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Rubus

See list of 28 species in this genus

Treatment of Rubus subgenus Rubus (i.e., the blackberries) varies greatly between different authors. At one extreme are treatments that recognize highly variable “megaspecies”, ignoring vast amounts of morphological diversity through the use of broadly defined taxa (e.g., Gleason and Cronquist 1991). At the other extreme are treatments that recognize a multitude of species, these often based on a single difference, such as more pointed leaflets or a more compact inflorescence (e.g., Davis et al. 1967, 1968a, 1968b, 1969a, 1969b, 1970). Followed here is Hodgdon and Steele (1966), a treatment of intermediate nature that provides names to some of the variation seen on the New England landscape. The species are, in most cases, defined on substantial differences in morphology (though some are undoubtedly arbitrary and seek to divide continuous variation). The work of Hodgdon and Steele appears to be the best compromise until a thorough biosystematic study is performed. The synonymy of the blackberries follows Hodgdon and Steele and should be considered tentative (as admonished by the authors). Further, preliminary work examining types suggest that some of these synonyms were incorrectly placed by them. In the key, distinguishing the types of stems is very important. Primocanes are the first-year stems and are green for the first half of the growing season, later forming winter buds at the tip. Floricanes are the second-year stems and are usually red or red-brown to purple or purple-brown and frequently have dead tips (i.e., no buds). Stem habit (e.g., ascending, doming, trailing) must be assessed on primocanes from the summer and fall (i.e., during or after flowering on the floricanes) for two important reasons. First, primocanes that may eventually become prostrate often grow upward during initial growth in the spring and do not arch over to the ground until summer. Second, various items can depress floricanes and make them appear decumbent (e.g., winter snow, fallen tree branches). Prickle stature is an important component of the identification key. The following measurements define terms used in the key: bristles are 0.1–0.4 (–0.5) mm thick at base, small-based prickles are (0.3–) 0.4–1 (–1.2) mm thick at base, and broad-based prickles are (0.8–) 1–4 mm thick at base. Many hybrid combinations between species of blackberries have been noted. Those in the R. flagellaris complex ( R. arenicola, R. enslenii, R. flagellaris, R. jaysmithii, R. recurvicaulis) would, in most cases, be so difficult to detect that not all the combinations that likely occur on the landscape are noted in the following text. Rubus parviflorus Nutt. was reported from MA by Kartesz (1999), but specimens are unknown and the record is likely erroneous. References: Hodgdon and Steele (1966), Steele and Hodgdon (1970).

