Flora of North America species comparison

Species 22 (4 in the flora).

Barbarea is a difficult genus much in need of systematic and phylogenetic studies throughout its range. Although some of its species are easily recognizable, some complexes, especially the widespread or weedy taxa, remain problematic. It is likely that hybridization is involved, but no studies have confirmed that.

The determination of flowering material is not always possible, and most workers have relied heavily on the distalmost leaves to separate species. Both Barbarea orthoceras and B. verna are said to have pinnatisect to pinnatifid distalmost leaves, whereas B. stricta and B. vulgaris are said to have undivided, entire, or dentate leaves. This separation can be misleading because B. orthoceras sometimes has entire or dentate distal leaves, whereas in some B. vulgaris the distal leaves are deeply divided. In B. vulgaris, the style length and its thickness in relation to the fruits are useful in separating it from the remaining species, though, on rare occasions, both B. orthoceras and B. stricta have slender styles to 2 mm. In these cases, both B. orthoceras and B. stricta can be separated from B. vulgaris by the ciliate auricles of cauline leaves and subapically pubescent sepals. Both sepals and auricles of distalmost leaves are always glabrous in B. vulgaris. Although all the Eurasian specimens of B. stricta that I examined have pubescent auricles and sepal apices, the number of trichomes can be quite variable and ranges from one to many. Most of the naturalized North American plants of B. stricta have glabrescent or glabrous sepals. However, that species can be further distinguished by having petals 2.5–4.5 × 0.5–1(–1.2) mm, the smallest and narrowest among the four species growing in North America. In the absence of mature fruits, one needs to be aware of the variation in the other characters.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

M. L. Fernald (1909) treated some plants of Barbarea stricta as B. vulgaris var. longisiliqua Carion. Although G. A. Mulligan (1978) was the first to record B. stricta for North America, neither his record nor the species was accounted for by R. C. Rollins (1993). Forms of B. vulgaris with fruits appressed to rachis can easily be confused with B. stricta and some forms of B. orthoceras. The latter is separated from both B. stricta and B. vulgaris by having distalmost cauline leaves either pinnatifid or with at least a pair of well-developed lateral lobes. The distalmost leaves in both B. stricta and B. vulgaris have margins entire or obscurely to coarsely dentate. Barbarea stricta has shorter petals (2.5–4.5 mm) and styles (0.2–1.5(–2) mm), strictly erect and straight fruiting pedicels, and sepals and auricles of distalmost leaves often with a few apical hairs. By contrast, B. vulgaris has longer petals [(5–)6–9(–10) mm] and styles [(1–)1.5–3(–3.5) mm], erect or widely spreading and often curved fruiting pedicels, and glabrous sepals and leaf auricles. The boundaries between the two species can be somewhat blurred in parts of New England, and it is not known if hybridization is involved. In that region, plants of B. stricta tend to have slightly longer styles (to 2 mm), and the number of hairs at the auricle apices can be reduced to one and those of the sepals can be absent.

(Discussion copyrighted by Flora of North America; reprinted with permission.)