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The families of flowering plants

L. Watson and M.J. Dallwitz

Trapellaceae (F.W. Oliver) Honda & Sakisake

~ Pedaliaceae.

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 leaves), or serrate (submerged leaves).

Leaf anatomy. Hydathodes present (in the indentations of the blade margins). Stomata present (but absent from submerged leaves); mainly confined to one surface (i.e., on the upper surfaces of floating leaves); anomocytic.

Axial (stem, wood) anatomy. The 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 included, borne on a large, peltate connective. 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 one 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.

General remarks. Differing conspicuously from Pedaliaceae (q.v.) in habitat, polysepaly, A4 comprising 2 fertile stamens and 2 anterior-lateral staminodes, and the inferior ovary; also in the records of colporate pollen and amyloid-negative seeds.

Illustrations. • Trapella sinensis: Nat. Pflanzenfam. IV (1895). • Trapella sinensis: Hook. Ic. Pl. 16 (1887).


We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.


Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 20th July 2017. delta-intkey.com/angio’.

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