Rosaceae

Rosaceae, or the rose family is a large family within the Rosales order of flowering plant, that comprises of about 2830 species in 95 genera. The name is derived from the rose genus, Rosa, which is the type genus. The largest genera out of this family (not including cultivars) are Alchemilla, Sorbus, Crataegus, Cotoneaster, and Prunus.

Roses can be herbs, shrubs, or trees, but most are deciduous, leaving some evergreen. They are found worldwide, but are mostly diverse in the Northern Hemisphere (see distribution).

Several important economic products come from this family, which include fruits like apples, cherries, peaches, pears, raspberries, strawberries and almonds. They are also used for ornamental purposes. Some of these include roses, meadowsweets, photinias, firethorns, rowans, and hawthorns.

Distribution
Members of the family are found nearly everwhere but Antarctica. Most of these members are endemic to the Northern Hemisphere than anywhere else on the world.

Taxonomy
The family was originally divided into four subfamilies, Rosoideae, Spiraeoideae, Maloideae, and Amygdaloideae. Recent work has proven that not all these groups were monophyletic. Now Rosaceae is broken into 3 subfamilies (one still being Rosoideae). A cladogram according to the APG II system is shown below:

Though the boundaries of Rosaceae haven't yet been disputed, there is an agreement on how many genera it should be divided into. Areas of divergent include the genus, Potentilla, and Sorbus. Compounding this problem is that apomixis is common in several genera. This creates an uncertainty in the number of species in each genera. For example, Cotoneaster has between 70 and 300 species, Rosa around 100, Sorbus 100 to 200, Crataegus 200 to 1,000, Alchemilla around 300, Potentilla about 500, and Rubus, possibly hundreds or thousands of species.

Leaves
The leaves are usually arranged in a spiral, but some species have opposite arrangement. Leaves can be either alternate or pinnately-compound. There are about 30 genera with compound leaves. The margin of the leaves is serrated. Stipules are common. Two glands are usually showing on the end of the petiole.

Flowers
The flowers are usually showy. They are radially symmetrical, and usually hermaphroditic. The flowers usually have 5 sepals, 5 petals, and several stamens. The bases of the sepals, petals, and stamen form a cup-like structure known as a hypanthium. They can be arranged in racemes, spikes, or heads.

Fruits and seeds
The fruits come in several shapes and sizes, and were once main characteristics of classifying Rosaceae into subfamilies. They can be follicles, capsules, nuts, achenes, drupes, and accessory fruits. Many of these fruits are edible.

Genera
For a complete list, see List of Rosaceae genera


 * Rosoideae: Traditionally composed of genera with aggregate fruits that are made of achenes or drupelets, or often the fleshy part of the fruit are the receptacle, or stalk holding carpels. The circumscription is now narrowed, but it is still a diverse group with 5 or 6 tribes, and atleast 20 genera. Examples include roses, blackberries, raspberries, strawberries, Potentilla, and Geum.


 * Spiraeoideae: Traditionally composed of genera of non-fleshy fruits consistant of 5 capsules. It is sometimes restricted to Spiraea and Sorbaria, and respective allies, or expanded to include Maloideae or Prunoideae.


 * Maloideae: Traditionally composed of genera with fruits consisting of five capsules (cores) in a fleshy or stony endocarp, surrounded by a mesocarp and hypanthium tissue. These fruits are known as pomes. The woody genera, Lindleya and Vauquelinia share a haploid chromosome count of 17, with pomiferous genera Kageneckia and Gillenia. Recent evidence shows that Prunoideae may have evolved from an expanded Spiraeoideae. Examples include apples, Cotoneaster, and hawthorn.


 * Prunoideae: Traditionally composed of genera with one drupe with a seam, two veins next to the seam, and one opposite the seam. This subfamily was completely comprised of Prunus, but Maddenia, Oemleria, and Prinsepia were added some time later. Examples include plums, peaches, almonds, cherries, and apricots.


 * Dryadoideae: Traditionally composed of genera with achenes with hairy styles, most of which have root nodules which host bacteria. Examples include Dryas, Cercocarpus, Chamaebatia, Cowania and Purshia.

Importance to economy
Rosaceae is one of the most economically important family of crops, including apples, pears, quinces, medlars, loquats, almonds, peaches, apricots, plums, cherries, strawberries, raspberries, blackberries, boysenberries, loganberries, prunes, sloes, and cut roses.

Many genera are also used as ornamental plants. These include Cotoneaster, Crataegus, Kerria, Photinia, Potentilla, Prunus, Pyracanta, Rhodotyphos, Rosa, Sorbus, Spiraea and several others.

Though several members of Rosaceae are beneficial to human use, some are weeds in part of the world, costing money to be controlled. These invasive plants can create negative impacts on their new environment. Some of these include members of the Acaena, Cotoneaster, Crataegus, Pyracantha, and Rosa genera.