EXTANT SEED PLANTS

Plant woody, 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 rich in guaiacyl units; true roots present, apex multicellular, xylem exarch, branching endogenous; arbuscular mycorrhizae +; shoot apical meristem multicellular, interface specific plasmodesmatal network; stem with ectophloic eustele, endodermis 0, xylem endarch, branching exogenous; vascular tissue in t.s. discontinuous by interfascicular regions; vascular cambium + [xylem ("wood") differentiating internally, phloem externally]; wood homoxylous, tracheids +; tracheid/tracheid pits circular, bordered; sieve tube/cell plastids with starch grains; phloem fibers +; stem cork cambium superficial, root cork cambium deep seated; nodes ?; stomata ?; leaf vascular bundles collateral; leaves spiral, simple, axillary buds?, prophylls [including bracteoles] two, lateral, veins -5 mm/mm² [mean for all non-angiosperms 1.8]; plant heterosporous, sporangia eusporangiate, on sporophylls, sporophylls aggregated in indeterminate cones/strobili; true pollen [microspores, i.e. no distal pore for release of gametes] +, grains mono[ana]sulcate, exine and intine homogeneous, ovules unitegmic, crassinucellate, megaspore tetrad tetrahedral, only one megaspore develops, megasporangium indehiscent; male gametophyte development first endo- then exosporic, tube developing from distal end of grain, to ca 2 mm from receptive surface to egg, gametes two, with cell walls, with many flagellae; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large", first cell wall of zygote transverse, embryo straight, endoscopic [suspensor +], short-minute, with morphological dormancy, white, cotyledons 2; plastid transmission maternal; two copies of LEAFY gene, PHY gene duplication [N/O//A/C and P//BE lines], mitochondrial nad1 intron 2 and coxIIi3 intron present.

MAGNOLIOPHYTA

Plant woody, evergreen; lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], lignins derived from both coniferyl and sinapyl alcohols, containing syringaldehyde [in positive Maüle reaction, syringyl:guaiacyl ratio less 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; stem with 2-layered tunica-corpus construction; wood fibers and wood parenchyma +; reaction wood ?, with gelatinous fibres; starch grains simple; primary cell wall mostly with pectic polysaccharides; tracheids +; sieve tubes eunucleate, with a sieve plate and cytoplasm with P-proteins, companion cells from same mother cell that gave rise to the sieve tube; nodes unilacunar [1:?]; stomata with ends of guard cells level with pore, paracytic, outer stomatal ledges producing vestibule; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, veins (1.7-)4.1(-5.7) mm/mm², endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, development in general centripetal, numbers unstable; P not sharply differentiated, outer members not enclosing the rest of the bud, smaller than inner members; A many, with a single trace, introrse, filaments stout, anther ± embedded in the filament, tetrasporangiate, dithecal, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally by action of hypodermal endothecium, endothecial cells elongated at right angles to long axis of anther; tapetum glandular, binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, binucleate at dispersal, trinucleate eventually, tectum continuous or microperforate, ektexine columellar, endexine thin, compact, lamellate only in the apertural regions; nectary 0; G free, several, ascidiate, with postgenital occlusion by secretion, few [?1] ovules/carpel, ovules marginal, anatropous, bitegmic, [outer integument often largely subdermal in origin, inner integument dermal], micropyle endostomal, integuments 2-3 cells thick, megasporocyte single, megaspore lacking sporopollenin and cuticle, chalazal, female gametophyte four-celled [one-modular, nucleus of egg cell sister to one of the polar nuclei], stylulus short, hollow, stigma ± decurrent, dry [not secretory]; P deciduous in fruit; seed exotestal; pollen germinating in less than 3 hours, tube elongated, growing at 80-600 µm/hour, with callose plugs and callose-based walls, penetrating between cells, siphonogamy, penetration of ovules within ca 18 hours, distance to first ovule 1.1.-2.1 mm; double fertilisation +, endosperm diploid, cellular [first division oblique, micropylar end initially with a single large cell, chalazal end more actively dividing], copious, oily and/or proteinaceous, embryo cellular ab initio, minute; germination hypogeal, seedlings/young plants sympodial; Arabidopsis-type telomeres [(TTTAGGG)_n]; whole genome duplication, 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 PHYA + C/PHYB + E gene pairs.

Evolution. Possible apomorphies for flowering plants are in bold. Note that the actual level to which many of these features, particularly the more cryptic ones, should be assigned is unclear, because some taxa basal to the [magnoliid + monocot + eudicot] group have been surprisingly little studied, there is considerable variation between families in particular for several of these characters, and also because details of relationships among gymnosperms will affect the level at which some of these characters are pegged. For example, if reticulate-perforate pollen is optimized to the next node on the tree (see Friis et al. 2009 for a discussion), it effectively makes the pollen morphology of the common ancestor of all angiosperms ambiguous....

NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessels +, elements with scalariform perforation plates, axial parenchyma diffuse or diffuse-in-aggregate; tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]: cyanogenic glycosides uncommon; starch grains simple, amylophobic; stomata anomocytic, (cuticular waxes as parallel platelets); colleters 0; endosperm nuclear.

Evolution. The stem-group age of this whole group ("core monocots") is ca 131 million years before present, the crown group age ca 126 million years before present. Subsequent branching in this general part of the tree - i.e. the Petrosaviales, Dioscoreales + Pandanales, and Liliales clades, and including crown group Petrosaviales, may be somewhere around 125-120 million years before present (ca 111 million years before present in Bremer 2000b), and the stem groups of all other orders, including those in the commelinid group, diverge by ca 115 million years before present or soon afterwards (Janssen & Bremer 2004). These and also many clades within all these orders may have originated in Southern Gondwana, i.e. Antarctica, Australasia, and southern South America (Bremer & Janssen 2006).

