Asclepias bicuspis N.E.Br.
Common names: none known
Thought to be extinct and known from only six collections, two of which were collected over a hundred years ago, Asclepias bicuspis, was unexpectedly rediscovered in 1998 and then again during the past two field seasons.
Asclepias bicuspis is a small (up to 25 cm), hairy, single stemmed plant with 4 to 6 pairs of opposite leaves, approximately 5 cm long and 4 cm wide with the margins rolled under. Typical of the Apocynaceae, the species contains milky latex.
The greenish-yellow, star-shaped, scentless flowers are borne in 5 to 8 flowered umbels (clusters) in early summer, October and November. Diagnostic features include the two long cusp-like corona lobe appendages, triangular shaped anther wings and wing like anther appendages which have a wide but shallow apical cleft. The oblong shaped pollinia (structures containing the pollen grains) are also a unique characteristic that can be used to identify this species.
Asclepias bicuspis is listed as Critically Endangered in the Red List of South African Plants (Raimondo et al 2009) because its habitat has been heavily impacted by agriculture, afforestation, the construction of the Midmar Dam and urban expansion. Asclepias bicuspis was presumed extinct in the wild by Asclepias expert Ashley Nicholas after several unsuccessful collecting trips to historical localities. It was unexpectedly recollected by Greene in 1998. During the 2009-2010 and 2010-2011 field-seasons, the species was found at 3 localities by the by the Custodians of Rare and Endangered Wildflowers (CREW) Programme: KZN node. This demonstrates the importance of constant monitoring.
Distribution and habitat
The species grows only in the highly transformed Endangered KwaZulu-Natal Midlands Mistbelt Grassland at an altitude of 1200-1500 m. Plants can be found in annually burnt grasslands, including firebreaks, in full sun and well-drained soil, on rocky doleritic hillsides. It is never abundant, and plants have a scattered distribution in known localities.
Derivation of name and historical aspects
Asclepias is named after the Greek doctor Aesculapius who was immortalized in ancient mythology as a god of medicine. The specific epithet bicuspis is a reference to the two long, slender, thread-like corona lobes.
Flowers of Asclepias bicuspis are waxy, making it difficult for pollination. Hence the flowers face downward to allow for better grip of insects on the corona surface. The corona lobes act as guides for an insect's foot to the pollenia and after nectar is obtained, the insect's foot pulls these pollinia with it, and carries it to the next flower visited. Although A. bicuspis nectar is well sought out, the specific pollinators of these tiny flowers are not known.
Not much is known about this rare species.
Growing Asclepias bicuspis
The root tuber is very deep, indicative of an extremely long-lived species. However, any damage to the tuber will result in the death of the plant. Propagation through seeds or micro-propogation might be successful.
- Nicholas, A. pers.comm. School of Biological and Conservation Sciences, University of KwaZulu-Natal.
- Nicholas, A. 1982. Taxonomic studies in Asclepias (Asclepiadeae) with particular reference to the narrow-leaved species in southern Africa: 393-401. MSc, University of Natal.
- Nicholas, A. 1999. A taxonomic reassessment of the subtribe Asclepiadinae (Asclepiaceae) in Southern Africa: 206-208. PhD, University of Durban-Westville, Durban.
- Raimondo, D et al.(eds) 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria
Custodians of Rare and Endangered Wildflowers
(CREW): KZN node
Plant Type: Perennial
SA Distribution: KwaZulu-Natal
Soil type: Sandy, Loam
Flowering season: Early Summer
Flower colour: Green, Yellow
Aspect: Full Sun
Gardening skill: Challenging