Rubus ulmifolius
Rubus caesius
elm-leaf blackberry
European dewberry
biennial, erect, then arching, usually moderately, rarely sparsely, hairy hairs stellate, eglandular, strongly pruinose;
prickles absent or sparse to dense, erect to hooked, stout, 3–10 mm, broad-based.
biennial, creeping or arching then creeping, glabrous or hairy, eglandular or sparsely sessile- to short-stipitate-glandular, strongly pruinose;
prickles sparse to dense, erect to retrorse, slender, 1–3 mm, narrow- or broad-based.
persistent or nearly so, ternate to palmately compound;
stipules filiform to linear, 4–12 mm;
leaflets 3–5, terminal ovate, elliptic, or suborbiculate to obovate, 4–10 × 2–6(–9) cm, base rounded to cuneate, unlobed, margins finely to moderately serrate, apex acute or acuminate to attenuate, abaxial surfaces with hooked prickles on larger veins, densely white short-velutinous, hairs usually minute, eglandular.
deciduous, ternate;
stipules linear-lanceolate to ovate, 5–15 mm;
terminal leaflets ovate, 4–14 × 3–10 cm, base rounded to shallowly cordate, unlobed or shallowly lobed, margins coarsely serrate to doubly serrate, apex acute to acuminate, abaxial surfaces with prickles on midveins or unarmed, sparsely to moderately hairy, eglandular or sparsely short-stipitate-glandular along larger veins.
terminal, 10–60-flowered, paniculiform or thyrsiform.
terminal on short shoot, usually appearing axillary, 1–6-flowered, solitary flowers, cymiform, or racemiform.
unarmed or prickles moderate to dense, erect to hooked, densely short-hairy, eglandular.
unarmed or prickles sparse to dense, erect to retrorse, densely hairy, sparsely to densely sessile- to short- or long-stipitate-glandular.
bisexual;
petals usually pink, sometimes white, obovate or elliptic to suborbiculate, 5–12 mm;
filaments filiform;
ovaries apically hairy.
bisexual;
petals white, obovate to elliptic or suborbiculate, 7–13 mm;
filaments filiform;
ovaries glabrous.
black, globose to ovoid, 1–1.5 cm;
drupelets 10–40, strongly coherent, separating with torus attached.
appearing bluish, black beneath bloom, pruinose, globose, 0.5–1.5 cm;
drupelets 1–5(–20), weakly coherent, separating with torus attached.
= 14.
= 28.
Rubus ulmifolius
Rubus caesius
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.)
Within the flora area, Rubus caesius usually produces fruit with few, relatively large drupelets; in Eurasia, fruit with more drupelets are typical, and weakly pruinose fruit have been observed.
Rubus caesius is vegetatively similar to R. flagellaris and is introduced into parts of the geographic range of the latter; see M. P. Widrlechner (1998) for a comparison of these two species. Rubus caesius shows striking vegetative similarity to pruinose, trifoliate-leaved plants of R. ursinus, with which it may have a close relationship (L. A. Alice, unpubl.). In the absence of flowers or fruit, these two species could be mistaken for one another. Rubus caesius generally has broader middle primocane leaflets than R. ursinus, but that is not a consistent difference. Rubus caesius may have been introduced into the geographic range of R. ursinus; most herbarium specimens surveyed have been inadequate to make a proper determination. On specimen labels, herbarium collectors should describe at least the color of the fruit. In the last decade, R. caesius apparently has become much more aggressive around Ithaca, New York, despite occurring there since the early twentieth century (F. R. Wesley, pers. comm.).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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