Family Triuridaceae

Triuridaceae Gardn.

Habit and leaf form. Achlorophyllous, pallid or purplish herbs (lacking stomata, raphides and silica bodies, with fungal mycelium situated outside the plant and inside its subterranean parts). Leaves much reduced. Plants with roots; saprophytic (or more precisely, mycotrophic, since intracellular fungal tissues are digested by the plant). With neither basal nor terminal aggregations of leaves. Mesophytic. Leaves minute, or small; alternate; membranous; not imbricate; sessile; non-sheathing; simple. Lamina entire; one-veined; without cross-venules.

Leaf anatomy. Stomata absent.

The mesophyll without calcium oxalate crystals. Vessels absent.

Stem anatomy. Secondary thickening absent. Xylem without vessels.

Root anatomy. Root xylem without vessels (Andruris).

Reproductive type, pollination. Plants monoecious, or dioecious, or polygamomonoecious (?), or hermaphrodite (rarely — in some Sciaphila species). Pollination probably entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes (usually), or in cymes. The ultimate inflorescence unit racemose (usually), or cymose. Inflorescences terminal; sympodial in Triuris, otherwise racemes. Flowers bracteate; small; regular; not exhibiting the androecium internal to the gynoecium; cyclic; tetracyclic. Floral receptacle developing an androphore (Triuris), or developing a gynophore; not markedly hollowed. Perigone tube present (short, the lobes often reflexed).

Perianth of ‘tepals’; (3–)6(–10); joined; 1 whorled (valvate in bud); petaloid; without spots; white, or red to purple, or hyaline.

Androecium (2–)3(–6). Androecial members free of the perianth; all equal; free of one another, or coherent; 1 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes non-petaloid. Stamens (2–)3(–6); rather theoretically alterniperianthial (Sciaphileae), or oppositiperianthial (Triurideae); filantherous, or with sessile anthers (or, in Triuris, immersed in an androphore variously interpreted as representing receptacle or connective tissue). Anthers non-versatile; dehiscing via longitudinal slits, or dehiscing transversely (commonly), or dehiscing via longitudinal slits to dehiscing transversely (i.e., sometimes diagonally); extrorse; bilocular to four locular; tetrasporangiate (mostly), or bisporangiate (e.g. some Triuris), or bisporangiate to tetrasporangiate (often trisporangiate in Sciaphila); appendaged (by extension of the connective), or unappendaged. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis successive. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains nonaperturate; 3-celled (in Sciaphila).

Gynoecium 6–50 carpelled. Carpels isomerous with the perianth, or reduced in number relative to the perianth, or increased in number relative to the perianth. Gynoecium apocarpous; eu-apocarpous; superior. Carpel stylate; with a lateral style, or with a gynobasic style; 1 ovuled. Placentation basal. Stigmas papillate (Sciaphylla, Soridium), or non-papillate (the rest). Ovules funicled; ascending; non-arillate; anatropous; bitegmic; tenuinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type, or Fritillaria-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped. Endosperm formation nuclear.

Fruit non-fleshy; an aggregate. The fruiting carpel dehiscent (usually), or indehiscent (Soridium); a follicle, or an achene. Seeds copiously endospermic. Endosperm oily, or not oily (starch only in Triurideae). Embryo rudimentary at the time of seed release. Testa without phytomelan; thick.

Geography, cytology. Tropical. Pantropical and subtropical. X = 11, 12, 14.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Triuridiflorae; Triuridales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Pandanales.

Species 80. Genera 7; Andruris, Hexuris, Hyalisma, Sciaphila, Seychellaris, Soridium, Triuris.

Illustrations.
• Technical details: Hexuris, Sciaphila (Lindley).