Trapellaceae (F.W. Oliver) Honda & Sakisake
Habit and leaf form. Aquatic herbs. Perennial; rhizomatous. Hydrophytic; rooted (with creeping rhizome and floating stems). Leaves submerged and floating. Heterophyllous (the lower leaves narrow, oblong, remotely serrate, the floating leaves broad, deltoid-rotundate, crenate). Leaves opposite; simple. Lamina entire. Leaves exstipulate. Lamina margins crenate (floating), or serrate (submerged).
Leaf anatomy. Hydathodes present (in the indentations of the blade margins). Stomata when present, anomocytic.
Stem anatomy. Vessel end-walls simple.
Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary (chasmogamous floating and cleistogamous submerged); axillary (usually only one developed at each node despite the opposite leaves); very irregular; zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers cyclic; tetracyclic. Free hypanthium absent.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; persistent; imbricate; with the median member posterior. Corolla 5; 1 whorled; gamopetalous; imbricate; slightly bilabiate (with two upper and three lower lobes, the upper lip exterior).
Androecium 4. Androecial members adnate (to the corolla); free of one another; 1 whorled. Androecium including staminodes. Staminodes 2; in the same series as the fertile stamens; representing the anterior-lateral pair (anticolous). Fertile stamens representing the posterior-lateral pair (latero-posterior). Stamens 2; reduced in number relative to the adjacent perianth; oppositisepalous; alternating with the corolla members; filantherous (the filaments filiform). Anthers borne on a large, peltate connective, included. Pollen grains aperturate; 3 aperturate; colporate (colporoidate, the oroids provided with operculoid membranes).
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior. Ovary 2 locular. Locules without ‘false septa’. Gynoecium median; stylate. Styles 1; apical. Stigmas unequally 2 lobed. Placentation axile to apical. Ovules 2 per locule (in the posterior locule only, the anterior abortive and empty); pendulous; anatropous; unitegmic; tenuinucellate. Endosperm formation cellular.
Fruit non-fleshy; indehiscent; a nut (conspicuously appendaged). Dispersal unit crowned with five spreading, rigid appendages below the calyx, three elongate, slender and uncinate, the other two short, subulate and spinose. Fruit 1 seeded. Seeds thinly endospermic. Embryo straight.
Geography, cytology. Holarctic. Temperate to tropical. Eastern Asia.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Scrophulariales. Cronquist’s Subclass Asteridae; Scrophulariales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales (as a synonym of Pedaliaceae).
Species 2. Genera 1; only genus, Trapella.