BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

X. SEED PLANTS

Order Asterales

Perennial or annual herbs and subshrubs, more rarely shrubs, lianas, and small to medium-sized trees. Leaves alternate, less frequently opposite, sometimes whorled, simple, ranging from entire to variously dissected, occasionally reduced, without stipules. A characteristic feature of its representatives is the presence in the phloem of a system of articulated laticifers containing triterpene-rich latex, and/or the presence of a well-developed system of schizogenous secretory ducts.

Some species possess both pronounced laticifers and milk Cells alongside secretory ducts, others have optimally developed secretory ducts with absent laticifers, while milk cells are found in only a few genera. They are also characterized by the accumulation of the reserve carbohydrate inulin, bitter sesquiterpene lactones, and triterpenoids, while lacking Tannins and iridoid compounds. Flowers are gathered into racemose inflorescences—heads or capitula—which, in many cases, form various types of complex inflorescences. The HEAD (capitulum) is typically surrounded by an involucre composed of one or several rows of bracts. Individual flowers of the capitulum, the number of which may be reduced to one, sit on a flat, convex, and sometimes even spindle-shaped common receptacle, more precisely the clinanthium.

In many representatives, individual flowers sit in the axils of scale-like or setaceous bracts, but more often the common receptacle is glabrous. In capitula with homogeneous flowers, all flowers are bisexual, whereas in capitula with heterogeneous flowers, the marginal (ray) flowers are pistillate or neutral (sterile), and the central (disc) flowers are bisexual or functionally staminate. The perianth and androecium are pentamerous, rarely tetramerous. The calyx tube, together with the Base of the corolla tube, is completely adnate to the Ovary, and its free lobes are usually modified into a pappus, which is often reduced or absent.

The corolla belongs to five main types: tubular (actinomorphic and fully sympetalous, five-lobed or five-toothed at the apex); ligulate (tubular at an early stage of development, but during flowering splits longitudinally between the two posterior, or internal, petals and transforms into a ligulate shape); bilabiate (tubular before flowering, but splits longitudinally along two opposite lines passing between the three anterior and two posterior petals, less frequently between four anterior petals and one posterior, with the posterior lip sometimes underdeveloped); radiate (externally resembling a corolla lip); and funnel-shaped. Rarely, the corolla is completely absent (in marginal pistillate flowers).

Stamens are attached to the corolla tube, alternating with the petals; filaments are usually free, sometimes connate into a tube; anthers are typically syngenesious (cohering by their edges); anther bases often bear distinct appendages. The gynoecium consists of two median carpels, syncarpous (paracarpous) with a style bearing a annular or short tubular nectary disc at the base. The stigma is bilobed. In functionally staminate flowers, the style is sometimes undivided. Just below the stigma, the style often bears a collar of hairs (sweeping hairs) that serve to brush out the pollen. The ovary is inferior, unilocular, with a single erect basal ovule. Fruits are achenes, rarely drupaceous, crowned by a persistent pappus, though the pappus is less commonly deciduous or absent.