Phylogeny. The relationships between commelinids, Asparagales, Dioscoreales, Liliales, and Pandanales remained unclear for some time. A three-gene (rbcL, atpB, 18S RNA) study (Chase et al. 2000a) showed a polychotomy of Petrosaviaceae, Dioscoreales, Pandanales, Liliales, Asparagales and commelinids, although a single shortest tree showed a pectinate structure with the taxa in the sequence of the list above; another analysis with placeholders for taxa missing some sequences gave a similar structure, except that Pandanales and Liliales were sister taxa. (Note that a combined morphological plus molecular tree in the same volume [Stevenson et al. 2000] suggested a substantially different set of relationships; bootstraps were not given.) Fay et al. (2000a) also suggested a sister relationship between Asparagales and commelinids, although sampling outside Asparagales was sketchy since it was outside their immediate interest. Hilu et al. (2003: matK) i.a. suggested that Orchidaceae might be separate from other Asparagales (the latter being sister to commelinids) and that Dioscoreales and Pandanales formed a clade.

However, a two-gene (matK, rbcL) study (Tamura et al. 2004) began to clarify the situation considerably. Petrosaviaceae (both genera were studied) were sister to a clade including [Dioscoreaceae + Pandanaceae], then Liliales diverged, while Asparagales were sister to the commelinids (i.e. a topology rather like that in the most parsimonious tree mentioned above in Chase et al. 2000a). Support was quite high (³85% bootstrap) for all order and family branches, although rather lower for [Asparagales + commelinids] (68%). The topology in Janssen and Bremer (2004) was broadly similar, except that the all orders just mentioned were successive branches of the tree. Davis et al. (2004) also found Petrosaviales to be sister to the same monocots, but with moderate to weak (>72%) support. Graham et al. (2006) in a study analysing considerable amounts of data also recovered relationships similar to those suggested by Tamura et al. (2004), all sister taxon relationships in this area having 94% or more support, although that for [Liliales [commelinids + Asparagales]] was only 70% (see also Givnish et al. 2006b; Chase et al. 2006). Dioscoreales and Pandanales are sister taxa in several studies (e.g. Hilu et al. 2003; Tamura et al. 2004; see also Graham et al. 2006; Chase et al. 2006). In general they are adjacent along the spine in trees where the major polychotomy in the monocots (inc. Asparagales, Liliales) is resolved (e.g. Janssen & Bremer 2004; Bremer & Janssen 2006; Givnish et al. 2006b, not a strongly supported position), or are parts of adjacent branches (for the latter, see Davis et al. 2004, who also summarize earlier literature on relationships of the two).

Classification. Since no firm association of Petrosaviaceae with any other order has been supported, and its phylogenetic position, as in the tree here, seems well supported, a monofamilial Petrosaviales is appropriate.

PETROSAVIALES Takhtajan  Main Tree, Synapomorphies.

Stem with a ring of bundles; sieve tube plastids also with polygonal protein crystalloids; microsporogenesis simultaneous, pollen surface gemmate, styluli +, septal nectaries +; fruit a follicle.

The root stele is tri- or tetrarch.

Includes Petrosaviaceae. - 1 family, 2 genera, 4 species.

Synonymy: Miyoshiales Nakai - Petrosavianae Doweld

PETROSAVIACEAE Hutchinson

Rhizomatous, (echlorophyllous, mycoheterotrophic, vascular bundles forming a cylinder, vessels 0 - Petrosavia); hairs 0; leaves spiral, scaly on rhizome, base?; bracteoles sublateral or 0; T whorls slightly differentiated [outer somewhat smaller], members with a single trace, tube at most short; A inserted at base of T or free, ovary superior to semi-inferior, partly connate, plicate, fusion (congenital and) postgenital, 4-many ana-campylotropous ovules/carpel, integumentary obturator +, stigma subcapitate or decurrent; fruit also septicidal [Japonolirion], T persistent [?Petrosavia]; seeds obliquely arranged, winged or not, exotegmic [Japonolirion]; embryo small; n = 12, 13, 30; seedling?

2[list]/4. Japan and China, W. Malesia (map: from Jessop 1979).

Evolution. Stem-group Petrosaviaceae are dated to ca 126 million years before present, crown group Petrosaviaceae to ca 123 million years before present (Janssen & Bremer 2004).

Chemistry, Morphology, etc. The roots of Petrosavia have an unmedullated, four-radiate stele.

For general information, see Tamura (1998, in Nartheciaceae) and especially Cameron et al. (2003), for anatomy, see Stant (1970), for sieve tube plastids, see Behnke (2003), and for floral and inflorescence morphology, see Remizowa et al. (2006a, b) and Tobe (2008).

Previous Relationships. Petrosaviaceae have often been included in other families, thus Dahgren et al. (1985) placed them - along with representatives here placed in Nartheciaceae and Tofieldiaceae - in Melianthaceae, and while Tamura (1998) recognised a Petrosaviaceae, he also included members of Tofieldiaceae and Nartheciaceae in them. Petrosaviaceae s. str. (i.e. Petrosavia alone) were placed in Triuridales by Cronquist (1981) and in Triurididae by Takhtajan (1997); the latter included a monogeneric Japonoliriaceae in Melanthiales-Liliidae.

Synonymy: Japonoliriaceae Takhtajan, Miyoshiaceae Nakai