rose family

Rosaceae Fossil range: 110 Ma PreЄ Є O S D C P T J K Pg N ↓ Cretaceous - Recent
Flower of Crataegus oxycantha
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Rosales Family: Rosaceae Juss.
Global distribution of Rosaceae

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).

Distribution

The Rosaceae have a worldwide range, but are most diverse in the northern hemisphere.

Taxonomy

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

Diversity

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.

Description

The Rosaceae can be herbs, shrubs, or trees.

The leaves are generally arranged spirally. They can be simple, as in the most primitive species, or pinnately compound (both odd or even). 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 caracteristic cup-like structure called hypanthium. They can be arranged in racemes, spikes, 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 false fruits, like the pome (e. g. in Malus, the apple), or the cynorrhodon (rose-hip). Many fruits of the family are edible.

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 four genera 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.

Economic importance

The rose family is probably the third most economically important^{[citation needed]} 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.

External links

• Genome Database for Rosaceae at Washington State University
• Rosaceae at the University of Illinois.
• Rosaceae full family list at Plants For A Future - Species Database.
• Family Rosaceae Flowers in Israel
• Rosaceae of Chile, by Chileflora
• Family Rosaceae Diagnostic photos of many different species at the Morton Arboretum
• Rosaceae at the Encyclopedia of Life