Spathacanthus Baill. Hist. pl. 10: 444. 1891

Burgos-Hernandez, Mireya & Castillo-Campos, Gonzalo, 2020, Taxonomic revision of the Mesoamerican genus Spathacanthus (Justicieae, Acanthoideae, Acanthaceae), PhytoKeys 144, pp. 31-55 : 31

Spathacanthus Baill. Hist. pl. 10: 444. 1891

Type.

Spathacanthus hahnianus Baill.

Description.

Small trees or shrubs, highly branched. Stems sometimes with conspicuous lenticels. Leaves opposite, sessile, subsessile to petiolate, entire, blade usually elongated, oblong or elliptical, membranous. Inflorescence terminal, cymose in the form of a thyrse, with opposite branches, consisting of dichasia or monochasia when one of the buds aborts, sometimes axillary, sessile to pedunculate, subtended by a bract; bracts opposite, small, green, entire. Flowers large, few, subsessile to pedicellate, pedicels usually enlarged in fruit; 2 homomorphic bracteoles; calyx green or yellowish, spathaceous, bilabiate equally or unequally divided into 2 segments; anterior segment with 2 fused lobes, apically entire to bifid; the posterior segment with 3 fused lobes, apically entire to trifid; corolla white or yellow, externally glabrous; tube expanded distally into a distinct throat; corolla with upper lip deeply bilobed, lower lip deeply trilobed; corolla lobes imbricate in bud. Stamens 4, didynamous, adnate at base of corolla throat; anthers monothecous or dithecous, if dithecous, then thecae equal in size, parallel, equally inserted, lacking basal appendages; anterior pair dehiscing towards upper lip, posterior pair dehiscing towards lower lip; staminodes lacking. Style glabrous, included in corolla tube; stigma bilobed, lobes equal. Capsule stipitate, large, glabrous, woody, green when immature, brown when dry. Seeds 4, homomorphic, flattened, glabrous.

The genus Spathacanthus consists of four species occurring in humid tropical forests to temperate forests of south-eastern Mexico and Central America (Fig. 1A, B ). The genus is easily differentiated from other Acanthaceae genera by the spathaceous calyx divided into 2 segments. The extremely large fruits are also distinctive amongst Neotropical Acanthaceae .

Figures

Figure 1. Distribution of the Mesoamerican genus Spathacanthus Baillon. A Distribution of S. hahnianus and S. hoffmannii B distribution of S. magdalenae and S. parviflorus.