  • 1a. Principal leaves simple; plants unarmed
  • 1b. Principal leaves compound; plants usually armed with prickles or stiff bristles (always unarmed in R. pubescens and sometimes unarmed in R. canadensis)
    • 5a. Stems herbaceous, not clearly differentiated into primocanes and floricanes, unarmed; stipules oblanceolate to obovate; fruit separating from the receptacle only with difficulty
    • 5b. Stems woody, clearly differentiated into primocanes and floricanes (except R. illecebrosus with annual, above-ground stems), usually armed with bristles or prickles; stipules linear or setaceous; fruit separating from the receptacle or not
      • 6a. Leaves with 3–9 pinnately arranged leaflets (sometimes palmately arranged in R. occidentalis); fruit red or black, separating from the dry receptacle, the receptacle remaining behind on the pedicel (separating from the pedicel with the fleshy receptacle in R. illecebrosus)
        • 7a. Petals large, surpassing the sepals; floricane leaves with 5–9 leaflets; leaflets glabrous on the abaxial surface; fruit red, not separating from the receptacle
        • 7b. Petals smaller, equaled or surpassed by the sepals; floricane leaves with 3 leaflets; leaflets densely tomentose with white-gray to gray hairs on the abaxial surface; fruit red or black, separating from the receptacle
          • 8a. Fruit purple-black (rarely yellow), the individual drupes separated by bands 
of tomentum; pedicels with only moderately stout, often curved, prickles [Fig. 868]; primocanes very glaucous
          • 8b. Fruit red to orange (rarely yellow), the individual drupes not separated by bands of tomentose pubescence; pedicels with straight bristles or minute prickles and often also glandular hairs; primocanes not, or only slightly, glaucous
            • 9a. Rachis of inflorescence, pedicels, and often also the primocanes with stipitate glands or glandular bristles
              • 10a. Petals white or pink, erect and incurved, appressed to the stamens; pedicels and calyx densely beset with elongate, red to purple, gland-tipped bristles 3–5 mm long [Fig. 869]; primocanes arching to doming, sometimes rooting at the tip
              • 10b. Petals white, ascending to erect, but not appressed to the stamens; pedicels and calyx with minute, stipitate glands, these often exceeded by eglandular bristles; primocanes erect to arching, not rooting at the tip 
 (in part)
            • 9b. Rachis of inflorescence, pedicels, and primocanes eglandular
              • 11a. Petals white, ascending to erect, but not appressed to the stamens; terminal leaflet acute to acuminate at the apex; endocarps shallowly pitted 
 (in part)
              • 11b. Petals pink to purple-red, erect and incurved, appressed to the stamens; terminal leaflet obtuse to broad-acute at the apex; endocarps shallowly rugose
      • 6b. Leaves with 3 pinnately arranged or 5 palmately arranged leaflets; fruit black at maturity, separating from the pedicel with the fleshy receptacle
        • 12a. Inflorescence a panicle, the branches and pedicels armed with stout, 
flattened prickles [Fig. 864]; coarse, scrambling and climbing plants armed with 
stout, flattened prickles
        • 12b. Inflorescence a raceme, corymb-like raceme, or rarely a solitary flower, the branches and pedicels usually unarmed (never with stout, flattened prickles) [Figs. 863,866,867]; upright to trailing plants with weak to strong armature, the prickles usually ± terete above the base
          • 15a. Primocanes doming, prostrate, or trailing, rooting, or with the opportunity to root, at the tip (in some species the depressed forms of the primocane not developing until midsummer when the apex of the stems finally reaches the ground) [Fig. 867]
            • 16a. Primocanes armed with hairs, bristles, or slender, small-based prickles [Fig. 867]; petals 5–12 mm long; leaves usually lustrous, tending to be evergreen, with 3 leaflets 3.5–5 (–7) cm long
            • 16b. Primocanes armed, at least in part, with stout, broad-based prickles 
 [Fig. 865]; petals 10–25 mm long; leaves lustrous to, more commonly, dull, usually deciduous, with 3 or 5 leaflets 6–15 (–16) cm long (2–5 cm long 
in the rare R. cuneifolius)
              • 17a. Inflorescence with 1–4 (–5) flowers [Fig. 866]; pedicels ± erect, 10–60 (–80) mm long, the uppermost one 10–20 mm long (or the peduncle to 50 mm when only 1 flower is present) [Fig. 866]
                • 18a. Stems very slender, 1–2 mm in diameter, with prickles (0.5–) 1–2 mm long; primocane leaves usually with 3 leaflets; inflorescences with 1 (–3) flowers
                • 18b. Stems thicker, 1.5–4 mm in diameter, with prickles 1–3 (–4) mm long; primocane leaves with 3 or 5 leaflets; inflorescences with 1–4 (–5) flowers
                  • 19a. Leaf blades ± glabrous abaxially, the hairs, when present, essentially confined to the leaflet midribs and primary lateral veins, usually not noticeable to the touch
                  • 19b. Leaf blades ± evidently pubescent abaxially, with hairs present across the surface (i.e., between the primary lateral veins), usually noticeable to the touch
              • 17b. Inflorescence with (1–) 2–8 (–12) flowers; pedicels ascending to spreading, 5–40 mm long, the uppermost one 3–11 (–15) mm long
                • 20a. Leaf blades ± glabrous abaxially, the hairs, when present, essentially confined to the leaflet midribs and primary lateral veins, usually not noticeable to the touch; inflorescence rachis and pedicels sparsely to moderately pubescent
                • 20b. Leaf blades ± evidently pubescent abaxially, with hairs present across the surface (i.e., between the primary lateral veins), usually noticeable to the touch; inflorescence rachis and pedicels moderately to densely pubescent
          • 15b. Primocanes arching or erect, not rooting at the tip (sometimes doming in 
 R. vermontanus)
            • 21a. Primocanes armed with hairs, bristles, or slender, small-based prickles 
 [Fig. 870]; stems 0.3–1 m tall; axis of inflorescence commonly with stipitate-glands (always lacking in R. elegantulus and often lacking in R. semisetosus)
              • 22a. Leaf blades ± evidently pubescent abaxially, with hairs present across the surface (i.e., between the primary lateral veins), usually noticeable to the touch; primocanes armed, at least in part, with slender, small-based prickles
              • 22b. Leaf blades ± glabrous abaxially, the hairs, when present, essentially confined to the leaflet midribs and primary lateral veins, usually not noticeable to the touch; primocane armature various
            • 21b. Primocanes armed, at least in part, with stout, broad-based prickles; stems 0.5–3 m tall; axis of inflorescence lacking stipitate-glands except in R. allegheniensis and hybrids with that species
              • 25a. Inflorescence, and often also the primocane, pubescent with 
stipitate glands [Fig. 863], the inflorescence (3–) 8–20 cm long and with (3–) 9–22 flowers
              • 25b. Inflorescence and primocane ± lacking stipitate glands, the inflorescence 3–11 (–17) cm long and with (2–) 3–15 (–21) flowers
                • 26a. Leaf blades ± glabrous abaxially, the hairs, when present, essentially confined to the leaflet midribs and primary lateral veins, usually not noticeable to the touch
                  • 27a. Prickles of the stem absent or few, numbering 0–10 per 10 cm; inflorescence rachis pubescent to subglabrous, usually without prickles
                  • 27b. Prickles of the stem more numerous, numbering 10–60 (–100) per 10 cm [Fig. 865]; inflorescence rachis pubescent, often with thin prickles (in part)
                • 26b. Leaf blades ± evidently pubescent abaxially, with hairs present across the surface (i.e., between the primary lateral veins), usually noticeable to the touch
                  • 28a. Leaflets oblanceolate to obovate, definitely widest above the middle, densely tomentose abaxially with white to gray hairs (sometimes becoming partly glabrate in late season)
                  • 28b. Leaflets elliptic or elliptic-oblanceolate to broad-ovate, 
widest near or below the middle, pubescent abaxially, but not 
densely tomentose
                    • 29a. Terminal leaflet of primocane leaves elliptic-oblanceolate to elliptic, cuneate to narrow-rounded at the base, 2 or more times as long as wide
                    • 29b. Terminal leaflet of primocane leaves ovate to broad-ovate, broad-cuneate to cordate at the base, less than 2 times as long 
as wide
                      • 30a. Prickles of the stem mostly 2–4 mm long, numbering 
0–20 per 10 cm; leaf blades herbaceous; inflorescence with 
(0–) 1 or 2 (–6) leafy bracts (i.e., most of the pedicels subtended by small, stipule-like bracts)
                      • 30b. Prickles of the stem mostly 4–6 mm long, numbering 4–60 per 10 cm; leaf blades tending to be more chartaceous; inflorescence with (0–) 1–7 leafy bracts (i.e., many of the pedicels subtended by foliaceous bracts)

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