Habit and leaf form. Large, tough herbs. ‘Normal’ plants, or switch-plants (? — cf. the peculiar leaf blade vascularization). With a basal aggregation of leaves; rhizomatous. Leaves alternate; four-ranked, or tristichous; flat (or canaliculate); leathery; sessile; sheathing; simple. Lamina entire; linear; parallel-veined. Lamina margins minutely serrate, or entire. Leaves presumably with a persistent basal meristem, and basipetal development.
General anatomy. Plants with silica bodies (spheroidal, in the epidermis and parenchyma).
Leaf anatomy. Epidermis containing silica bodies. Stomata present; paracytic, or tetracytic.
Lamina with the vascular bundles arranged in vertical pairs, with the phloem orientated to the inside — i.e., the upper bundles ‘normal’, the lower ‘inverted’. The mesophyll not containing mucilage cells; (calcium oxalate) without calcium oxalate crystals. Vessels present; end-walls scalariform.
Stem anatomy. Young stems bluntly tetragonal, or triangular in section. Secondary thickening absent. Xylem with vessels. Vessel end-walls oblique; scalariform, or scalariform and simple (mainly scalariform).
Root anatomy. Root xylem with vessels (perforation plates scalariform).
Reproductive type, pollination. Plants hermaphrodite. Floral nectaries absent (no nectaries). Pollination anemophilous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in heads (densely concentrated). The ultimate inflorescence unit (the head) racemose. Inflorescences of one or several heads; with involucral bracts; pseudanthial. Flowers small (with short, swollen, puberulous pedicels); regular; 3 merous; cyclic. Perigone tube absent. Hypogynous disk absent.
Perianth of ‘tepals’; 6; free; 2 whorled (3+3); isomerous; sepaloid, or petaloid (the members thin, narrow, hyaline, persistent, obtuse); similar in the two whorls (chaffy); hyaline; persistent.
Androecium 6. Androecial members free of the perianth to adnate (the filaments somewhat adnate to the tepals at their bases); free of one another; 2 whorled (3+3). Androecium exclusively of fertile stamens. Stamens 6; diplostemonous; filantherous (the filaments thin and relatively long). Anthers basifixed; dehiscing via longitudinal slits; tetrasporangiate. Pollen shed in aggregates; in tetrads (tetrahedral). Pollen grains aperturate; 1 aperturate; ulcerate (cf. Juncaceae).
Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 3 celled. Gynoecium syncarpous; synovarious to synstylovarious (short styled, with three long stigmatic branches); superior. Ovary 3 locular. Gynoecium shortly stylate. Styles 1; attenuate from the ovary; apical. Stigmas 3. Placentation basal, or axile. Ovules 1–7 per locule (to ‘several’); ascending; apotropous; anatropous.
Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit 3 seeded (triangular). Seeds endospermic (the nucellus and enclosed endosperm free from the seed coat, except at the micropylar end); conspicuously hairy (hispid); winged (with a hispid, subulate process at each end). Embryo well differentiated (small). Cotyledons 1. Embryo straight (cylindrical). Testa without phytomelan; brown (thick).
Physiology, biochemistry. Not cyanogenic.
Geography, cytology. Neotropical. Tropical. Northeast Brazil, Guiana.
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Commeliniflorae; Cyperales. APG 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Poales.
Species 3. Genera 1; only genus, Thurnia.