Rubus caesius, L.

75. R. caesius L. View in CoL , Sp. Pl. 493 (1753) View Cited Treatment .

Stems flagelliform, branched, terete, glabrous, pruinose, rarely with a few short glands; prickles few or many, weak, short, straight or falcate. Leaves ternate, slightly hairy above, more or less pubescent be­ neath; terminal leaflet ovate, sometimes more or less 3-lobed, shortly acuminate, subcordate, rather coarsely biserrate; lateral leaflets often bilobed; petiole sulcate; stipules ovate-lanceolate. Inflorescence short, consisting of a terminal and a few axillary 2- to 5-flowered corymbs; pedicels long, with short hairs, fine glands and sparse prickles; flowers 2-2-5 cm in diameter. Sepals appressed to the developing fruit, ovate-lanceolate, shortly acuminate, grey-green tomentose, with white margin and short glands; petals large, ovate, elliptical or suborbicular, white; stamens green, equalling the greenish styles. Drupelets 2-20, large, black, pruinose, loosely coherent. 2zi = 28. Somewhat calcicole. Most of Europe. All except Az Co Cr Fa Is Sa Sb Tu.

Several varieties have been described, some with pink flowers.

Hybrids between R. caesius and plants belonging to other sub­ sections of Rubus are termed Rubi Corylifolii. Many well-defined taxa have been described but they tend to have very re­ stricted distributions and are not listed here; in Belgium for example, 38 Corylifolii have been described, in Britain 20, in Switzerland 50 and in Romania 28. Corylifolii are recognised by having at least some of the following characters; stems terete; stipules more or less lanceolate; leaves large; leaflets imbricate, the basal subsessile; inflorescence short and broad, or narrow and with few-flowered branches; flowers long-stalked; petals large, orbicular; drupelets large, partly abortive, rather pruinose. Some set good fruit consisting of large but few drupelets, whilst others tend to be somewhat infertile. In Great Britain and Scan­ dinavia the chromosome numbers of many of the Rubi Corylifolii are higher than in the plants of other subsections (counts of 35 or 42 are relatively common), and this may well be true of the Corylifolii in other countries. Many are characteristic of ground which has been disturbed; they are particularly common at the edge of cultivated fields, in hedges, along ditch-banks, forest roads etc. The names R. corylifolius Sm. and R. dumetorum Weihe are no longer in use except as referring to rather broad aggregates.