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The families of flowering plants

L. Watson and M.J. Dallwitz

Asclepiadaceae R.Br.

~ Apocynaceae.

Including Stapeliaceae Horan.; 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 vegetative form; sometimes (e.g., Stapelia) ‘cactoid’, with succulent, photosynthetic stems (with the photosynthetic stems otherwise conforming anatomically with the layout characteristic of the rest of the family); with leaves modified as ‘pitchers’ in Dischidia rafflesiana. Leaves well developed, or much reduced. Plants succulent, or non-succulent; autotrophic (usually), or ‘carnivorous’ (? — D. rafflesiana). Trapping mechanism if the ‘pitchers’ of D. rafflesiana function as such, passive. The traps consisting of ‘pitchers’. Perennial. Self supporting, or climbing; when climbing, stem twiners, or root climbers, or scrambling; the twiners twining anticlockwise (Araujia, Ceropegia, Stephanotis). 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 stipulate, or exstipulate (or reduced to colleters). Stipules with colleters (and colleters usually present in the stipular position). Domatia occurring in the family (recorded in 3 genera); manifested as pits, or hair tufts.

General anatomy. Plants with laticifers (non-articulated, branched or not).

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial (e.g., in fleshy leaves of Ceropegia and Hoya). Stomata anomocytic (recorded in Solenostemma, Vincetoxicum and Sarcostemma p.p.), or anisocytic (sometimes in Hoya and Stapelia), or paracytic (mostly, sometimes with the subsidiaries secondarily divided). Hairs present; eglandular (mostly), or glandular (occasionally occurring, in the form of unicellular hemispherical glands, cf. those of Apocynaceae); unicellular, or multicellular. Multicellular hairs uniseriate (mostly), or multiseriate (with shaggy hairs occasionally recorded). Complex hairs absent. Adaxial hypodermis present, or absent. The mesophyll containing crystals. The crystals druses, or solitary-prismatic. Minor leaf veins without phloem transfer cells (Hoya).

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Nodes unilacunar, or tri-lacunar (? — associated with one or three petiolar traces, not gutter-shaped). Primary vascular tissues in a cylinder, without separate bundles; bicollateral. Internal phloem universally present (in the form of either separate strands or a continuous ring). Secondary thickening developing from a conventional cambial ring, or anomalous (commonly in the climbers, variously involving eccentric or unequal development of the xylem, furrowed xylem, cleavage of the wood, areas of unlignified xylem, centripetal development of interxylary phloem). The anomalous secondary thickening from a single cambial ring. Primary medullary rays narrow (typically).

The wood ring porous (in Periploca), or semi-ring porous, or diffuse porous. The vessels small to medium, or large (in lianes). The vessel end-walls simple. The vessels with vestured pits, or without vestured pits; without spiral thickening. The axial xylem with tracheids; with vasicentric tracheids (Leptadenia, Periploca), or without vasicentric tracheids; with fibre tracheids (with small bordered pits), or without fibre tracheids; with libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (predominantly, in Periploca, as scattered cells tending to form numerous short, irregular lines), or paratracheal (usually associated with the vessels in other genra, usually sparse). ‘Included’ phloem present (of the foraminate type, in Leptadenia), or absent. The wood storied (Leptadenia), or partially storied, or not storied (?).

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 units when flowers aggregated, 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, or adnate (? - interpretive problems); 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, phytochemistry. 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). Cyanogenic (very rarely), or not cyanogenic. Alkaloids present, or absent. Arbutin absent. Iridoids seemingly not detected. Saponins/sapogenins usually absent. Proanthocyanidins absent. Flavonols present, or absent; kaempferol, or kaempferol and quercetin. Ellagic acid absent (4 species, 4 genera). Aluminium accumulation not found.

Geography, cytology. Temperate (rarely), 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 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Gentianales (as a synonm of Apocynaceae).

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, Emplectanthus, 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.

General remarks. Evidently related to Apocynaceae sensu stricto (q.v.), but these compiled descriptions show additional differences in assorted ‘esoteric’ characters (wood anatomy, embryology, seedling morphology, iridoids), as well as in details of the androecium and gynoecium and presence of stipule-associated colleters. See 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’)

Illustrations. • Technical details: Asclepias. • Technical details: Cynanchum, Periploca, Stapelia, Vincetoxicum. • Technical details: Schubertia (Lindley). • Absolmsia spartioides, as Astrostemma: Hook. Ic. Pl. 14 (1880–82). • Adelostemma gracillimum: Hook. Ic. Pl. 15 (1883). • Anisopus mannii: Hook. Ic. Pl. 25 (1896). • Araujia sericifera: as Physianthus albens, Bot. Reg. 1759, 1836. • Araujia sericifera: as Physianthus albens: Martius, Nova Gen. et Spec. Pl. Brasiliensium (1824). • Brachystelma johnstonii: Hook. Ic. Pl. 28 (1903). • Calotropis procera: Bot. Reg. 1792, 1836. • Caralluma umbellata, as Boucerosia: R. Wight, Ic. Pl. Indiae Orientalis 2 (1843). • Ceropegia elegans: Bot. Reg. 1706, 1835. • Cynanchum viminale, as 'Sarcostemma brachystigma': Hook. Ic. Pl. 9 (1852). • Cynanchum insigne, as Platykeleba: Hook. Ic. Pl. 25 (1896). • Dittoceras andersonii: Hook. Ic. Pl. 15 (1883). • Edithcolea grandis: Hook. Ic. Pl. 30 (1913). • Hoodia currorii, as Scytanthus: Hook. Ic. Pl. 7–8 (1844). • Hoodia gordoni: Bot. Mag. 102 (1876). • Hoya coriacea: Bot. Reg. 1839, 18. • Huernia somalica: Bot. Mag. 126 (1900). • Parapodium crispum: Hook. Ic. Pl. 28 (1902). • Philibertia grandiflora: Bot. Reg. 29 (13), 1843. • Secamone schimperianus, as Toxocarpus: Hook. Ic. Pl. 29 (1906). • Stapelia gussoneana, = ?: Bot. Reg. 1731, 1835. • Stapelia variegata: Bot. Mag. 26 (1786). • Tassadia trailiana, as Madarosperma: Hook. Ic. Pl. 13 (1877–79). • Trichocaulon piliferum: Bot. Mag. 110 (1884).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 12th September 2017.’.