he included all the families in synonymy below (apart from Hachetteaceae) as separate families.
Botanical Trivia. Balanophora has the smallest flowers of any angiosperm; they may have a mere 50 cells in total.
Synonymy: Dactylanthaceae Takhtajan, Hachetteaceae Doweld, Helosidaceae Bromhead, Langsdorffiaceae Pilger, Lophophytaceae Bromhead, Mystropetalaceae J. D. Hooker, Sarcophytaceae A. Kerner, Scybaliaceae A. Kerner