Dipsacales

▪ plant order

Introduction

  teasel or honeysuckle order of flowering plants, containing 45 genera and about 1,100 species, which are distributed worldwide but centred mainly in the Northern Hemisphere. The order is best known for its ornamental plants, such as Lonicera (honeysuckle), Viburnum (arrowwood and guelder rose), and Scabiosa ( scabious, or pin-cushion flower).

      Typically, plants in Dipsacales have opposite, often gland-toothed leaves, flowers in cymose (flat-topped) clusters, petals fused into a corolla tube (either regular or bilaterally symmetrical), and inferior ovaries. 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). Most members of the order are shrubby, but there are a few herbaceous members as well.

      The delimitation of families in this order is disputed, varying from two (Adoxaceae and a very broadly defined Caprifoliaceae) to seven (by splitting off Dipsacaceae, Valerianaceae, Linnaeaceae, Morinaceae, and Diervillaceae from Caprifoliaceae). Dipsacales belongs to the core asterid clade (organisms with a single common ancestor), or sympetalous lineage of flowering plants, in the Asterid II group of the Angiosperm Phylogeny Group II (APG II) botanical classification system (see angiosperm).

Adoxaceae

      Adoxaceae used to include only the herbaceous genera Adoxa and Sinadoxa, but two more genera, Viburnum (175 species) and Sambucus (elderberry, 9 species), were added under APG II. These latter genera are found mostly in the northern temperate zone, but Viburnum also grows on some tropical mountains.

      Viburnum has simple leaves and flowers with three carpels (of which two abort), but the other genera have compound leaves and five carpels. The inflorescence of Adoxaceae is usually flat-topped and has numerous small flowers. The flowers have five petals (or, more rarely, four petals), are radially symmetric (with many planes of symmetry), and have lobed stigmas on a short style, a fleshy nectary atop the ovary, and fleshy fruits (a drupe). Some dogwood plants look rather similar to Viburnum, but they have four-merous flowers. Viburnum is sometimes mistaken for Hydrangea because in both genera the external flowers of the inflorescence can be sterile and enlarged. Hydrangea, however, is a member of Cornales (the dogwood order) and has distinct, unfused petals, and it has twice as many stamens as petals.

      The diversity of habitat found in Dipsacales is illustrated by the species of viburnum growing naturally in eastern North America. V. edule (red-fruited squashberry) inhabits moist woods from Labrador to Alaska, southward into Pennsylvania, Michigan, and Minnesota, and as far west as Colorado and Oregon. V. dentatum (arrowwood) thrives not only in moist woods but also in swamps. V. nudum (possum haw) is largely limited to swamps of the eastern and southern coastal plain of the United States. In contrast, V. rufidulum (southern black haw) and V. molle prefer dry, rocky woods or hills. Viburnum is also an important horticultural genus; some of its cultivated species include V. opulus (guelder rose), V. dentatum (arrowwood), and V. macrocephalum (Chinese snowball).

      Adoxa moschatellina (muskroot) is 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 cultivation is limited to rock gardens.

Caprifoliaceae and related families

 The remaining families of the order differ from Adoxaceae in having flowers that are bilaterally symmetric, with an elongate style, a generally capitate stigma, and a nectary formed by densely packed hairs along the lower inner part of the corolla tube. While they are sometimes all placed in Caprifoliaceae, since their differences are slight, under APG II the remaining species in the order are treated as belonging to segregate families. Thus, Caprifoliaceae includes 5 genera and 220 species, mostly in northern temperate areas of East Asia and eastern North America. The largest genus is Lonicera (honeysuckle), with 180 species of shrubs and woody vines. Many honeysuckle species, some of which are intensely fragrant, are cultivated, although the introduced L. japonica and several other species are serious invasive weeds in parts of the United States.

 Different honeysuckle species show marked differences in flower colour and the length of the corolla tube. This relates to a variety of different pollination mechanisms, from bees in short-flowered species to hawkmoths in some nocturnally flowering long-tubed species and even to hummingbirds in some long-tubed, red-flowered species in Mexico and the southern United States. Another widely cultivated genus of Caprifoliaceae is Symphoricarpus, with 17 mostly North America species of deciduous shrubs, including S. albus ( snowberry) and S. orbiculatus (coral berry).

Dipsacaceae

 Dipsacaceae, or the teasel family, includes 11 genera and 290 species, most of them Eurasian or African (many are from the Mediterranean region). They are herbs with bilaterally symmetric flowers clustered in heads or involucres, a well-developed epicalyx, and fruits that are dry and single-seeded, with awns or bristles. Dipsacus sativus (teasel) is noted for its compact head of flowers in which elongate, stiff bracts (leaflike scales) accompany each flower. The ripened heads were used in Roman times to raise the nap of woolen cloth, a process known as fulling (felting) (see felting). (The use of fuller's teasel has since been replaced by mechanical methods.)

      Another important genus of Dipsacaceae is Scabiosa (scabious), the pin-cushion flower genus with 80 species, of which at least 20 species are ornamentals. Cephalaria has 65 species, including cornfield weeds such as C. syriaca and the ornamental C. transylvanica, a tall annual that produces large, stiff, globe-shaped, white to bluish flower heads and has divided leaves. Knautia has 60 species, some cultivated, such as K. arvensis (field scabious). Succisa pratensis (devil's bit scabious), a blue-flowered perennial, grows wild in European meadows. Its leaves are entire or slightly lobed and oval to narrow in shape.

Valerianaceae

      Valerianaceae, or the valerian family, contains 17 genera and 315 species, most of them in the genera Valeriana (200 species) and Valerianella (80 species). Members of this family are characterized by the rank odour of their stems and leaves when dried; they are herbs or small shrubs with small regular to monosymmetric flowers, usually with a spur. They are distributed in the Northern Hemisphere and in Andean South America. Valeriana officinalis (garden heliotrope (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. Nardostachys grandiflora ( spikenard) is a perennial herb of the Himalayas that produces an essential oil in its woody rhizomes.

Linnaeaceae

 Linnaeaceae includes 4 or 5 genera and 36 species of shrubs and herbs native to the temperate regions of Southeast Asia and North America (extending into Mexico). The best-known member of the family is Linnaea borealis ( twinflower), a trailing evergreen that is circumpolar in distribution in high northern latitudes. It also includes Abelia, a genus of 30 species native to East Asia and Mexico, with many cultivated varieties. Members of this family have more irregular flowers than Diervillaceae.

Morinaceae

      Morinaceae contains 3 genera (Acanthocalyx, Cryptothladia, and Morina) with 13 species native to Eurasia, from the Balkans to China. They are robust perennial herbs with leaves joined at the base and flower clusters in successive whorls (verticillasters or heads). Flowers are bilaterally symmetric and subtended by an extra whorl called the epicalyx. In the Balkans the seeds of Morina persica are eaten like rice.

Diervillaceae

      Diervillaceae contains 2 genera, Diervilla, with 3 North American species, and Weigelia, with 10 East Asian species. Many of these are cultivated as ornamental shrubs in temperate areas for their colourful flowers.

Paul E. Berry

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