Hybanthus

Herbs or subshrubs, annual or perennial, [subshrubs, shrubs], caulescent, homophyllous, glabrous or hairy. Stems persistent, 1–20, usually erect, sometimes suberect or prostrate, leafy, simple or branched, from thick, fleshy or subligneous, branched or unbranched rhizome or taproot. Leaves cauline, simple, proximal usually opposite, distal usually alternate, petiolate or sessile; stipules not adnate to petiole, linear-subulate to leaflike, usually shorter than leaves; blade not overlapping basally, linear, lanceolate to oblanceolate, ovate to obovate, or elliptic, surfaces not mottled. Inflorescences axillary in leaf axils, 1–3(4)-flowered or in poorly defined racemes; peduncle jointed; bracteoles present or absent. Flowers: sepals subequal, not auriculate; upper 2 and lateral 2 petals not showy, 0.5–5 mm, lowest petal showy, larger than others, narrowed at middle, angular-deltate, elliptic, oblong, orbiculate, or ovate, upper and lateral petals usually glabrous, lower sometimes bearded adaxially; spur gibbous; stamens connate, lowest 2 filaments not spurred with nectary; cleistogamous flowers present or absent. Capsules ovoid, globose, obtusely trigonous, oblong, or ellipsoid, glabrous. Seeds (3–)6–9, globose to slightly flattened, glabrous [hairy], with whitish elaiosome. x = 4.

Distribution

North America, Mexico, West Indies, Central America, South America, Asia, Africa, Australia, tropical and subtropical areas.

Discussion

Species 100–115 (5 in the flora).

In 2010, M. N. Seo et al. concluded that polyploidy likely played a role in speciation in Hybanthus and Seo et al. (2011) proposed an infrageneric classification of Hybanthus based on foliar micromorphology. Research using trnL/trnL–F and rbcL plastid regions shows that Hybanthus is polyphyletic and can be segregated into nine morphologically and biogeographically distinct groups (G. A. Wahlert et al. 2014). Molecular phylogenetic and morphological evidence will be used to circumscribe the nine Hybanthus lineages as separate genera (Wahlert et al.). Hybanthus would be reduced to two or three species and H. concolor would be placed in Cubelium (H. E. Ballard, pers. comm.), a position supported in some molecular studies, for example, T. Marcussen et al. (2010). The other four species in the flora area would be placed in Pombalia (Ballard, pers. comm.).

The overall outline of the lowest petal (sometimes referred to as the anterior petal) is usually pandurate or panduriform and is one of the more diagnostic characters of Hybanthus. The distal limb is usually enlarged and is longer and wider than the upper and lateral petals. The distal limb of some species rolls inward after anthesis.

The method by which capsules dehisce is not discussed in the major references that treat Hybanthus. Because of the similarity to Viola capsules, it may be assumed that their dehiscence is similar. Although capsules of Viola are sometimes described as “explosively dehiscent,” the capsules of at least some North American species open relatively slowly. As the capsule

valves dry out, they contract and squeeze the seeds causing them to be ballistically ejected. J. de Paula-Souza (pers. comm.) reported that Violaceae capsules in South America are not truly “explosive,” but rather the seeds are expelled as the capsule valves dry out.

Selected References

Morton, C. V. 1944. Studies of tropical American plants. The genus Hybanthus in continental North America. Contr. U.S. Natl. Herb. 29: 74–82.

Morton, C. V. 1971. Some types and range extensions in Hybanthus (Violaceae). Phytologia 21: 56–62.

Lower Taxa

Hybanthus attenuatus, Hybanthus concolor, Hybanthus linearifolius, Hybanthus parviflorus, Hybanthus verticillatus

Key

1	Seeds white to cream.	Hybanthus concolor
1	Seeds dark brown to black with white to gray mottling, brownish black to black, or shiny black	> 2
2	Leaf margins crenate to serrate	> 3
2	Leaf margins entire or remotely crenulate-dentate	> 4
3	Leaf blades 1.5–7(–10.5) cm; petioles (3–)4–7 mm; petals white, purple-tinged, or violet, lowest petal 8–12 mm; bracteoles present; Arizona.	Hybanthus attenuatus
3	Leaf blades 0.3–3 cm; petioles 0.5–4 mm; petals white, lowest petal 1.5–3.7 mm; bracteoles absent; Georgia, New Jersey.	Hybanthus parviflorus
4	Lowest petal 5–9.5 mm, limb 4–10 mm wide, with basal purple patch.	Hybanthus linearifolius
4	Lowest petal 2.5–6 mm, limb 1–3 mm wide, without basal purple patch.	Hybanthus verticillatus