Asclepias
Introduction
Members of the genus Asclepias (as most of the taxa in the family Apocynaceae in the broad sense, subfamily Asclepiadoideae), are an interesting group because of their extra-ordinary fusion of the male and female parts of the flowers and the development of interesting pollination mechanisms and development of fascinating flowers.
Figure 1. Asclepias woodii. (Photo A. Shuttleworth)
Description
Description
Perennial, re-sprouting herbs from a deep-seated underground tuber or woody rootstock. All parts exude milky latex when bruised. Plants usually small (less than 400 mm tall), with their stems and spreading along the soil surface (prostrate) or erect; branched or not.
Figure 2. Opposite, and decussate, leaves in Asclepias. (A) Asclepias albens; (B) Asclepias cucullata. (Photos SP Bester)
Leaves opposite; blade with various shapes but usually linear, lanceolate or broadly ovate; base cordate, truncate or cuneate with an acute tip; margin usually entire and mostly rolled in on the underside.
The flowers are usually aggregated into an inflorescence, known as an umbel.
Figure 3. Inflorescences in Asclepias species. (A) Asclepias densiflora (Photo SP Bester); (B) Asclepias vicaria (Photo SP Bester); (C) Asclepias crassinervis (Photo J Kirkel); (D) Asclepias macropus (Photo A Shuttleworth); (E) Asclepias crispa. (Photo A Shuttleworth)
Figure 4. Some parts of Asclepias adscendens, a typical Asclepias flower.
The flower has 2 carpels, but after pollination one is usually aborted in favour of the other that fully develops into a mature fruit called a follicle.
Figure 5. Fruit of some Asclepias species. (A) Asclepias albens (Photo SP Bester); (B) Asclepias densiflora (Photo SP Bester); (C) Asclepias vicaria (Photo HM Steyn); (D) Asclepias aurea (Photo SP Bester); (E) Asclepias gibba (Photo SP Bester)
Conservation Status
Status
Of the 45 species (48 taxa) of this genus that occur in the Flora of southern African Region, most of the taxa were assessed with conservation status of Least Concern (LC). There are, however, 19 taxa (40%) of conservation concern: 4 Rare; 2 Near Threatened (NT); 5 Data Deficient (DD); 1 Vulnerable (VU); 3 Critically Rare (CR) and 3 Endangered (EN). Most of these taxa occur in grassland and savanna habitats and are threatened because of destruction of their natural environment by large-scale agriculture, mining and urban development. It is also interesting that in the southern African region, most of the members of this genus occur in areas of summer rainfall.
Distribution and habitat
Distribution description
In the current circumscription of the genus it is native to the Americas and sub-Saharan Africa. It has been indicated that the species from the Americas and those from Africa are only of ancient affiliation and as the first member was described from America, the African species should be assigned a new generic name(s). These new combinations have not yet been made and for now they all are placed in the genus Asclepias. In Africa the genera are closely related. Gomphocarpus is separated from Asclepias mainly based on having a rootstock instead of a deep-seated tuber.
In southern Africa it is found in various habitats within grasslands, savanna and wetlands, mainly in the summer rainfall areas with very few species from the winter rainfall areas.
Derivation of name and historical aspects
History
The generic name Asclepias is derived from the Greek doctor Aesculapius who, according to the ancient mythology, was immortalised as the god of medicine.
Ecology
Ecology
The fusion of the male and female parts of the flowers renders the flowers complicated, with pollination usually performed by specific pollinators, which need to remove the pollen that is aggregated in pollinia consisting of 2 masses of pollen joined by caudicles to a clip. The clip attaches to the mouth parts, or even a leg, of a possible pollinator and needs to be deposited in the guiderail of another flower for successful pollination.
Figure 6. Some parts of Asclepias brevicuspis flower. (Photo SP Bester)
The follicles (fruits) burst longitudinally to release seeds that have a tuft of spreading hairs on one side (coma), which helps the seeds get airborne for dispersal.
Figure 7. Asclepias gibba fruit (follicle) splitting open and releasing seed with coma. (Photo SP Bester)
Uses
Use
Many of the species are used as medicine or entire plants or parts thereof as famine food plants.
African species are not cultivated, nor are they available from any nurseries.
Growing Asclepias
Grow
Flowers and fruits of members of the genus are very attractive, but relatively short lived and these plants are mostly vegetative. Indigenous species are not at all grown in gardens nor available from nurseries in South Africa (to the author’s knowledge). Species that are cultivated are those like Asclepias currasicava which is introduced from Mexico to South Africa.
Figure 8. Asclepias curassavica, a species native to Central and Northern parts of South America, is not uncommon in South African gardens and sometimes available from nurseries
If plants are cultivated, it is usually by interested connoisseur growers and collectors of exotic plants, rather than as ornamental garden subjects. Plants could be grown from wild-collected seed, which germinate relatively easily, but it is difficult to maintain a plant in cultivation until it flowers. Fresh seed should be sown in a light sandy to humic soil substrate and kept moist until germinated (usually about a week to sixteen days).
Species
Asclepias adscendens (Schltr.) Schltr.
Conservation status: Least Concern (LC).
Perennial herb, 100–200 mm tall. Leaves linear-lanceolate to ovate; umbels solitary and terminal with 12–15 flowers. Peduncles 5–65 mm long. Corolla lobes reflexed or spreading reflexed with upcurved tips. Flowers white to pinkish or purplish. Plants flower in spring to early summer (August to December); in grassland. Widely distributed in Lesotho, Mozambique, South Africa (Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga and North West Provinces); also Eswatini and Zimbabwe.
Asclepias albens (E.Mey.) Schltr.
