Cornales

▪ plant order

Introduction

  dogwood order of flowering plants, comprising 7 families and almost 600 species. The main families are Cornaceae, Hydrangeaceae, and Loasaceae. The other families are Nyssaceae, which is sometimes included in Cornaceae, and the smaller single-genus families Curtisiaceae, Grubbiaceae, and Hydrostachyaceae. These are mostly woody plants; their flowers usually have parts in multiples of four; and the petals, when present, are usually not joined. The ovary is inferior and contains several carpels, and the fruits are fleshy with stony seeds.

      Cornales is the basalmost order of 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).

Cornaceae

 Cornaceae, or the dogwood family, is the largest family in the order, though it has just two genera: Cornus (65 species) and Alangium (20 species). Cornus is noted for its woody ornamental species that are native to both coasts of North America and to East Asia. Some members, such as Cornus florida (flowering dogwood), are chiefly ornamental, whereas the European Cornus mas (cornelian cherry) has edible fruit, and Cornus macrophylla yields wood for furniture. In the flowering dogwoods the flowers are small, and the conspicuously expanded structures are coloured bracts (specialized leaves) that surround the cluster of true flowers.

Hydrangeaceae

 Members of Hydrangeaceae, or the hydrangea family, are usually rather robust herbs or shrubs, with opposite leaves and a line running across the stem between opposing leaf stalks. The family includes 17 genera and 190 species, most of them in warmer temperate zones, though a few species enter the tropics. The flowers have free petals that are valvate in bud, there are at least twice as many stamens as petals, and the ovary is half to fully inferior. Hydrangeas (hydrangea) (Hydrangea) are known to most gardeners as shrubs, although some are woody vines or small trees. In the early spring the common hydrangea, or Hortensia (H. macrophylla), popular with horticulturists, is sold as a potted plant in cool areas. Hydrangea flowers are produced in large, showy white, blue, or pink clusters. In some species flower colour seems to be related to soil acidity. The pink-flowered hortensias, for example, show a tendency to turn blue when iron filings or alum are added to the soil to increase acidity. In a number of hydrangea species, the sepals of the marginal flowers of the flower cluster are enlarged and look like petals. Two other members of the hydrangea family often grown in gardens are Philadelphus, known as mock orange (Philadelphus) or sweet syringa, and Deutzia. These shrubs and their many cultivated varieties are widely planted in shrub borders for the white flowers that appear in late spring.

Loasaceae

      Members of Loasaceae, or the stickleaf family, are typically coarse herbs or shrubs, often with stinging hairs. The flowers, with separate, spreading petals, numerous radiating stamens with long filaments, and inferior ovary, are distinctive. The family has 14 genera and 265 species, most of them North American, but there are also species known from South America, Africa, and the Marquesas Islands in the Pacific. The main genera are Loasa (105 species), Caiophora (65 species), and Mentzelia (60 species).

Nyssaceae

 Nyssaceae, or the tupelo family, contains 5 genera and 22 species, including Nyssa (tupelo), which produces good timber for underwater use, and Davidia involucrata ( dove tree; the name derives from its two big, white, leafy bracts that subtend the flowers).

Other families

      Among the smaller families in Cornales is Hydrostachyaceae (sometimes included in Hydrangeaceae), a single genus (Hydrostachys) with 20 species of aquatic herbs native to central and southern Africa and Madagascar. The rosette-forming leaves can be highly divided and usually have small, scaly or fringed appendages. Flowers are very reduced and unisexual, tightly arranged along a spike; the male flowers have a single anther, and the female flowers have two elongate styles and form a capsule with many tiny seeds. Two last families in the order are Grubbiaceae and Curtisiaceae, which are sometimes joined into a single family and each of which comprises a single genera of trees. Grubbia, with three species in the Cape Province of South Africa, are heathlike shrubs with opposite leaves and conelike clusters of small flowers. Curtisia has two species of southern African trees that are useful as a timber source (assagai wood) for furniture and other small construction.

Paul E. Berry

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