Stenostelma umbelluliferum

(Schltr.) S.P.Bester & Nicholas

Family : Apocynaceae

 

Flower head

The newest member of the genus Stenostelma, S. umbelluliferum, was moved to this genus recently. Previously known as Schizoglossum umbelluliferum, this plant was after its re-discovery in 2003 (after 109 years), the topic of much debate and frustration amongst both developers and conservationists due to the uncertainty of its Red List status.

Stenostelma umbelluliferum has been overlooked in one of the most abundantly collected grids in the country because of its inconspicuous nature and has thus remained unobserved for many years. It occurs with look-alike taxa that include sprouting grasses, a germinating Ipomoea and Polygala species, which, in the sterile state, all resemble this plant.

Plant

Description
TuberStenostelma umbelluliferum is a small perennial plant, usually not higher than 120 mm, with a carrot-shaped tuber.

The leaves are opposite, lanceolate (lance-shaped, tapering to the point), hairy and revolute (rolled inwards) on the margins.

The inflorescences are on the axillary or terminal nodes. The flowers are cup-shaped, with the edge of the corolla revolute and the tip recurved, and varies from greenish to cream-coloured on the outside and pink on the inside. It has a simple corona that is lime-coloured.

Cup shaped flowers

The fruit is a follicle carried upright, usually solitary in an umbel with longitudinal bands of different shades of green. The seeds are flat and brown and have a white tuft of hairs (coma).

 

The plants are opportunistic, depending on favourable conditions and have been found in flower from September to March, peaking in October to January. After good rains, plants have been found to flower as late as April. Some plants have been found with fruit as early as mid-September, indicating that they may even flower earlier than has been observed.

Conservation status
The species has undergone a number of changes in Red List status in the past three years. It is currently listed as Near-threatened (NT).

MiningIn the Gauteng populations, the main threat is residential and industrial development in and around the known populations. These developments led to the establishment of highly fragmented populations that may not be viable. Another threat is mining. In the North-West, open-cast mining removes topsoil and the habitat is destroyed.

Agriculture is also a threat because the highly fertile soils are utilized for crops. Due to continual loss of suitable habitat, Stenostelma umbelluliferum may need its status changed on the Red List because of its continued decline throughout its distribution range, mainly due to destruction of habitat. Its extent of occurrence and number of populations, however, in the meantime, are responsible for its present being classification. as near-threatened.

Distribution and habitat
This plant is endemic to South Africa in Gauteng, North-West, Free State and KwaZulu-Natal.

The habitat is limited to deep black turf, mainly near drainage lines on vertic soils with high clay content in grassland or savanna, at altitudes between 1 050 and 1 280 m. Plants grow in full sun or light shade. It is a perennial and after fruiting, dies back to a dormant state as an underground tuber. The plants seem to thrive in disturbed areas-probably only because disturbed habitats may favour the easier establishment of seedlings, and, without competition, the spread of the species. Large plants are scarce. Population size varies from a few individuals of less than 10 to large populations of more than 100 plants.

Derivation of name and historical aspects
Stenostelma umbelluliferum was first collected in 1893 by Rudloph Schlechter while on a collecting trip in South Africa. He found a single plant of this species on the plains at the foot of the Magaliesberg. With the bombing of the Berlin Herbarium during World War II, the type (and at that time the only specimen) was probably destroyed and the species remained obscure.

Rudolph Shlechter is the author of the genus name Stenostelma and although he did not specifically state the origin of the name, it is probably derived from the two Greek words stenos, that means narrow or slender, and stelma, meaning crown. This refers to the shape of the corona with a long, drawn-out process or horn in the type species of the genus, S. capense.

The specific name umbelluliferum is assumed to allude to the way the flowers are carried in the inflorescence, typically forming a globose or subglobose umbel.

There are currently four species in this genus. Stenostelma umbelluliferum is easily distinguished from the other species by its size: it is the smallest plant (38-200 mm) with the smallest flowers and the corona does not have any horns, teeth or extensions. The other species are S. capense, S. corniculatum and S. carinatum. The first two are widely distributed and the latter very restricted to a few large populations in the Kokstad area.

Ecology
Depth of the tuber below the soil surface varies greatly, from directly to about a depth of 20 cm. In the dry season, the turf dries out, and cracks of up to 0.5 m have been observed. The shape of the tuber is specifically adapted to the drying of the soil and prevents the tuber from being severed when the soil dries out. At the time of the year that this happens, the plants also die back and become dormant till springtime.

Pollinators of the group Miridae have been seen on the plants.

The seeds are distributed by wind and the coma makes it possible to be carried by air currents. The establishment of young plants seems to be relatively successful.

Uses and cultural aspects
Discussions with various farm workers throughout the distribution range revealed that the plant is even unknown to them and those who recognized it from photographs or live plants do not know of any traditional use of the plant.

Flowerhead

Growing Stenostelma umbelluliferum

Because of the specific habitat requirements, milky latex and small size of the plant, it does not seem to have horticultural potential. It would probably only interest those with a passion for this group of plants. About six mature plants (of a total of 30) that have been removed from development sites have survived in pots for three years. Of these, only two have flowered, but they did not produce fruit (probably due to the absence of the specific pollinator and because they are outside its natural environment).

Fresh seeds obtained from plants from the natural environment germinated well, but the survival rate was almost zero ( I am not an expert!). Young seedlings grow very quickly and form a long primary root before growth of the above-ground stems and leaves take place. Very few large plants have been found and most plants seem to be relatively young. Seed set is very good.

Various parasitic infestations by insects were observed, in many cases causing the plant to wilt and terminate above-ground growth. These include oleander aphids, the milkweed bug and net-winged beetles.

Almost no information about the biology of the plant is known and this may present an opportunity for further study.

References and further reading

  • Bester, S.P. & Nicholas, A. 2007. Transfer of Schizoglossum umbelluliferum to Stenostelma, and its neotypification (Apocynaceae-Asclepiadoideae). Bothalia 37: 48-51.
  • Bester, S.P., Nicholas, A. & Condy, G. 2007. Stenostelma umbelluliferum. Flowering Plants of Africa 60: 96-103.
  • Bester, S.P. & Victor, J.E.. 2005. Elusive Schizoglossum rediscovered in Pretoria after 109 years. The Conservation leaflet 3, September 2005: 8. South African National Biodiversity Institute, Pretoria.
  • Bester, S.P. & Victor, J.E.. 2005. Schizoglossum umbelluliferum : an unusual milkweed re-collected in Pretoria after 109 years. Veld & Flora Vol. 91 No.4 December 2005 : 166.

 

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Author

S.P. Bester
National Herbarium, Pretoria
March 2008

 

 

 

 

 

 

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