~ Asclepiadaceae, Apocynaceae
Habit and leaf form. Shrubs (or shrublets), or lianas (commonly), or trees (rarely), or herbs (rarely); laticiferous. The herbs perennial; sometimes tuberous. Self supporting, or climbing; the climbers stem twiners. Mesophytic, or xerophytic. Leaves opposite; petiolate; simple; epulvinate. Lamina entire; linear to obovate; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire.
General anatomy. Plants with laticifers (non-articulated, branched or not).
Leaf anatomy. Stomata paracytic, or anomocytic, or anisocytic.
Lamina with secretory cavities (laticifers accompanying the veins). Secretory cavities containing latex. Minor leaf veins without phloem transfer cells (Periploca).
Stem anatomy. Secretory cavities present. Primary vascular tissue bicollateral. Internal phloem present. Secondary thickening developing from a conventional cambial ring, or anomalous; via concentric cambia, or from a single cambial ring (?). `Included' phloem present, or absent (?). Wood storied (Periploca); parenchyma apotracheal (predominantly, in Periploca), or paratracheal (?).
Reproductive type, pollination. Hermaphrodite (usually), or dioecious. Entomophilous. Pollination mechanism conspicuously specialized (with pollen transference involving `translators' - spoon- or funnel-shaped structures arising from the stylehead between the anthers, which conceal the stigmatic surfaces from pollinators and into each of which the granular pollen from adjacent half-anthers is shed. A sticky disk on the base of the translator adheres to the head of a visiting insect, which carries off the translator and its pollen contents).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in cymes. The terminal inflorescence unit cymose. Inflorescences cymose, neither umbelliform nor racemose. Flowers bracteate; small (usually), or large (and showy, rarely); regular; 5 merous; cyclic; tetracyclic. Free hypanthium present. Hypogynous disk absent.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; gamosepalous (the tube short); regular; imbricate, or valvate. Corolla 5; 1 whorled; appendiculate (in that a corona may arise from the region of junction between filaments and corolla), or not appendiculate; gamopetalous; contorted (usually), or valvate; regular.
Androecium 5. Androecial members free of the perianth (on the hypanthium), or adnate (to the base of the corolla tube); free of the gynoecium; coherent (via the anthers); 1 - adelphous; 1 - whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous. Filaments appendiculate (usually), or not appendiculate (in female plants). Anthers cohering (into a sheath, and adherent to the stylehead); basifixed; non-versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged (usually), or unappendaged. The anther appendages apical, or dorsal, or lateral. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or T-shaped, or linear. Anther wall initially with one middle layer, or initially with more than one middle layer; of the `dicot' type. Tapetum glandular. Pollen shed in aggregates; in tetrads (these variously tetrahedral, rhombiodal, linear, etc., and the tetrads readily separating, only weakly coherent into pollinia). Pollen grains aperturate; 3-6 - aperturate; porate; 2-celled, or 3-celled.
Gynoecium 2. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylous (the separate carpels united only by the common stylehead); superior. Ovary 2 locular (the separate ovaries being viewed as the `locules' of a `syncarpous' gynoecium). Gynoecium median; stylate. Styles 2; partially joined (free below, but joined at the distended stylehead, cf. Asclepiadaceae). Placentation marginal in the discrete ovaries. Ovules 5-50 per locule (to `many'); pendulous; anatropous; unitegmic; pseudocrassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation nuclear. Embryogeny solanad.
Fruit non-fleshy; multiple (the units usually paired), or not multiple (by abortion of one of them); dehiscent; of two follicles, or one undeveloped. Seeds endospermic. Endosperm oily. Seeds conspicuously hairy (with a terminal coma of long, silky hairs). Embryo well differentiated. Cotyledons 2. Embryo straight.
Physiology, biochemistry. Not cyanogenic. Alkaloids present. Iridoids absent (?). Proanthocyanidins present; cyanidin. Ellagic acid absent (Periploca). Arbutin absent. Saponins/sapogenins absent. Aluminium accumulation not found. C3. C3 recorded in Cryptostegia.
Geography, cytology. Holarctic, Paleotropical, and Cape. Temperate to tropical. Old World, especially tropical Africa. X = 9-12.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren's Superorder Gentianiflorae; Gentianales. Cronquist's Subclass Asteridae; Gentianales. Takhtajan's Subclass Asteridae; Gentiananae; Gentianales. Species 200. Genera 45-50; Asterostemma, Atherolepis, Aechmolepis, Baseonema, Camptocarpus, Cryptolepis, Cryptostegia, Curroria, Decalepis, Ectadium, Epistemma, Finlaysonia, Gonglyosperma, Harpanema, Hemidesmus, Ischnollepsis, Macropelma, Meladerma, Oxystelma, Parquetia, Periploca, Raphionacme, Streptocaulon, Tacazzea, Triodoglossum, Utleria, Zygostelma, etc.
Economic uses, etc. Some cultivated ornamentals (Periploca), and Cryptostegia has been used as a source of natural rubber.
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