Violaceae
Hybanthus
violet family
greenviolet
0–20, prostrate to erect.
persistent, 1–20, usually erect, sometimes suberect or prostrate, leafy, simple or branched, from thick, fleshy or subligneous, branched or unbranched rhizome or taproot.
cauline or basal, (attached directly to rhizome, some Viola), alternate (and opposite in Hybanthus [and other genera]), simple or compound, stipulate [estipulate], petiolate or sessile;
blade unlobed or lobed.
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.
1(–4)[–5]-flowered, axillary from leaf axils or scapose from rhizomes or stolons (or in racemes of umbels), pedunculate;
bracteoles usually present on peduncles, usually alternate.
axillary in leaf axils, 1–3(4)-flowered or in poorly defined racemes;
peduncle jointed;
bracteoles present or absent.
bisexual [unisexual, plants dioecious], perianth and unequal, imbricate in bud [convolute], lowermost petal often larger with gibbous or elongated spur;
stamens 5, alternate with petals, surrounding ovary, connivent or syngenesious;
filaments 0–1 mm, filaments of 2 anterior stamens often with nectaries protruding into spur, anther dehiscence by longitudinal slits;
pistil 1, [2–]3[–5]-carpellate;
ovary superior, 1-locular;
placentation parietal;
ovules [1–2]8–75, anatropous, bitegmic, crassinucellate;
style [0–]1, usually enlarged distally, solid or hollow;
stigma 1 [3–5], with or without hairs.
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.
capsular [berry, nut], 3-valved, dehiscence loculicidal.
ovoid, globose, obtusely trigonous, oblong, or ellipsoid, glabrous.
[1–](3–)6–75, hard, embryo not developed at time of dispersal, spheroid or ovoid [strongly flattened], glabrous [hairy], some arillate, some with elaiosome [seeds winged in some woody vines].
(3–)6–9, globose to slightly flattened, glabrous [hairy], with whitish elaiosome.
= 4.
Violaceae
Hybanthus
Genera 23, species 1000–1100 (2 genera, 78 species in the flora).
The Violaceae is predominantly tropical with worldwide distribution. Most genera are monotypic or oligotypic and are restricted to the New World or Old World tropics (H. E. Ballard et al. 1998; G. A. Wahlert et al. 2014). Except for Viola, Hybanthus, and Rinorea, which together account for 98% of all species in the family, most genera are limited to one continent or island system (M. Feng 2005).
Violaceae has been placed in the Violales by most authors (A. Cronquist 1981; R. F. Thorne 1992; A. L. Takhtajan 1997). Based on data from cladistic analyses, it was included in the Malpighiales in 1998 (Angiosperm Phylogeny Group 1998, 2003, 2009).
The Malpighiales clade was first identified by M. W. Chase et al. (1993) in a phylogenetic analysis of nucleotide sequences from the plastid gene rbcL (K. J. Wurdack and C. C. Davis 2009). Currently, 35 families are included in Malpighiales (Angiosperm Phylogeny Group 2009). Molecular studies employing multiple gene regions have confirmed the monophyly of Malpighiales, which includes about 16,000 species (Wurdack and Davis). Relationships within Malpighiales remain poorly understood and it is the most poorly resolved large rosid clade (Wurdack and Davis).
Violaceae were previously organized into three subfamilies, Fusispermoideae, Leonioideae, and Violoideae (W. H. A. Hekking 1988; S. A. Hodges et al. 1995). Evidence confirms that Fusispermum is basal in Violaceae and belongs in the monotypic subfamily Fusispermoideae (M. Feng 2005; T. Tokuoka 2008) and Leonioideae should be subsumed in Violoideae (Feng; Feng and H. E. Ballard 2005; Tokuoka). All genera in Violaceae except Fusispermum are currently included in the subfamily Violoideae. Usually described as having an actinomorphic corolla, the calyx and corolla of Fusispermum were reported to actually be weakly zygomorphic (G. A. Wahlert et al. 2014).
W. H. A. Hekking (1988) divided subfamily Violoideae into two tribes, Violeae and Rinoreeae. Viola and Hybanthus, the only two genera in the flora area, are placed in the Violeae.
In a study of Violaceae based on plastid and nuclear DNA sequences (rbcL, atpB, matK, and 18s rDNA), T. Tokuoka (2008) found that monophyly of the family is strongly supported. A study of 39 species of Viola occurring primarily in China using chloroplast sequences trnL-trnF, psbA-trnH, rpL16, and ITS showed that “subgenus” Viola is not monophyletic (Liang G. X. and Xing F. W. 2010). Their data imply that 1) erect stems may be more primitive than stolons or rosettes, 2) species with stigmatic beaks might have been trends in sections Trigonocarpae and Adnatae, respectively.
A study of Violaceae based on plastid DNA sequences showed that most intrafamilial taxa from previous classifications of Violaceae were not supported, that previously unsuspected generic affinities were revealed, and that reliance on floral symmetry (that is, actinomorphy versus zygomorphy) alone provides misleading inferences of relationships and heterogeneous generic circumscriptions (G. A. Wahlert et al. 2014).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants caulescent; sepals not auriculate; upper 2 and lateral 2 petals not showy, 0.5–5 mm; lowest petal showy, narrowed at middle; stamens connate, lowest 2 filaments not spurred with nectary; seeds (3–)6–9. | Hybanthus |
1. Plants caulescent or acaulescent; sepals auriculate; upper 2 and lateral 2 petals showy, 5+ mm; lowest petal showy, not narrowed at middle; stamens connivent, but distinct, lower 2 filaments spurred with nectary that protrudes into petal spur; seeds 6–75. | Viola |
1. Seeds white to cream. | H. 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. | H. 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. | H. parviflorus |
4. Lowest petal 5–9.5 mm, limb 4–10 mm wide, with basal purple patch. | H. linearifolius |
4. Lowest petal 2.5–6 mm, limb 1–3 mm wide, without basal purple patch. | H. verticillatus |
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