1. Cynareæ, Thistle Group. Flowers all ☿, regular, with tubular corollas. The receptacle is covered with numerous bristles, which surround the flowers without any definite order, or the edges of the grooves in which these are placed have a well-marked fringe. The involucral leaves are numerous, imbricate, and are either prolonged into a thorn or terminate with a membranous edge. The style has been described on page [568] (Fig. [609] C). Nearly all have a hairy or feathery pappus. The filaments are sensitive.
Carduus (Thistle); capitula ovoid; involucral leaves compact, imbricate, with thorny points; the pappus-rays are hair-like and united at the base by a ring (i.e. the calyx), and fall off together.—Cirsium (Fig. [608]) has a feathery pappus, in other respects it is like Carduus. C. arvense reproduces and passes the winter by means of suckers.—Cynara (Artichoke) has a feathery pappus and large, solitary capitulum, with broad involucral leaves; these have a fleshy base like the receptacle (edible).—Silylum has united filaments. S. marianum (Milk-thistle), has leaves with numerous white spots. Onopordon (Cotton-thistle). Cnicus (C. benedictus) has a large, many-spined thorn on the involucral leaves; pappus trimorphic.—Lappa (Burdock) is easily recognized by the hooked involucral leaves, which assist in the distribution of the fruit; in this respect it differs from the other inflorescences, and also in the fact that the pappus is short, and quickly falls off, without serving as a means of distribution.—Carlina; the external involucral leaves are leafy, thorny, with branched or unbranched spines standing straight out or bent backwards; the internal ones are dry, and prolonged as dry, coloured, radiating scales. The well-developed bristles on the receptacle and edge of the calyx are deeply cleft and lobed.—Centaurea (Knap-weed, Fig. [607]). The ray-flowers are neuter, and generally larger than the disc-flowers; the involucral leaves are regularly imbricate, but are frequently provided at the apex with a dry, chaffy, often lobed, fringed appendage. The attachment of the fruit is lateral. Serratula (Saw-wort).—Carthamus, the outer and inner involucral leaves differ very much.—Echinops (Globe-thistle) is characterised by having “compound capitula,” i.e. there is only one flower in each capitulum, but many such capitula are collected into a spherical head, which at the base may also have a few involucral leaves. The individual capitula have narrow, linear involucral leaves. (There are altogether about 150 species of Compositæ with 1-flowered capitula, all from warm countries.)—Xeranthemum, Staehelina, Jurinea, Saussurea, etc.
2. Mutisieæ, Labiate-flowered Group. Tropical (S. American) forms whose zygomorphic flowers have a bilabiate corolla (2/3). The involucre is nearly the same as in the Thistles.
3. Cichorieæ, Chicory Group (or Ligulifloræ). The flowers are all ☿ and have a ligulate, 5-dentate corolla. The stylar branches are thin and prolonged (Fig. [609] B). Laticiferous vessels occur in the majority (in this feature they resemble the Lobeliaceæ and Campanulaceæ).
A. The pappus is wanting, or it is scale-like, but not long and hairy.—Cichorium (Chicory); capitula with blue flowers, borne singly or a few together in the leaf-axil; there are two whorls of involucral leaves, an outer one of short and radiating, an inner of more numerous, longer and erect leaves; pappus, scale-like.—Lapsana (Nipplewort). The few involucral leaves are nearly of the same size, and persist forming a sort of capsule round the fruits, which are entirely without a pappus. There are only a few flowers in the small capitula.—Arnoseris (Swine’s-succory), Catananche, etc.
B. The pappus is long and hairy (not branched), generally fine and snowy-white. There are no scales on the receptacle. The two genera first considered have beaked fruits.—Taraxacum (Dandelion) (Fig. [606] a); the capitula are many-flowered, and borne singly on the top of a leafless, hollow stalk.—Lactuca (Lettuce) has many small, few-flowered capitula borne in panicles.—Crepis (Hawksbeard).—Hieracium (Hawk-weed) has many imbricate involucral leaves, and a stiff, brittle, brownish pappus.—Sonchus (Sow-thistle); the capitula, when a little old, have a broad base, and are abstricted above in the form of a jug; involucral leaves imbricate; the fruit is compressed, without a beak, ridged. The soft, white pappus falls off collectively.
C. The pappus is feathery and branched; no scales on the receptacle.—Tragopogon (Goat’s-beard) generally has 8 involucral leaves in one whorl. The fruit has a long beak; the rays of the pappus are interwoven in the form of an umbrella.—Scorzonera has fruits like the preceding, but almost without any beak; involucral leaves many, imbricate.—Leontodon (Hawkbit) has a slightly feathery pappus, rays not interwoven; beak absent.—Picris.
D. Long, chaff-like, deciduous scales on the receptacle; pappus feathery.—Hypochœris (Cat’s-ear).
4. Eupatorieæ, Hemp-agrimony Group. All the flowers are most frequently ☿; corollas tubular and regular; the involucral leaves are not stiff and spiny; the receptacle is not covered with stiff bristles. The stylar branches are long, club-like, or gradually tapering. There is no swelling below the stigma.
Eupatorium (Hemp-agrimony); all the flowers are ☿.—Petasites (Butterbur); ray-flowers ♀, disc-flowers ☿ or ♂; sometimes diœcious. Capitula in racemes or panicles. The leaves develop after the flowering.—Tussilago (T. farfara, Colt’s-foot) has a solitary capitulum borne on a scaly, scape-like stem; the ray-flowers are ♀ with ligulate corollas, disc-flowers ♂. The leaves unfold after the flowering. Ageratum, Mikania, Vernonia.