| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Nelsoniaceae Sreem.

~ Acanthaceae, cf. Nelsonioideae.

Habit and leaf form. Herbs. Hydrophytic (Staurogyne spp.), or helophytic, or mesophytic (?). Leaves opposite; simple. Lamina entire. Leaves exstipulate.

Leaf anatomy. Cystoliths absent. The mesophyll without sclerenchymatous idioblasts.

Axial (stem, wood) anatomy. Internal phloem present. Secondary thickening developing from a conventional cambial ring.

‘Included’ phloem absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. 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; blunt-lobed and toothed (the lower lobe bifid, the other 4 blunt); 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 2 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, phytochemistry. Not cyanogenic. Iridoids detected (in Nelsonia); ‘Route II’ type (normal and decarb.).

Special distinguishing 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 III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Lamiales (as a synonym of Acanthaceae).

Species 90 (with Staurogyne and Elytraria included). Genera 3; Elytraria, Nelsonia, Staurogyne.

General remarks. Long supposed to be intermediate between Acanthaceae and Scrophulariaceae. Other than ‘esoteric characters’ of doubtful taxonomic significance in view of limited sampling, viz., leaf lamina with cystoliths and ovule with undifferentiated endothelium, Nelsoniaceae seem to differ from Acanthaceae sensu stricto (q.v.) only in the regular corolla and unspecialised seed funicles. Furthermore, this compilation probably fails to cater adequately for Elytraria and Staurogyne.

Illustrations. • Nelsonia brunellioides: Nat Pflanzenfam. iv (1895). • Le Maout and Decaisne: Nelsonia canescens, as N. campestris: Lindley. • Elytraria imbricata: Burger, Fl. Costaricensis 18 (1986).

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: 8th June 2026. delta-intkey.com’.

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