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Although Rubus includes many cultivated berry species, other commonly cultivated berries that do NOT belong to this genus are strawberries (Fragaria spp., also in the Rosaceae), blueberries cranberries, and lingonberries (Vaccinium spp., in the Ericaceae); huckleberries (Gaylusaccia species, in the Ericaceae), and gooseberries (Ribes species, related to currants, in the Grossulariaceae or Saxifragaceae).
Rubus species are botanically complex and often difficult to classify, as many species readily hybridize readily, and they are also characterized by apomixis (asexual reproduction), which leads to the persistence of many clonal lines that may appear to be separate species. Among this large group of species there is considerable variation in form, but in general they have erect, climbing, arching, or prostrate stems, in most species woody although herbaceous in a few; stems may be hairy or glabrous (smooth) or sometimes glaucous (waxy), and usually with prickles or bristles (hence the common name, brambles). The leaves are alternate and usually palmately or pinnately compound but occasionally simple, often toothed; leaves may be glabrous or hairy, sometimes with bristles or glandular hairs. Most Rubus species are biennials, with first year canes (primocanes) that have leaves only, while flowers and fruit develop on the second-year canes (floricanes). Leaf characters may vary from first to second year, which further complicates species recognition and classification.
Flowers, which are usually bisexual, are white, pink, or red, generally with 5 petals, and often occur in clusters but are occasionally solitary. The fruit is not botanically a berry, but is an aggregate of drupes or achenes—a compound fruit that develops from a single flower and composed of many smaller drupes (fleshy pulp surrounding a hard seed) or achenes (small, hard-coated fruits with skins that do not split open to reveal the seed when mature). The drupelets or achenes are aggregated on semispherical, conical, or cylindrical torus-shaped receptacle, from which the fruit may separate when it is picked or falls, leaving behind a hollow (as in raspberries); or the receptacle may remain attached to the fruit (as in blackberries).
(Bailey et al. 1976, FAOSTAT 2012, Flora of China Hedrick 1919, Martin et al. 1951, Michigan Flora Online 2011, van Wyk 2005.)