Nelsoniaceae
~ Acanthaceae
Habit and leaf form. Herbs. Leaves opposite; simple. Lamina entire. Leaves exstipulate.
Leaf anatomy. Cystoliths absent.
Stem anatomy. Internal phloem present. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; bracteate (the bracts leaflike); 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; gamosepalous; four blunt-lobed (the lower lobe bifid); contorted. Corolla 5; 1 whorled; gamopetalous; imbricate (descending cochlear); regular (the lobes equal — not bilabiate).
Androecium 2 (the posterior and the two anterior members missing). Androecial members adnate (to the corolla); free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 2; reduced in number relative to the adjacent perianth; oppositisepalous; alternating with the corolla members. Anthers dehiscing via longitudinal slits; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. Anther wall initially with one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3 aperturate; colporate (colporoidate); 2-celled.
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary 2 locular. Gynoecium median; stylate. Styles 1; apical. Stigmas 1, or 2. Placentation axile. Ovules 15–50 per locule (‘many’); unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Endosperm formation cellular. Embryogeny onagrad.
Fruit non-fleshy; dehiscent; a capsule. Seeds endospermic to non-endospermic. Endosperm ruminate; oily. Seeds small (and pitted). Embryo curved.
Physiology, biochemistry. Not cyanogenic. Iridoids detected (in Nelsonia); ‘Route II’ type (normal and decarb.).
Peculiar feature. The funicles not as in Acanthaceae (the retinacula absent or reduced to minute papillae).
Geography, cytology. Paleotropical and Australian. Old World tropical. Tropical Africa, India to Indochina, Malaya, Australia.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Lamiales. Cronquist’s Subclass Asteridae; Scrophulariales. APG (1998) Eudicot; core Eudicot; Asterid; Euasterid I; Lamiales (as a synonym of Acanthaceae). Species 90 (with Staurogyne and Elytraria included). Genera 3; Elytraria, Nelsonia, Staurogyne.
Supposedly intermediate between Acanthaceae and Scrophulariaceae. This description probably fails to cater adequately for Elytraria and Staurogyne.
Illustrations. • Technical details (Nelsonia).
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).
