ROSACEAE, in botany, a large cosmopolitan family of seed bearing plants which belong to the series Rosales of dicoty ledons and containing about roo genera with 2,000 species. The plants vary widely in manner of growth. Many are herbaceous, growing erect, as Geum, or with slender creeping stem, as in species of Potentilla, sometimes sending out long runners, as in straw berry; others are shrubby, as raspberry, often associated with a scrambling habit, as in the bram bles and roses, while apple, cherry, pear, plum and other British fruit trees represent the arborescent habit. Vegetative propagation takes place by means of runners, which root at the apex and form a new plant, as in strawberry; by suckers springing from the base of the shoot and rising to form new leafy shoots after run ning for some distance beneath the soil, as in raspberry; or by shoots produced from the roots, as in cherry or plum. The scram bling of the brambles and roses is effected by means of prickles on the branches and leaf-stalks.
The leaves, which are arranged alternately, are simple, as in apple, cherry, etc., but more often compound, with leaflets pal mately arranged, as in strawberry and species of Potentilla, or pinnately arranged, as in the brambles, roses, mountain ash, etc. A difference in this respect often occurs in one and the same genus, as in Pyrus, where apple (P. Malus), and pear (P. communis) have simple leaves, whereas mountain ash or rowan (P. aucuparia) has pinnately compound leaves. In warm climates the leaves are often leathery and evergreen. The leaves are stipulate, the stipules being sometimes small and short-lived, as in Pyrus and Prunus (cherry, plum, etc.), or more important structures adnate to the base of the leaf-stalk, as in roses, brambles, etc. The flowers, which are regular, generally bisexual, and often showy, are some times borne singly, as in some species of rose, or of the cloud berry (Rubus chamaemorus), or few or more together in a corym bose manner, as in some roses, hawthorne and others. The inflo rescence in agrimony is a raceme, in Poterium a dense-flowered spike, in Spiraea, a number of cymes arranged in a corymb. The parts of the flowers are arranged on a pentainerous plan, with generally considerable increase in the number of stamens and carpels. The shape of the thala mus or floral receptacle, and the relative position and number of the stamens and carpels and the character of the fruit, vary widely and form distinguishing fea tures of the different sub orders, six of which may be recognized.
Suborder I. Spiraeoideae is characterized by a flat or slightly concave receptacle on which the carpels, frequently two to five in number, form a central whorl; each ovary contains several ovules, and the fruit is a follicle except in Holodiscus. The plants are gen
erally shrubs with simple or compound leaves and racemes or pan icles of numerous small white, rose or purple flowers. This sub order is nearly allied to the family Saxifragaceae, chiefly north temperate in distribution. The largest is Spiraea, numerous species of which are cultivated in gardens; S. salicifolia occurs in Britain apparently wild in plantations, but is not indigenous. The native British meadow-sweet is S. Ulmaria; dropwort is S. Filipendula.
Suborder II. Pomoideae is characterized by a deep cup-shaped receptacle with the inner wall of which the two to five carpels are united ; the carpels are also united with each other, and each con tains generally two ovules. The fruit is made up of the large fleshy receptacle surrounding the ripe ovaries, the endocarp of which is leathery or stony and contains one seed. The plants are shrubs or trees with simple or pinnately compound leaves and white or rose-coloured often showy flowers. The genera are distributed through the north temperate zone, extending southwards in the New World to the Andes of Peru and Chile. The largest genus, Pyrus, with about 65 species, includes apple (P. Malus), pear (P. communis), wild service (P. torminalis), rowan or mountain-ash (P. aucuparia) and white beam (P. Aria). Mespilus (medlar) and Cotoneaster are also included. (See separate articles for most of the above.) Suborder III. Rosoideae is characterized by the receptacle being convex and swollen, as in strawberry, or cup-shaped, as in rose, and bearing numerous carpels, each of which contains one or two ovules, while the fruit is one seeded and indehiscent. The gen era are grouped in tribes accord ing to the form of the receptacle and of the fruit. The Potentilleae bear the carpels on a large, rounded or convex outgrowth of the receptacle. In the large genus Rubus the ripe ovaries form dru pels upon the dry receptacles ; the genus is almost cosmopolitan, but the majority of species occur in the forest region of the north temperate zone and in the mountains of tropical America. R. fruticosus is blackberry, R. Idaeus, rasp berry, and R. Chamaemorus, cloudberry. In the flower of Poten tilla, Fragaria (strawberry) and a few allied genera an epicalyx is formed by stipular structures arising at the base of the sepals. The fruits consist of numerous dry achenes borne in Fragaria on the much-enlarged succulent torus, which in the other genera is dry. In Geum (avens) and Dryas (an arctic and alpine genus) the style is persistent in the fruit, forming a feathery appendage (Dryas) or a barbed awn (avens), either of which is of service in distributing the fruit. The Potentilleae are chiefly north tern perate, arctic and alpine plants.