The Roseae comprise the large genus Rosa (15o species), char acterized by a more or less urn-shaped torus enclosing the numer ous carpels which form dry one-seeded fruits enveloped in the bright-coloured fleshy torus. The plants are shrubs bearing prickles on the stems and leaves; many species have a scrambling habit resembling the brambles. The , species of Rosa, like those of Rubus, are extremely variable, and a great number of subspecies, varieties and forms have been described. Petals are often wanting, as in Alchemilla (lady's mantle) and Poterium, and the flowers are often unisexual and frequently wind-pollinated, as in salad burnet (Poterium Sanguisorba), where the small flowers are crowded in heads, the upper pistillate, with protruding feathery stigmas, and the lower staminate (or bisexual), with exserted stamens. Agrimonia (agrimony) has a long spike of small honey less flowers with yellow petals; in the fruit the torus becomes hard and crowned by hooked bristles which ensure the distribution of the enclosed achenes.
Suborder IV. Neuradoideae contains only two genera of desert inhabiting herbs with yellow flowers ; and the five to ten carpels are united together and with the base of the cup-shaped torus, which enlarges to form a dry covering round the one-seeded fruits.
Suborder V. Prunoideae is characterized by a free solitary carpel with a terminal style and two pendulous ovules, and the fruit a one-seeded drupe. The torus forms a cup from the edge of which
spring the others parts of the flower. The plants are deciduous or evergreen trees or shrubs with simple leaves often with small caducous stipules, and racemes or umbels of generally showy, white or pink flowers. There are five genera, the chief of which is Prunus, to which belong the plum (Prunus communis), with sev eral well-marked subspecies—P. spinosa (sloe or blackthorn), P. insititia (bullace), P. dornestica (wild plum), the almond (P. Amygdalus) with the nearly allied peach (P. persica), cherry (P. Cerasus), birdcherry (P. Padus) and cherry laurel (P. Laurocer asus). The tribe is distributed through the north temperate zone, passing into the tropics.
Suborder VI. Chrysobalanoideae resembles the last in having a single free carpel and the fruit a drupe, but differs in having the style basal, not terminal, and the ovules ascending, not pendulous ; the flowers are also frequently zygomorphic. The genera are tropical evergreen trees or shrubs, the great majority being South American.
In North America the family is represented by about 4o genera, the largest being Crataegus (hawthorn) with about 7o species, Rubus (bramble) with 4o species, Potentilla (cinquefoil, five-finger) with about 4o species, Prunus (plum, cherry, etc.) with 20 species, and Rosa with 15 species. Potentilla is the most gen erally distributed genus in the United States.