Trichanthera Kunth

Daniel, Thomas F., 2015, Synopsis of Trichanthera (Acanthaceae: Ruellieae: Trichantherinae), Proceedings of the California Academy of Sciences 62 (1), pp. 1-23 : 4-5

Trichanthera Kunth in Humboldt, Bonpland and Kunth, Nova Gen. Sp. 2:243.

1818 (“1817”)

(non Ehrenberg 1829).

TYPE.— Trichanthera gigantea (Bonpl.) Nees

(≡ Ruellia gigantea Bonpl. )

Trixanthera Raf., Sylva Tell. 146. 1838. TYPE.— Trixanthera angularis Raf. , nom. illeg.

(≡ Ruellia gigantea Bonpl. )

Shrubs or medium-sized trees with cystoliths, sometimes with multiple trunks and prop roots. Young stems quadrate-sulcate, often with warty or blisterlike tubercles on surface. Leaves opposite, petiolate, the pair at a node equal or usually unequal in size, blades subcoriaceous. Inflorescence of terminal thyrses (i.e., bearing pedunculate dichasia with pedicellate flowers) or, when branched, a terminal panicle of thyrses; each dichasium + peduncle subtended by a bract, each flower + pedicel subtended by 2 homomorphic bracteoles. Calyx deeply 5-lobed, lobes homomorphic or heteromorphic (4+1), imbricate during anthesis, sometimes elongating in fruit. Corolla ± campanulate, internally ± waxy or glossy, externally densely pubescent (except for proximal portion), tube funnelform with narrow proximal portion subcylindric and throat ampliate, limb 2-labiate or appearing ± actinomorphic, upper lip 2-lobed, lower lip 3-lobed, corolla lobes contorted in bud. Stamens 4, in two pairs, each pair consisting of a longer and a shorter stamen that are fused proximally, inserted at or near base of throat, exserted from mouth of corolla, extending beyond lips of corolla, longer stamen of each pair posterior and central in display of stamens, anthers 2- thecous, thecae of a pair equally inserted, parallel to subsagittate, rounded at base, lacking appendages, dehiscing toward lower lip (i.e., flower nototribic), pollen loxodicolporate. Style exserted from mouth of corolla, extending beyond lips, stigma asymmetric, usually exserted beyond anthers, 1 lobe ± vestigial. Capsule ellipsoid, estipitate, bearing retinacula. Seeds up to 10 per capsule, lenticular, surfaces smooth, shiny, and lacking trichomes.

The genus consists of two species and is native to southern Central America ( Panama) and northern South America ( Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela). Both species occur in moist to wet forests.

The generic name Trichanthera is nearly universally cited as having been published by Kunth in Humboldt, Bonpland, and Kunth’s Nova Genera et Species Plantarum vol. 2, on page 243 (the quarto edition was published earlier, in February, than the folio edition, which was published in June, of 1818; the publication date listed on the printed copies was “1817;” Stafleu and Cowan 1979). In this publication, Kunth indicated that Ruellia gigantea , “certe distincti generis ob stamina exserta, antheras pilosas et capsulae loculos dispermos. Fortasse Trichanthera nominandum.” Thus, he was indicating that the species was deserving of generic status and proposed “ Trichanthera ” as a possible name, but did not accept it in this publication. In 1829, Ehrenberg published Trichanthera Ehrenb. for an Old World genus of Zygophyllaceae (subsequently treated in Malvaceae and Sterculiaceae ). This name has been treated as illegitimate due to the prior existence of Kunth’s name. Eurynema Endl. was proposed by Endlicher (1842) as a new name for Ehrenberg’s “illegitimate” name, but no combination was made for the sole species, T. modesta Ehrenb. , which is now known as Hermannia modesta (Ehrenb.) Mast. (the combination for this name was effected by Masters in 1868, where the combination was attributed to Planchon, who instead made the combination Mahernia modesta (Ehrenb.) Planch. in 1855; Mahernia L. is sometimes treated as a synonym of Hermannia ). However, if Kunth’s name was not validly published, Trichanthera Ehrenb. becomes legitimate; it is currently treated as a heterotypic synonym of Hermannia L. The next generic name proposed for the acanthaceous species treated by Kunth was Trixanthera Raf. , proposed by Rafinesque (1838) specifically for Ruellia gigantea , to which species he gave the name T. angularis Raf. If Kunth’s generic name had been validly published, Trixanthera would be a synonym of it and Trixanthera angularis would be an illegitimate name and synonym of Trichanthera gigantea . Apparently, the first publication of the acanthaceous genus Trichanthera was that of Meisner (1840), who attributed the generic name to Kunth, but provided his own description. In 1847, Nees made the combination for the type, T. gigantea (Bonpl.) Nees

From the preceding summary, it is clear that Trichanthera Kunth is not validly published and that Trichanthera Ehrenb. has priority over Trichanthera Meisn. Without proactive nomenclatural actions (e.g., conservation), the oldest legitimate name for the genus containing Ruellia gigantea is Trixanthera Raf. , and new combinations for R. gigantea and T. corymbosa in that genus would be necessary. It might be argued that Rafinesque’s name should be considered an orthographic error (“trich” refers to hairs, “trix” refers to three-fold) for Kunth’s name, and that he was, in effect, validating Kunth’s proposed name. Were it not for Ehrenberg’s publication of Trichanthera for the sterculiaceous genus nine years before Rafinesque’s publication, this might have been a fortuitous argument to preserve the original spelling of Kunth’s name.

A proposal for conservation of the acanthaceous name Trichanthera is currently being prepared for submission to the Nomenclature Committee for Vascular Plants of the International Association for Plant Taxonomy. Although incorrect, the traditional author citation for the genus is used herein in accordance with Recommendation 14A.1 of McNeill et al. (2012).

Key to the Species of Trichanthera

1a. Thyrse usually corymbose; calyx 14–24 mm long during anthesis, lobes heteromorphic with 1 lobe conspicuously longer and wider (ca. 1.5 × or more wider) than others, the four similar lobes linear to linear-elliptic to linear-lanceolate, 2–4 mm wide, acute at apex; bracteoles and secondary bracteoles oblanceolate to linear, 4–12 (–25) mm long......... 1. T. corymbosa

1b. Thyrse elongate; calyx 6–13 mm long during anthesis, lobes homomorphic and ± equal in size, ovate-elliptic to elliptic, 3.5–7. 3 mm wide, rounded at apex; bracteoles and secondary bracteoles triangular, 2–4 mm long........................................ 2. T. gigantea