1911 Encyclopædia Britannica/Umbelliferae

UMBELLIFERAE, in botany, an order of polypetalous Dicotyledons belonging to the series Umbelliflorae, which includes also the orders Araliaceae (ivy family) and Cornaceae (dogwood family). It contains r8o genera with about 1400 species, occurring in all parts of the world but chiefly in north temperate regions. It is well represented in the British flora by 35 genera. The plants are annual or perennial herbs, rarely shrubby as sometimes in Bupleurum, with generally a very characteristic habit, namely stout erect stems with hollow internodes, alternate innately compound exstipulate sheathing leaves and compound umbels of small, generally white, flowers.

Fig. 1.—Perfoliate leaf of a species of hare's-ear (Bupleurum rotundifolium). The two lobes at the base of the leaf are united, so that the stalk appears to come through the leaf.

An example of an annual is the common fool's parsley, Aethusa Cynapium; carrot (Daucus Carole) is a biennial; others are perennial, persisting by means of tubers or rhizomes—such are hogweed (Heracleum), Angelica, Peucedanum, and others. Some genera have a creeping stem as in Hydrocotyle (pennywort), a small herb with a creeping filiform stem and, in the British species, entire leaves. Bupleurum has simple, entire, often perfoliate leaves (fig. 1). Azorella, a large genus in south temperate regions, has a peculiar caespitose habit, forming dense cushions often several feet in diameter and persisting for many years. Eryngium, represented in Britain by sea-holly (E. maritimum), is a large genus of rigid often glaucous herbs with spiny-toothed leaves, which in some South American species with narrow parallel-veined blade and broadly sheathing base recall those of a Monocotyledon such as Agave or Bromelia. In sanicle (Sanicula), Astrantia and others the leaves are palmately divided; and there is a great variety in the degree of division in the characteristic pinnate leaf, which varies from simply pinnate to a branching of the blade to the fifth or sixth order.

Fig. 2.—Diagram of flower of Umbelliferae.

There is also considerable variety in the development of the umbel, which is usually compound but sometimes simple, as generally in Hydrocotyle and Astrantia, rarely reduced to a single flower as in species of Hydrocotyle. In Eryngium the flowers are crowded into dense heads subtended by a whorl of rigid bracts. A terminal flower is sometimes present as in carrot, where it is distinguished by its form and dark colour. The presence or absence of bracts and their form when present afford useful diagnostic characters. When present at the base of the primary rays of the umbel they form the involucre, and the involucel when at the base of a partial umbel. In Astrantia the simple umbel is enveloped by a large, often coloured, involucre.

(From Vines's Student's Text Book of Botany, by permission of Swan, Sonnenschein & Co.)

Fig. 3.—A, Pistil; B, Fruit of the Caraway (Carum Carui); enlarged.

d, epigynous disk; f, ovary; n, stigma; p, pedicel. In B the two carpels have separated so as to form two mericarps (m). Part of the septum constitutes the carpophore (a).

The small epigynous flowers are usually hermaphrodite and regular, with parts in fives. The sepals are usually very small, often represented only by teeth on the upper edge of the ovary; the petals are usually obovate or obcordate in shape, often with the tip inflexed; the stamens have long slender filaments bent inwards in the bud but ultimately spreading; the two carpels are in the median plane; the two-celled ovary is surmounted by an epigynous glandular disk—the stylopodium—which bears the two styles. Each ovary-cell contains a single pendulous anatropous ovule with a ventral raphe and a single integument. In the development of the flower the stamens appear first, followed by the petals, the sepals and the rudiments of the carpels in succession. The flowers are rendered conspicuous by being massed into more or less dense flat-topped inflorescence's. A resemblance to the rayed heads of Compositae is suggested in the frequently larger size of the flowers on the circumference of the umbel which are often sterile and zygomorphic from the larger size of the outer petals. This arrangement allows a large number of flowers to be visited in a short time. The flowers are generally white, sometimes pink or yellow, very rarely blue; they are generally scented, but the whole plant has an odour from the general presence in the tissues of an ethereal oil or resin. The flower is widely open, the petals and stamens radiating from the central disk (fig. 3, d), on which honey is secreted, and is thus accessible to quite short-lipped flies. Cross-pollination is rendered necessary by the flowers being generally markedly proterandrous; the stamens throughout the umbel have generally shed their pollen before the stigmas have begun to be functional even in the outer flowers.

The fruit is again very characteristic; a schizocarp which splits down the septum to form two dry one-seeded mericarps which are at first attached to, or pendulous from, an entire or split central axis or carpophore (fig. 3). The form of the mericarp affords valuable characters for distinguishing genera. On the outer surface of each are generally 5 ridges (primary ridges), between which are sometimes 4 secondary ridges; oil-cavities, vittae, are often present in the intervening furrows. The fruits are variously adapted for distribution; they are sometimes thin and flat as in Hemcleum, when they are easily carried by the wind, or, as in carrot, provided with hooks. The seed contains a small embryo embedded in oily endosperm, which is usually cartilaginous in texture.

Fig. 4.—Water Dropwort, Oenanthe crocata, with thickened root fibres, about half nat. size.

1, Flower; 2 and 3, Side and front view of fruit; enlarged.

The order is divided into 9 tribes depending on the form of the fruit, whether compressed, angled, grooved, constricted, &c., and the presence or absence of vittae. The 35 British genera include representatives of 7 of the tribes. The following may be mentioned: Hydrocotyle (pennywort), Eryngium (sea-holly), Sanicula (sanicle), Conium (hemlock, q.v.), Smyrnium (Alexanders), Bupleurum (hare's-ear), Apium (celery, q.v.), Carum (caraway, q.v.), Conopodium or Bunium (earth-nut, q.v.), Myrrhis (Cicely), Chaerophyllum (chervil), Foeniculum (fennel, q.v.), Crithmum (samphire), Oenanthe (water dropwort), Aethusa (fool's parsley, q.v.), Angelica (q.v.), Peucedanum (hog's fennel, parsnip, q.v.), Heracleum (hogweed), Daucus (carrot). Petroselinum sativum is common parsley (q.v.).