ROSALES

rose order of dicotyledonous flowering plants, a division of the subclass Rosidae. Its members include some of the best-known ornamental and edible-fruit plants in the temperate parts of the world. Among them are the roses, hydrangeas, spireas, hawthorns, apples, peaches, cherries, pears, plums, strawberries, raspberries, currants, and gooseberries. The classification of the Rosales followed here comprises 24 families totaling approximately 320 genera and 6,700 species. The sizes of the families vary greatly. Three of them are monotypicthat is, they have only one speciesand nearly half of the families have 10 or fewer species. At the other extreme, the rose family (Rosaceae) includes about 45 percent of the species in the order, the three largest families contain two-thirds of the species, and the largest seven families comprise more than 90 percent of the members of the order. the rose order of flowering plants, belonging to the class known as dicotyledon (characterized by two seed leaves). The order consists of about 320 genera and 6,700 species classified into 24 families. Its members include some of the best-known ornamental and edible-fruit plants in the temperate parts of the world. Among them are the roses, hydrangeas, spireas, hawthorns, apples, peaches, cherries, pears, plums, strawberries, raspberries, currants, and gooseberries. The rose family (Rosaceae) includes about 45 percent of all the species in the order. The other important families include Saxifragaceae, Hydrangeaceae, Grossulariaceae, and Crassulaceae. Many of the remaining families have 10 or fewer species each. Most species in the Rosales occur in north temperate regions of the Old and the New World, and they are particularly abundant in East Asia, Europe, and North America. The Rosales is an extremely diverse order, with members ranging from small herbs to shrubs and woody climbers to small and large trees. Habitats range from sea level to alpine meadows, and many species are found in association with human activities. The cultivated fruit trees of the family Rosaceae thrive best in well-drained soil, and commercial orchards are frequently in hilly or rolling countryside. The Rosaceae has about 3,000 species of small and medium-sized trees, shrubs, and perennial herbs, with woody plants predominating. Roses (genus Rosa) are probably the most widely recognized and universally favoured of ornamental flowering plants. Hundreds of varieties are cultivated in all types of settings, and many hybrids have been produced by crossbreeding. Spirea (Spiraea) and cinquefoils (Potentilla) are also popular garden plants. Hawthorn (Crataegus), mountain ash (Sorbus), and flowering cherry (Prunus) are grown as ornamental trees. The most important fruits of the Rosales order are also members of the rose family. Apples (Malus) and peaches (Prunus) form an economic base for several regions around the world. Other members of the group are strawberries (Fragaria); pears (Pyrus); cherries, plums, apricots, and almonds (Prunus); quinces (Cydonia); and blackberries and raspberries (Rubus). The wood of the black cherry (Prunus serotina) and the European wild cherry (Prunus avium) is used to make high-quality furniture, and pearwood is also highly valued. Plants of a number of species of the rose family contain dangerous cyanide compounds. Peach pits, bitter almonds, and several kinds of wild cherry are poisonous to animals and humans. The foliage of chokecherry (Prunus virginiana), wild black cherry (P. serotina), and species of mountain mahogany (Cercocarpus) are sometimes fatal to browsing animals. Members of the saxifrage family (Saxifragaceae) commonly occur in mountainous and arctic regions and are notable for their ability to grow and thrive on exposed rocky crags and rock fissures. Plants in the stonecrop family (Crassulaceae) are concentrated in southern Africa, southern Asia, and the Mediterranean and show adaptations to survival in dry climates; some species are grown as potted plants and in rock and succulent gardens. Currants and gooseberries are produced by shrubs of the genus Ribes, belonging to the currant family (Grossulariaceae). Hydrangeas (Hydrangea), of the family Hydrangeaceae, range in size from shrubs to small trees and produce the popular flowers of that name. Seven families of the Rosales order are mostly confined to the temperate and subtropical climates of the Southern Hemisphere. Of these, the Cunoniaceae is a family of trees and shrubs found especially in Australia and New Guinea, and extending into South America. The much smaller coco plum family (Chrysobalanaceae) ranges through the tropics, chiefly in the Amazon region of South America. The order Rosales includes a vast range of forms, from small creeping herbs to giant hardwood trees. Many members, particularly in the Rosaceae, have thorns or prickles. Simple leaves are common in the order, but several of the smaller families have compound leaves. The Rosaceae show the greatest variety of leaf types, ranging from simple and lobed types to pinnately compound ones. Most Rosaceae have alternate leaves, but members of other families may have opposite ones. Leaves typically have stipules (small leaflike appendages). Flowers in the Rosales are usually rather flat or shallowly cup-shaped. They are often showy, and usually have four or five petals and sepals arranged in radial symmetry and joined to form a floral cup. The flowers are bisexual (having both female and male reproductive structures), and pollen-bearing stamens are abundant. Fruits may be dry or fleshy; some contain stony pits. Seeds have small embryos and no endosperm (food-storage tissue). In members of the Rosales order, colour and scent draw insect pollinators to the flowers to feed on the copious pollen and spread it to receptive female organs of other plants. Seed dispersal depends on the type of fruits produced. Species with fleshy edible fruits attract birds and other animals that disperse seeds by ingesting and later excreting them. Among some families, tiny, light seeds or large, winged seeds are spread by the wind. Other groups produce seeds or fruits with hooks or barbs that catch on animal fur or human clothing and are carried from place to place. Reproduction does not always depend on seeds, however; strawberries and raspberries reproduce asexually by vegetative propagation while retaining the ability to form seeds. Additional reading K.R. Robertson, The Genera of Rosaceae in the Southeastern United States, Journal of the Arnold Arboretum , 55(2):303332, 55(3):344401, and 55(4):611662 (1974).