The Rosaceae or rose family is a large family of plants, with about 3,000-4,000 species in 100-160 genera. Traditionally it has been divided into four subfamilies: Rosoideae, Spiraeoideae, Maloideae, and Amygdaloideae. These subfamilies are primarily diagnosed by the structure of the fruits, although this approach is not followed universally. Recent work has identified that the traditional four subfamilies are not all monophyletic, but the structure of the family is still awaiting complete resolution.
Genera
See List of Rosaceae genera.
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 (or Pomoideae): Traditionally this includes those genera (apple, cotoneaster, hawthorn, pear, quince, rowan, whitebeam, loquat, etc), whose fruits consist of five capsules (called "cores") in a fleshy endocarp, surrounded by the ripened stem tissue. This fruit is called a pome. To these are added the woody genera Lindleya and Vauquelinia, which share a haploid chromosome 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.
- Subfamily Amygdaloideae (or Prunoideae): Traditionally those genera whose fruits consist of a single drupe with a seam, two veins next to the seam, and one vein opposite the seam. Now extended to include the five genera Exochorda, Maddenia, Oemleria, Prinsepia and Prunus (plum, peach, almond, cherry, apricot).
- Tribe Dryadeae: Fruits are achene with hairy styles. Includes five genera (Dryas, Cercocarpus, Chamaebatia, Cowania and Purshia), most species of which form root nodules which host the nitrogen-fixing bacterium Frankia.
- Tribe Neillieae: Neillia (including Stephanandra) and Physocarpus.
Amongst these groups, Neillieae appears to be the sister group to Maloideae, and Dryadeae may be a sibling group to Rosoideae. Other genera, for example Kerria, appear not to belong to any of these groups.
Fruits
The fruits of the Rosaceae come in varieties. The most common is a drupe but there are many others. Apples, pears, quinces, and most other members of the Maloideae are pomes, but some are capsules such as in Lindleya. The fruit of a strawberry is an achene held by a red pseudocarp. Pomes and pseudocarps are false fruits, while drupes are true fruits. Most fruits of the family are edible and are very important in flavoring such as strawberries, cherries and apples. Almonds are raised for their stones which are used as smoked or salted nuts. Apples and strawberries are hybrids of different species in the same genus.
Economic importance
The rose family is probably the third most economically important crop plant family (after the grass family and the pea family), with apples, almonds, strawberries and cut roses among its members.
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