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.)