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The Rosaceae or rose family is a large family of plants, with about 3000 species in 100 genera (according to the Kew Royal Botanical Gardens). The name is derived from the genus Rosa. The largest genera are Sorbus, Crataegus and Cotoneaster (more or less 260 species each).
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The Rosaceae have a worldwide range, but are most diverse in the northern hemisphere.
The family was traditionally divided into four subfamilies: Rosoideae, Spiraeoideae, Maloideae, and Amygdaloideae, primarily diagnosed by the structure of the fruits. More recent work has identified that not all of these groups were monophyletic. A more modern view comprises three subfamilies, one of which (Rosoideae) has largely remained the same. A cladogram of the family according to APG II is shown below
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While the boundaries of Rosaceae are not disputed, there is not general agreement as to how many genera it should be divided into. Areas of divergent opinion include the treatment of Potentilla s.l. and Sorbus s.l..
Apomixis is common in several genera, including Cotoneaster, Crataegus, Rubus and Sorbus. This results in an uncertainty in the number of species in the family, due to the difficulty of dividing apomictic complexes into species. Cotoneaster contains between 70 and 300 species, Crataegus between 200 and 1,000, Rubus hundreds, or possibly thousands, of species, and Sorbus 100 to 200 species. Alchemilla contains around 300, Potentilla around 500 species, and Rosa around 100, including the taxonomically complex dog roses.
The Rosaceae can be herbs, shrubs, or trees.
The leaves are generally arranged spirally, but have an opposite arrangement in some species. They can be simple or pinnately compound (either odd- or even-pinnate). Compound leaves appear in around 30 genera. The leaf margin is most often serrate. Stipules are generally present and are a primitive feature within the family, independently lost in many groups of Spiraeoideae. Two glands are generally present on the apical end of the petiole.
The flowers are generally showy. They are actinomorphic (i.e. radially symmetrical) and almost always hermaphroditic. Rosaceae generally have five sepals, five petals and many spirally arranged stamens. The bases of the sepals, petals, and stamens are fused together to form a characteristic cup-like structure called hypanthium. They can be arranged in racemes, spikes, or heads, solitary flowers are rare.
The fruits come in many varieties and were once considered the main characters for the definition of subfamilies amongst the Rosaceae, giving rise to a fundamentally artificial subdivision. They can be follicles, capsules, nuts, achenes, drupes (Prunus) and accessory fruits, like the pome of an apple, or the hip of a rose. Many fruits of the family are edible.
Identified clades include:
The rose family is probably the third most economically important crop plant family (after the grass family and the pea family), including apples, pears, quinces, medlars, loquats, almonds, peaches, apricots, plums, cherries, strawberries, raspberries, blackberries and cut roses among the crop plants belonging to the family.