Alternatively Phylidreae (Phylidraceae) Lindl.
Habit and leaf form. Herbs. ‘Normal’ plants. Perennial; with a basal aggregation of leaves; rhizomatous, or cormous. Mesophytic, or xerophytic. Leaves alternate; spiral and distichous (the lower distichous, the upper spiral); flat; sessile; sheathing; edgewise to the stem (more or less, but sometimes subulate); simple. Lamina entire; linear, or lanceolate; parallel-veined; without cross-venules. Leaves eligulate; exstipulate. Lamina margins entire.
General anatomy. Accumulated starch other than exclusively ‘pteridophyte type’.
Leaf anatomy. Stomata present; paracytic.
Lamina isobilateral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals raphides. Minor leaf veins without phloem transfer cells (Orthothylax). Vessels absent.
Stem anatomy. Secondary thickening absent. Xylem without vessels.
Root anatomy. Root xylem with vessels; vessel end-walls scalariform.
Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present, or absent (? — no septal nectaries).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes. Inflorescences terminal; simple or compound spikes. Flowers bracteate (the bracts rather large, the flowers sometimes partially fused with them); small to medium-sized; fragrant, or odourless (sometimes?); very irregular; zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers cyclic; tetracyclic. Perigone tube absent.
Perianth of ‘tepals’; 6 (but diguisedly so); joined (the two lateral (upper) members of the inner whorl fused with the upper (median) of the outer whorl to form a large, broad upper lip, the median (lower) member of the inner whorl forming a large lower lip, and the laterals of the outer whorl small and sometimes fused with the solitary stamen); 2 whorled; theoretically isomerous; petaloid; white, or yellow.
Androecium 1. Androecial members free of the perianth, or adnate (sometimes adnate to the lateral tepals). Androecium exclusively of fertile stamens. Stamens 1; reduced in number relative to the adjacent perianth (i.e., reduced to the one stamen, which supposedly represents the median of an ancestral inner whorl). Filaments appendiculate (by virtue of adnation to one or both inner perianth members), or not appendiculate. Anthers versatile (peltate); dehiscing via longitudinal slits; extrorse to introrse (swinging over to become extrorse, or becoming helically coiled, at anthesis); tetrasporangiate. Endothecium developing fibrous thickenings. The endothecial thickenings spiral. Microsporogenesis successive. The initial microspore tetrads isobilateral. Anther wall initially with more than one middle layer (2 or 3). Tapetum glandular. Pollen shed in aggregates, or shed as single grains; in Philydrum, in tetrads. Pollen grains aperturate; 1 aperturate, or 3 aperturate; sulcate, or sulculate, or zoniaperturate; 2-celled.
Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 1 celled, or 3 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1 locular (in Philydrum, at least above the base), or 3 locular (septal nectaries absent). Gynoecium stylate. Styles 1; attenuate from the ovary, or from a depression at the top of the ovary; apical; shorter than the ovary to about as long as the ovary. Stigmas 1; 1 lobed, or 3 lobed; capitate; dry type; papillate; Group II type. Placentation in Philydrum (unilocular), parietal; usually axile. Ovules in the single cavity when unilocular 15–100 (‘many’); 15–50 per locule (‘many’); non-arillate; anatropous; bitegmic; crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation helobial.
Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal (usually), or splitting irregularly (rarely). Seeds copiously endospermic. Seeds with starch. Embryo well differentiated. Cotyledons 1. Embryo straight. Testa without phytomelan; brown.
Seedling. Hypocotyl internode absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.
Physiology, biochemistry. Not cyanogenic. Alkaloids absent (2 species). Proanthocyanidins present; cyanidin and delphinidin. Flavonols absent. Ellagic acid absent.
Geography, cytology. Sub-tropical to tropical. Southeast Asia, Malaysia, Australia. X = 8, 11.
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Bromeliiflorae; Philydrales. APG 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Commelinales.
Species 6. Genera 3, or 4; Helmholtzia, Philydrum, Orthothylax (= Helmholtzia), Philydrella.
• Technical details: Philydrella, Philydrum (Lindley).