Aster is an important genus of the Asteraceae family that accounts for approximately 200 flowering plants, most of which are native to Eurasia. Asters are highly prized by gardeners and the cut flower industry for their colorful, daisy-like flowers. Until the 1990s, the Aster genus consisted of three times as many species as it does today. Former asters that are native to North America are now listed under 10 different separate genera. These North American genera are still informally referred to as asters by horticulturalists.
The flowering plant A. amellus is the official type species of the Aster genus. A type species is a single species that has all of the characteristics that are associated with a particular category of botanical nomenclature. A. amellus is known informally by the common names fall aster, Italian aster and Michaelmas daisy. This perennial plant provides bunches of small flowers during the autumn that consist of purple to lavender petals with a bright yellow center.
Alpine Aster (A. alpinus) is a notable species of Aster in that it is the only true member of this genus that is native to North America. The perennial herb reaches a height of 6 to 12 inches (about 15 to 30 centimeters) when it is mature and produces annual flowers in the late spring. Most cultivars of this species have pink or purple blooms and thrive in rocky, well-drained areas that offer abundant sun.
Apple blossom (A. novi-belgii) is another member of this species that is popular amongst gardeners. This hardy perennial grows considerably faster than most members of this genus and can rapidly spread to take over a modest-sized area of a flower garden. Apple blossoms provide dense, lance-shaped foliage throughout the growing season and light pink blooms during the early fall. These plants perform well in a mixed flower garden and can be divided after one year of growth.
Most members of the Aster genus are adaptable plants that are capable of living in a wide range of climates including hardiness zones four through nine. Asters are easiest to propagate by dividing, but new plants can also be grown from seed and root cuttings. Most asters prefer either full sun or partial shade and thrive in soil that has been properly fertilized. Asters should be watered frequently during the heat of the summer in order to ensure plenty of healthy flowers. Many popular asters are susceptible to mildew infestations that can be treated with soapy water or commercial sprays.