The Rosaceae or rose family is a large family of plants, with about 3,000-4,000 species in 100-120 genera. Traditionally it has been divided into 4 subfamilies (Rosoideae, Spiraeoideae, Maloideae or Pomoideae, and Amygdaloideae or Prunoideae), primarily diagnosed by the structure of the fruits, but this has not been universally followed. Recent work has identified that the traditional four subfamilies are not all monophyletic, but the structure of the family is still awaiting complete resolution. Identified clades include:
Subfamily Rosoideae: Traditionally composed of those genera bearing small fruits, each of which is an achene or drupelet, and often the fleshy part of the fruit (e.g. strawberry) is the hypanthium or the stalk bearing the carpels. The circumscription is now narrowed (excluding, for example, the tribe Dryadeae), but it still remains a diverse group containing 5 or 6 tribes and 20 or more genera. Rose, blackberry, raspberry, strawberry, Potentilla, Geum.
Subfamily Spiraeoideae: Traditionally those genera which bear non-fleshy fruits consisting of five capsules. Now perhaps to be restricted to Spiraea and Sorbaria and their respective allies.
Subfamily Maloideae: Traditionally this includes the genera (apple, cotoneaster, hawthorn, pear, quince, rowan, whitebeam, etc), whose fruits consist of five capsules (called "cores") in a fleshy endocarp, surrounded by the ripened stem tissue. This structure is called a pome (after the French name for an apple, pomme). To these are added the woody genera Lindleya and Vauquelinia, which share a haploidchromosome count of 17 (x=17) with the pomiferous genera, Kageneckia, in which x=15, and the herbaceous genus Gillenia (x=9), which is the sibling to the remaining maloids.
The rose is a rose and was always a rose; But the theory now goes That the apple's a rose, And the pear is, and so's The plum, I suppose. The dear only knows What will next prove a rose. You, my love, are a rose, but were always a rose.