Common names: cartwheels (Eng.); tshalale (TshiVenda).
Conservation status: Least Concern (LC).
Perennial erect or decumbent herb, 250–500 mm tall, unbranched or branched at the base. Leaves ovate to ovate-lanceolate, base subcordade to broadly rounded, bristly hairy on both sides. Umbels solitary, terminal, robust (up to 80 mm in diam.) with 15–30 flowers. Peduncles 40–100 mm long. Corolla lobes reflexed, glabrous inside. Flowers white or light purple or pinkish. Plants flower in midsummer (December to January) and grow in grassland. The young leaves are eaten as a spinach. Widely distributed in the eastern part of southern Africa in Lesotho, South Africa (Eastern Cape, Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga and North West Provinces); also Eswatini.
Asclepias aurea (Schltr.) Schltr.
Conservation status: Least Concern (LC).
Perennial herb, 140–500 mm tall. Leaves long and linear, glabrous; umbels axillary and terminal, usually with 4 (rarely 5–8) flowers. Relatively long scapose peduncles 40–140 mm long. Corolla lobes reflexed or spreading, canescent inside. Flowers yellow or white; corona white, yellow or purple with white sides; flowers in spring to autumn (August to May); grows on grassy slopes or rocky hillsides. Used medicinally as an emetic.
Asclepias brevipes (Schltr.) Schltr.
Common name: bokhorinkie (Afr.).
Conservation status: Least Concern (LC).
Perennial decumbent herb; leaves linear, scabrous. Umbels terminal and axillary, usually with 4 flowers; peduncle 10–50 mm long; corolla lobes spreading, canescent inside, pubescent outside. Flowers yellow-brown tinted white or green; corona reddish brown, purple or white; flowers in spring to early summer (September to December). Usually found in burnt veld on hillsides. Restricted to the northern parts of South Africa (Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga and North West Provinces).
Asclepias crispa P.J.Bergius var. crispa.
Common name: bitterwortel (Afr.).
Conservation status: Least Concern (LC).
Perennial herb 150–400 mm tall; leaves crisped-wavy, linear to lanceolate, truncate, rounded or cuneate at base; scabrous or pubescent. Umbels solitary, terminal or 2–4 racemosely arranged, pedunculated, with 7–40 flowers; corolla lobes reflexed, glabrous on both sides or pubescent outside. Flowers dull green or purplish tinted inside, brown purplish outside; corona greenish or with purple outer margin. Usually flowers in September. Decoctions or infusions of the root is used as a diuretic and purgative medicine. Reported to be toxic to livestock.
Asclepias cucullata (Schltr.) Schltr. subsp. cucullata.
Conservation status: Least Concern (LC).
Perennial herb, erect to decumbent. Leaves linear to narrowly lanceolate; corolla lobes spreading with tips curving up; scabrous to pubescent outside, canescent inside. Corona lobes erect, shorter than or only slightly exceeding the staminal column, cucullate part of corona lobes ± as long as broad. Flowers purple or mauve, white to grey. Plants usually flower in spring to early summer (September to December). Grows in open mountain grassland. Mainly along the southern Cape coast but also other parts of South Africa (, Gauteng, Mpumalanga and Eastern and Western Cape Provinces); also Eswatini.
Asclepias cultriformis (Harv. ex Schltr.) Schltr.
Conservation status: Least Concern (LC).
Perennial herb 150–300 mm tall. Leaves oblong, lanceolate or ovate-lanceolate. Corolla lobes ascending-spreading, pubescent outside, pubescent to densely white-hairy at tips and along margins, glabrous inside. Corona lobes with compressed, erect processes or horn within cavity. Flowers green or dark purple-brown; corona white with violet spot on back near apex and violet at base. Plants flowers December to February. Grows in grassland. Distributed in Lesotho, South Africa (Eastern Cape, Gauteng, KwaZulu-Natal, Limpopo and Mpumalanga Provinces); also Eswatini.
References
- Fox, F.W. & Norwood Young, E. 1982. Food from the veld: edible wild plants of southern Africa. Delta Books, Cape Town.
- Germishuizen, G. & Fabian, A. 1997. Wild flowers of northern South Africa. Fernwood Press, Vlaeberg, Cape Town.
- Goyder, D.J. 2009. A synopsis of Asclepias (Apocynaceae: Asclepiadoideae) in tropical Africa. Kew Bulletin 64: 369–399.
- Leistner, O.A. (ed.). 2000. Seed plants of southern Africa: families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Plants of the World Online. http://www.plantsoftheworldonline.org/
- Pooley, E. 1998. A field guide to wild flowers Kwazulu-Natal and the eastern region. Natal Flora Publications Trust, Durban.
- Raimondo, D. et al. 2009. Red list of South African plants. Strelitzia 25. SANBI (South African National Biodiversity Institute), Pretoria.
- Retief, E. & Herman, P.P.J. 1997. Plants of the northern provinces of South Africa: keys and diagnostic characters. Strelitzia 6. National Botanical Institute, Pretoria.
- Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35. Government Printer, Pretoria.
- Van Wyk, B.-E. & Gericke, N. 2000. People's plants, a guide to useful plants of southern Africa. Briza Publications, Pretoria.
- Van Wyk, B. & Malan, S. 1997. Field guide to the wild flowers of the Highveld. 2nd edition. Struik Publishers, Cape Town.
- Watt, J.M. & Breyer-Brandwijk, M.G. 1962. The medicinal and poisonous plants of southern and eastern Africa , edn 2. Livingstone, Edinburgh & London.
Credits
Stoffel Petrus Bester
Biosystematics and Collections Division: National Herbarium
February 2020
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