Thunbergiaceae Van Tiegh.
~ Acanthaceae p.p.
Including Meyeniaceae Sreemadhavan
Habit and leaf form. Shrubs, or lianas, or herbs. Self supporting, or climbing; the climbers stem twiners (the stems commonly articulated); Thunbergia twining anticlockwise. Mesophytic. Leaves opposite; petiolate; simple. Lamina entire; pinnately veined, or palmately veined (?); cross-venulate; hastate, or attenuate at the base, or rounded at the base. Leaves exstipulate; without a persistent basal meristem.
Leaf anatomy. Minor leaf veins with phloem transfer cells, or without phloem transfer cells (variably present, in Thunbergia).
Stem anatomy. Cork cambium present; initially superficial. Internal phloem present, or absent (?). Secondary thickening developing from a conventional cambial ring, or anomalous (Thunbergia); from a single cambial ring. ‘Included’ phloem present (Thunbergia), or absent (?).
Reproductive type, pollination. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, axillary; when aggregated, in racemes. The terminal inflorescence unit racemose. Inflorescences terminal; racemes. Flowers bracteate; (bi-) bracteolate (the bracteoles large, spathaceous, by contast with the reduced calyx); regular, or somewhat irregular; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present (large); intrastaminal; annular (more strongly developed adaxially).
Perianth with distinct calyx and corolla, or petaline (the calyx always reduced, sometimes obsolete, its functions assumed by the large bracteoles); 10–21; 1 whorled, or 2 whorled; isomerous, or anisomerous. Calyx when ascertainable, 5–16 (sometimes ringlike); 1 whorled; gamosepalous; entire, or lobulate, or blunt-lobed, or toothed; unequal but not bilabiate, or regular. Corolla 5; 1 whorled; gamopetalous; contorted (left-contorted in Thunbergia); hypocrateriform; unequal but not bilabiate, or regular.
Androecium 4, or 5. Androecial members adnate (to the corolla); markedly unequal; free of one another; 1 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 1 (minute); in the same series as the fertile stamens; representing the posterior median member; non-petaloid (the posterior androecial member reduced or missing). Fertile stamens representing the posterior-lateral pair and the anterior-lateral pair, or the posterior median member, the posterior-lateral pair, and the anterior-lateral pair. Stamens 4; inserted near the base of the corolla tube; didynamous; reduced in number relative to the adjacent perianth; oppositisepalous; alternating with the corolla members. Anthers dorsifixed; dehiscing via longitudinal slits; tetrasporangiate; appendaged, or unappendaged. The anther appendages when present, basal (in the form of awns or bristles). Anther epidermis persistent. Microsporogenesis simultaneous. Anther wall initially with more than one middle layer (2 to 3); of the ‘dicot’ type. Pollen grains aperturate; spiraperturate.
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 2 locular. Gynoecium median; stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; large, funnel-shaped or bilobed; wet type; papillate; Group III type. Placentation axile. Ovules 2 per locule; collateral; hemianatropous, or anatropous, or campylotropous; unitegmic; tenuinucellate. Endothelium not differentiated. Endosperm formation cellular.
Fruit non-fleshy; dehiscent; a capsule (with a large ensiform beak). Capsules loculicidal. Seeds non-endospermic; with amyloid. Embryo well differentiated. Embryo curved.
Physiology, biochemistry. Not cyanogenic. Iridoids detected (in Thunbergia); ‘Route II’ type (+decarb., including stilbericoside). Proanthocyanidins absent. Ellagic acid absent (Thunbergia). Saponins/sapogenins absent. C3. Anatomy non-C4 type (Thunbergia).
Peculiar feature. The funicles not as in Acanthaceae (retinacula absent or much reduced).
Geography, cytology. Paleotropical, Neotropical, Cape, and Australian. Tropical. Pantropical.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Scrophulariales. Cronquist’s Subclass Asteridae; Scrophulariales. APG (1998) Eudicot; core Eudicot; Asterid; Euasterid I; Lamiales (as a synonym of Acanthaceae). Species 205. Genera 4; Thunbergia, Pseudocalyx, Meyenia, Whitfieldia (Pounguia).
Illustrations. • Thunbergia spp..
Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).
