Flora of North America species comparison

Rubus ulmifolius can be distinguished, especially from the closely related R. bifrons and R. vestitus, by its strongly pruinose stems, finely serrate leaflets, and lack of glands throughout. Unlike R. ulmifolius, strongly pruinose native Rubus species lack relatively large and showy pink petals. Some new stems developing from tip-rooting, and early leaves on such stems (especially in shade), are not whitened abaxially and are tomentose. Such unusual stems develop typical leaves and surfaces in parts formed later.

There has been nomenclatural confusion over unarmed plants of Rubus ulmifolius (see E. Monasterio-Huelin and H. E. Weber 1996). Rubus inermis Willdenow is an illegitimate later homonym of R. inermis Pourret, and the type specimens for both names are of poor-quality. If an unarmed variety of R. ulmifolius is to be recognized, such as occurs in California, the name var. anoplothyrsus Sudre should be used instead of var. inermis (Willdenow) Focke.

Rubus ulmifolius is attractive and is potentially weedy but relatively uncommon, found primarily in coastal California from the San Francisco Bay region southward. It probably no longer persists in New Jersey, last collected there in 1897, and it is rare in Nevada and Oregon. Rubus ulmifolius likely hybridizes with R. bifrons where they co-occur; it is one of relatively few diploid and sexually reproducing species of European blackberries.

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

Rubus pascuus is probably more widespread than indicated here. The species is most likely to be mistaken for R. bifrons, R. cuneifolius, or R. pensilvanicus. Unlike R. bifrons, R. pascuus is generally more densely glandular, has much shorter, compact inflorescences that usually barely surpass the leaves, and tends to hold its primocane leaves relatively erect (versus spreading in R. bifrons). Although both can be semievergreen, R. pascuus will lose its leaves more readily than R. bifrons in areas where they co-occur. When compared with R. cuneifolius, R. pascuus has pale pink to white petals and ovate to broadly elliptic leaflets with flat margins, the entire part restricted to the base; R. cuneifolius has white petals and cuneate to obovate leaflets with usually revolute margins, the proximal third entire. When compared with R. pensilvanicus, R. pascuus has pale pink to white petals. Rubus pensilvanicus only has white petals as well as abaxial leaf surfaces, which are white to gray-green in R. pascuus with dense, short-velutinous to tomentose indument, while those of R. pensilvanicus can be hairy but never whitish to gray-green. A notable aspect of R. pascuus is how vigorously armed it is, more so than most other Rubus species in the flora area.

Rubus pascuus may represent a stabilized hybrid between a European and a native blackberry species, suggested by whitish pubescence on the abaxial leaf surface and pale pink petals. L. H. Bailey placed R. pascuus in his sect. Cuneifolii (L. H. Bailey) L. H. Bailey, likely because of the whitish hairs on the abaxial leaf surface.

The use of the name Rubus pascuus here is tentative; it is the best fit to the material observed. This treatment follows H. A. Davis (1990) for the choice of the name to use and its associated synonymy.

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