EXTANT SEED PLANTS

Plant woody, evergreen; nicotinic acid metabolised to trigonelline; primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins rich in guaiacyl units; true roots present, xylem exarch, branching endogenous; arbuscular mycorrhizae +; shoot apical meristem complex; 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(-8) mm/mm²; plant heterosporous, sporangia eusporangiate, on sporophylls, sporophylls aggregated in indeterminate cones/strobili; true pollen [microspores] +, 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, 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 via tyrosine pathway [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 sieve plate, companion cells from same mother cell that gave rise to the tube, the sieve tube with P-proteins; nodes unilacunar; stomata with ends of guard cells level with aperture, paracytic; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, vein endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, development in general centripetal, numbers unstable, P not 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, exine columellar, endexine thin, compact, lamellate only in the apertural regions, 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, 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 ?type, stylulus short, hollow, stigma ± decurrent, wet [secretory]; P deciduous in fruit; seed exotestal; 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; 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/PHYC gene pairs.

Possible apomorphies 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. Furthermore, details of relationships among gymnosperms will affect the level at which some of these characters are pegged.

NYMPHAEALES + AUSTROBAILEYALES + (MONOCOTS + CERATOPHYLLALES) + (CHLORANTHALES + MAGNOLIIDS + EUDICOTS): pollen tectate-columellate, tectum reticulate [perforated]; nucleus of egg cell sister to one of the polar nuclei; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

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

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).

The relationships between commelinids, Asparagales, Dioscoreales, Liliales, and Pandanales have been somewhat unclear. 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 may be separate from other Asparagales (the latter being sister to commelinids) and that Dioscoreales and Pandanales form a clade. However, a recent two-gene (matK, rbcL) study (Tamura et al. 2004) seems to clarify the situation considerably. Petrosaviaceae (both genera were studied) are sister to Dioscoreaceae + Pandanaceae plus all other groups, then Liliales diverge, while Asparagales are sister to the commelinids (i.e. a topology rather like the first resolved tree mentioned above in Chase et al. 2000a). Support is quite high (³85% bootstrap) for all order and family branches, although rather lower for Asparagales + commelinids (68%). The topology in Janssen and Bremer (2004) is broadly similar, except that the orders just mentioned represent 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. 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 summarise earlier literature on relationships of the two).

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 seems 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).

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).

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

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

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).

Synonymy: Japonoliriaceae Takhtajan, Miyoshiaceae Nakai