Tetrameriinae

Manzitto-Tripp, Erin A., Darbyshire, Iain, Daniel, Lucinda A. McDade Thomas F. & Kiel, Carrie A., 2022, Revised classification of Acanthaceae and worldwide dichotomous keys, TAXON 71 (1), pp. 103-153 : 141

Tetrameriinae T.F.Daniel, Kiel & McDade, subtr. nov. –

Type: Tetramerium Nees.

Perennial herbs or shrubs with cystoliths; leaves opposite; inflorescences in 1- to many-flowered dichasia, these borne in leaf axils or in axils of bracts along spikes, racemes, or thyrses, which are sometimes branched into panicles, flowers subtended by paired bracteoles, bracts and/or bracteoles inconspicuous or conspicuous; corollas variable in size, shape and color, rugula absent; androecium of 2 stamens and no staminodes (4 stamens in Chalarothyrsus ), anthers bithecous (monothecous in Clinacanthus ), thecae of a pair equally or subequally inserted on filament, parallel to sagittate, lacking basal appendages; stigma usually 2-lobed; capsule clavate, 2–4-seeded, retinacula present and usually not separating from inner capsule wall at maturity (separating slightly in Henrya and Tetramerium ); seeds distinct and expelled from capsule on dehiscence (indistinct by fusion with retinacula and capsule wall, and not expelled from capsule valves in Aphanosperma and Chalarothyrsus ); seeds compressed, surfaces and margin smooth or variously ornamented, trichomes usually absent (hygroscopic trichomes present in Henrya insularis ); pollen usually 3- colporate, 6-pseudocolpate (see Daniel & al., 2008 for rare variants).