Family Asclepiadaceae
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, or tri-lacunar (? — associated with one or three petiolar traces, not gutter-shaped). 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. Plants hermaphrodite. Pollination entomophilous; often via diptera; 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 ultimate 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). Calyx lobes markedly longer than the tube. Calyx regular; imbricate, or valvate; with the median member posterior. Corolla 5; 1 whorled; appendiculate (with a corona, simple or of separate scales, in only Gymnema, Leptadenia, Oxystelma), or not appendiculate (mostly); gamopetalous (the tube short). Corolla lobes about the same length as the tube, or markedly longer than the tube. Corolla contorted; regular. Androecium 5. Androecial members adnate; united with the gynoecium (forming a gynostegium with it); coherent (via the filaments, forming a short sheath around the style — by contrast with Periplocaceae); 1 adelphous; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; inserted near the base of the corolla tube (at the base); isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous to with sessile anthers. Filaments appendiculate (nearly always, the short filaments ornamented from their external bases with the nectariferous components of an androecial corona of variable form, which is incorporated in the gynostegium), or not appendiculate (Orthanthera only). Anthers connivent (distinct from one another, but individually attached adaxially to the stylehead); basifixed; introrse; bilocular (nearly always), or four locular (Secamoneae only); bisporangiate (usually), or tetrasporangiate (in Secamoneae); appendaged (provided with horny wings and membranous connective appendages 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 (5 genera), or 3-celled (4 genera). Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous (but the carpels united only by their styleheads); synstylous; superior. Carpel (1–)5–50 ovuled (generally numerous). Placentation marginal (ventral). Ovary alternatively interpretable as 2 locular (the separate ovaries being viewed 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 interpretable as axile (ventral in the discrete ‘loculi’, corresponding with ‘axile’ in Apocynaceae). 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; an aggregate (of two carpels), or not an aggregate (of one only, by abortion); dehiscent; comprising a pair of ‘follicles’ with thin papery placental flaps, or commonly only one of the pair developing. Seeds endospermic. Endosperm oily. Seeds conspicuously hairy (with a terminal coma of long, silky hairs); winged (usually, all round), or wingless (Secamoneae). 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 not detected. 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 physiology recorded directly in Asclepias — Krenzer et al. 1975. CAM recorded directly in Caralluma, Ceropegia, Cynanchum, Dischidia, Folotsia, Frerea, Hoodia, Hoya, Huernia, Sarcostemma, Stapelia, Trichocaulon. Anatomy non-C4 type (Asclepias, Caralluma). Geography, cytology. Temperate (rarely), or sub-tropical to tropical. Widespread. N = 11, rarely 10 or 12. Ploidy levels recorded: 2–12. Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Gentianiflorae; Gentianales. Cronquist’s Subclass Asteridae; Gentianales. APG (1998) Eudicot; core Eudicot; Asterid; Euasterid I. APG 3 (2009) Order: Gentianales. Species 2000. Genera 250; Absolmsia, Adelostemma, Aidomene, Amblyopetalum, Amblystigma, Anatropanthus, Anisopus, Anisotoma, Anomotassa, Araujia, Asclepias, Aspidoglossum, Astephanus, Barjonia, Belostemma, Bidaria, Biondia, Blepharodon, Blyttia, Brachystelma, Calotropis, Campestigma, Caralluma, Ceropegia, Cibirhiza, Cionura, Clemensiella, Conomitra, Cordylogyne, Corollonema, Cosmostigma, Costantina, Cyathostelma, Cynanchum, Dactylostelma, Dalzielia, Decabelone, Decanema , Decanemopsis, Dicarpophora, Diplolepis, Diplostigma, Dischidanthus, Dischidia, Ditassa, Dittoceras, Dolichopetalum, Dolichostegia, Dorystephania, Dregea, Drepanostemma, Duvalia, Duvaliandra, Echidnopsis, Edithcolea, Emicocarpus, Emplectranthus, Eustegia, Fanninia, Fischeria, Fockea, Folotsia, Frerea, Funastrum, Genianthus, Glossonema, Glossostelma, Gomphocarpus, Gongronema, Gonioanthelma, Goniostemma, Gonolobus, Graphistemma, Gunnessia, Gymnema, Gymnemopsis, Harmandiella, Hemipogon, Heterostemma, Heynella, Hickenia, Holostemma, Hoodia, X-Hoodiopsis, Hoya, Hoyella, Huernia, Huerniopsis, Hypolobus, Ischnostemma, Jacaima, Janakia, Jobinia, Kanahia, Karimbolea, Kerbera, Labidostelma, Lagoa, Lavrania, Leichardtia, Leptadenia, Lhotzkyella, Lugonia, Lygisma, Macroditassa, Macropetalum, Macroscepis, Mahafalia, Mahawoa, Manothrix, Margaretta, Marsdenia, Matelea, Melinia, Meresaldia, Merrillanthus, Metaplexis, Metastelma, Micholitzea, Microdactylon, Microloma, Microstelma, Miraglossum, Mitostigma, Morrenia, Nautonia, Nematostemma, Neoschumannia, Nephradenia, Notechidnopsis, Odontanthera, Odontostelma, Oncinema, Oncostemma, Ophionella, Orbea, Orbeanthus, Orbeopsis, Oreosparte, Orthanthera, Orthosia, Oxypetalum, Pachycarpus, Pachycymbium, Papuastelma, Parapodium, Pectinaria, Pentabothra, Pentacyphus, Pentarrhinum, Pentasachme, Pentastelma, Pentatropis, Peplonia, Pergularia, Periglossum, Petalostelma, Petopentia, Pherotrichis, Piaranthus, Platykeleba, Pleurostelma, Podandra, Podostelma, Prosopostelma, Pseudolithos, Ptycanthera, Pycnoneurum, Pycnorhachis, Quaqua, Quisumbingia, Raphistemma, Rhyncharrhena, Rhynchostigma, Rhyssolobium, Rhyssostelma, Rhytidocaulon, Riocreuxia, Rojasia, Sarcolobus, Sarcostemma, Schistogyne, Schistonema, Schizoglossum, Schubertia, Scyphostelma, Secamone, Secamonopsis, Seshagiria, Sisyranthus, Solenostemma, Sphaerocodon, Spirella, Stapelia, Stapelianthus, Stapeliopsis, Stathmostelma, Steleostemma, Stelmagonum, Stelmatocodon, Stenomeria, Stenostelma, Stigmatorhynchus, Strobopetalum, Stuckertia, Swynnertonia, Tassadia, Tavaresia, Telminostelma, Telosma, Tenaris, Tetracustelma, Tetraphysa, Thozetia, Toxocarpus, Treutlera, Trichocaulon, Trichosacme, Trichosandra, Tridentea, Tromotriche, Tweedia, Tylophora, Tylophoropsis, Vailia, Vincetoxicopsis, Vincetoxicum, Voharanga, Vohemaria, White-Sloanea, Widgrenia, Woodia, Xysmalobium. Swarupanandan, Mangaly, Sonny, Kishorekumar and Chand Basha (1996). Economic uses, etc. Prized cultivated succulents or vines from Asclepias, Hoya, Araujia, Ceropegia, Stapelia, Caralluma, Decabelone, etc. In dusty pods the milkweed Its hidden silk has spun (Helen Hunt Jackson, ‘September’) |
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