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The families of flowering plants.                                                                                                                                                                

Thunbergiaceae Van Tiegh.

                        

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~Acanthaceae p.p.

IncludingMeyeniaceae 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 ultimate 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).

Perianthwith 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; 2-celled (Thunbergia).

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil2 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 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales (as a synonym of Acanthaceae).

Species 205. Genera 4; Thunbergia, Pseudocalyx, Meyenia, Whitfieldia (Pounguia).

 Illustrations:

  • Thunbergia species (Chittenden).
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