DIPSACALES

the teasel order of flowering plants, belonging to the class known as dicotyledon (q.v.; characterized by two seed leaves). It comprises 40 genera and about 1,100 species in four families and is distributed throughout the world, but is centred mainly in the Northern Hemisphere. The order is best known for its ornamental plants, such as the honeysuckle, the arrowwood, the wayfaring tree, the guelder rose, and the scabious. The diversity of habitat found in Dipsacales is illustrated by the species of Viburnum (Caprifoliaceae family) growing naturally in eastern North America. V. edule, the red-fruited squashberry, inhabits moist woods from Labrador to Alaska, southward into Pennsylvania, Michigan, and Minnesota, and as far west as Colorado and Oregon. A variety of arrowwood, V. dentatum, thrives not only in moist woods but also in swamps. Possum haw (V. nudum) is largely limited to swamps of the eastern and southern coastal plain. In contrast, V. rufidulum (southern black haw) and V. molle prefer dry, rocky woods or hills. Thirteen of the 18 genera of the honeysuckle family (Caprifoliaceae) are under cultivation. Many genera consist of relatively few species. Viburnum, however, has about 225 species, including the guelder rose (V. opulus variety opulus), the arrowwood (V. dentatum), and the Chinese snowball (V. macrocephalum variety sterile). Other significant genera of the Caprifoliaceae are Lonicera, Sambucus (elderberry), Symphoricarpos, and Weigelia. The valerian family (Valerianaceae) comprises 10 genera and 400 species of herbs distributed chiefly in the Northern Hemisphere. Its members are characterized by the rank odour of their stems and leaves when dried. Valeriana officinalis, the garden heliotrope, is a perennial herb prized for its spicy, fragrant flowers; it is native in Europe and western Asia. Its dried rhizome yields valerian, a natural sedative. Another member of the Valerianaceae, the spikenard (Nardostachys jatamansi), is a perennial herb of the Himalayas and produces an essential oil in its woody rhizomes. The Dipsacaceae is a natural family comprising herbs placed in 8 to 12 genera and 300 species. Dipsacus sativus is noted for its compact head of flowers in which elongate, stiff bracts (leaflike scales) accompany each flower. The ripened heads were used even in Roman times to raise the nap of woolen cloth, a process known as fulling. (Fuller's teasel has since been replaced by mechanical methods.) Another important genus of Dipsacaceae is Scabiosa, the pin-cushion flower genus, 21 species of which are ornamentals. Many other members of the family are cultivated as ornamentals. Himalayan whorlflower (Morina longifolia), sometimes placed in a family of its own, has thistlelike leaves and produces spikes of tubular flowers about 90 cm (3 feet) tall that open white and turn scarlet. Pterocephalus parnassi, from mountains of southeastern Europe, is a low, perennial plant with purplish flowers. Cephalaria transylvanica, a tall annual, produces large, stiff, globe-shaped, white to bluish flower heads and has divided leaves. Devil's bit scabious (Succisa pratensis), a blue-flowered perennial, grows wild in European meadows. Its leaves are entire or slightly lobed and oval to narrow in shape. The fourth family, Adoxaceae, consists of Adoxa moschatellina, the muskroot, widely distributed in northern regions. It is a low-growing, perennial herb composed of a basal cluster of leaves and a single stem. It has a musky odour (as its name implies), and its use is limited to rock gardens. The American elderberry and the bush honeysuckle produce rhizomes that send up new shoots to propagate the species vegetatively. Such plants often form dense colonies. Seeds, however, are produced in abundance by all members of the Dipsacales growing naturally. Inflorescences in this order range from paired flowers in the twinflower (Linnaea) to the showy, compactly branched, flat-topped inflorescences (cymes) produced by the American elderberry. Several other types of inflorescences are produced in certain species. A model flower of this group of plants has four to five units in each whorl of sepals, petals, and stamens (male). Sepals may be undiverged to form a funnel-shaped calyx; petals are always fused to form an often bell-shaped corolla. Stamens are attached basally to the petals. The pistil (female) is composed of two or more carpels in which the basal, swollen ovary is topped by a slender style that ends in the pollen-receptive stigma. Stigmas are the same in number as the chambers of the ovary, and each chamber produces one ovule. A distinctive feature of the teasel order is the departure of all floral parts from the top of the ovary; it is inferior in position. Pollination is generally effected by insects, but in some species of honeysuckle of the western United States, hummingbirds pollinate the flowers. Following pollination and fertilization, the ovule becomes the seed and the ovary the fruit. Several types of fruits are found in the Dipsacales. Those that mature fleshy are berries, or, if the layer next to the seed is hard, drupes. Many species produce dry fruits that either split (capsules) or remain closed (achenes). Fleshy fruits and their seeds are dispersed by birds. Some species in the teasel family produce spiny fruits or inflorescences that cling to passing animals and are scattered widely. Features shared by most families in the Dipsacales include opposite leaves, inflorescences in cymes (oldest flowers at top), united petals, anthers separate from each other, and an inferior ovary. In most genera, petals are alike in shape, but some members of the order develop two-lipped flowers in which one half of the flower is the mirror image of the other half (bilateral symmetry).