~ Apocynaceae
Excluding Periplocaceae
Habit and leaf form. Herbs, or lianas, or shrubs, or trees (rarely); laticiferous. `Normal' plants, or switch-plants, or plants of very peculiar form; somtimes `cactoid'. Leaves well developed (with `pitchers' in Dischidia), or much reduced. Plants succulent, or non-succulent. Perennial. Self supporting, or climbing; when climbing stem twiners, or scrambling. Mesophytic, or xerophytic. Leaves opposite (decussate, usually), or whorled (rarely, and rarely spiral); `herbaceous', or fleshy, or membranous, or modified into spines; simple. Lamina entire (often reduced); one-veined, or pinnately veined, or pinnately veined to palmately veined. Leaves usually exstipulate. Domatia recorded (in 3 genera); represented by pits, or hair tufts.
General anatomy. Plants with laticifers (non-articulated, branched or not).
Leaf anatomy. Stomata anomocytic, or anisocytic, or paracytic.
Minor leaf veins without phloem transfer cells (Hoya).
Stem anatomy. Cork cambium present; initially superficial. Nodes unilacunar. Primary vascular tissue often bicollateral. Internal phloem usually present. Secondary thickening developing from a conventional cambial ring, or anomalous; from a single cambial ring. `Included' phloem present, or absent. Xylem with fibre tracheids, or without fibre tracheids; with vessels. Vessel end-walls simple. Vessels with vestured pits. Wood storied (Leptadenia), or partially storied, or not storied (?); parenchyma apotracheal (usually sparse).
Reproductive type, pollination. Hermaphrodite. Entomophilous; often via diptera. Pollination mechanism conspicuously specialized (involving trapping of insects' legs or probosces between the osmotically elastic anther wings, and withdrawal entailing capture of the pollinia by means of `sutured corpuscular pollen carriers').
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in `inflorescences'. The terminal inflorescence unit usually cymose (often umbelliform), or racemose (rarely). Flowers fragrant, or malodorous, or odourless; regular; 5 merous; cyclic; tetracyclic. Hypogynous disk absent.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; usually gamosepalous (at the base); regular; imbricate, or valvate; with the odd member posterior. Corolla 5; 1 whorled; appendiculate (with a corona, simple or of separate scales), or not appendiculate; gamopetalous (the tube short); contorted; regular.
Androecium 5. Androecial members adnate (to the base of the corolla tube); united with the gynoecium (forming a gynostegium with it); coherent (in a short sheath around the style - by contrast with Periplocaceae); 1 - adelphous; 1 - whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous; filantherous to with sessile anthers. Filaments appendiculate (the short filaments ornamented from their external bases with the nectariferous components of a corona of variable form, which is incorporated in the gynostegium). Anthers cohering; basifixed; introrse; bilocular, or four locular; bisporangiate (usually), or tetrasporangiate (in Secamone); appendaged (provided with horny wings, contributing to the coronal complex). Endothecium developing fibrous thickenings (rarely), or not developing fibrous thickenings (a thick, undifferentiated wall being common). Microsporogenesis successive, or simultaneous. The initial microspore tetrads linear. Anther wall initially with one middle layer; of the `basic' type, or of the `dicot' type. Tapetum glandular. Pollen shed in aggregates; in the form of pollinia (one or two per theca). Pollen grains 2-celled, or 3-celled.
Gynoecium 2. Carpels reduced in number relative to the perianth. Gynoecium syncarpous (but the carpels united only by their styleheads); synstylous; superior. Ovary 2 locular (insofar as the separate, unilocular ovaries and be regarded as the `locules' of a `syncarpous' gynoecium). Gynoecium median; stylate. Styles 2; partially joined (free below, but united by the dilated stylehead, which has lateral stigmatic surfaces alternating with the stamens). Stigmas wet type, or dry type; papillate, or non-papillate; Group II type and Group IV type. Placentation marginal in the discrete ovaries. Ovules (1-)5-50 per locule (generally more or less numerous); pendulous; anatropous; unitegmic; pseudocrassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral (usually), or persistent (Ceropegia, Cynanchum). Synergids pear-shaped (sometimes with filiform apparatus). Endosperm formation nuclear. Embryogeny solanad.
Fruit non-fleshy; multiple (of two carpels), or not multiple (of one only, by abortion); dehiscent; comprising a pair of `follicles', or commonly only one of the pair developing. Seeds endospermic. Endosperm oily. Seeds conspicuously hairy (with a terminal coma of long, silky hairs). Cotyledons 2. Embryo chlorophyllous (4/7); straight.
Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Cyanogenic (very rarely), or not cyanogenic. Alkaloids present, or absent. Iridoids seemingly absent. Proanthocyanidins absent. Flavonols present, or absent; kaempferol, or kaempferol and quercetin. Ellagic acid absent (4 species, 4 genera). Arbutin absent. Saponins/sapogenins usually absent. Aluminium accumulation not found. C3 and CAM. C3 recorded in Asclepias - Krenzer et al. 1975. CAM recorded in Caralluma, Frerea, Huernia, Hoya, Stapelia, Trichocaulon. Anatomy non-C4 type (Asclepias, Caralluma).
Geography, cytology. Temperate (rarely), or sub-tropical to tropical. Widespread.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren's Superorder Gentianiflorae; Gentianales. Cronquist's Subclass Asteridae; Gentianales. Takhtajan's Subclass Asteridae; Gentiananae; Gentianales. Species 2000. Genera 235; Araujia, Asclepias, Brachystelma, Caralluma, Ceropegia, Decabelone, Cynanchum, Dischidia, Ditassa, Gonolobus, Hoya, Huernia, Marsdenia, Matelea, Oxypetalum, Secamone, Stapelia, Tylophora, etc.
Economic uses, etc. Prized cultivated succulents or vines from Asclepias, Hoya, Araujia, Ceropegia, Stapelia, Caralluma, Decabelone, etc.
Illustrations. ascle552.gif ascle627.gif
Additional, to be intercalated. The twiners twining anticlockwise (Araujia, Ceropegia, Stephanotis).
