Ceropegia decidua subsp. pretoriensis

From Flowering plants of Africa. 1993. Vol. 52: Plate 2073 (Ceropegia decidua subsp pretoriensis). National Botanical Institute, Pretoria.

Flowering season: December-April

Habitat: Direct sunshine or shaded situations, rocky outcrops of the quartzitic Magaliesberg mountain series, in pockets of soil among rocks, in shade of shrubs and low trees, can be seen twining around grass spikes.

Conservation status: Vulnerable

 

ARTIST.— Gillian Condy.

 

Plants may be found growing in direct sunshine or in shaded situations. Tubers are initially turnip-shaped, but mature into a disc-like structure with white flesh. This tuber lies just below the humus level (usually sandy leaf mould). On rare occasions two or more young tubers may be found connected in series. From the tuber one or two long, thin stems are produced. The degree to which these stems climb depends on the support offered by the surrounding vegetation. This factor also governs the size of the basal leaves and length and leafiness of the flowering stem. Generally the above-ground parts of the plant do not die away completely during the dry season, and regrowth is initiated only after good rains. Most plants usually flower between January and February, although under ideal conditions plants have been recorded flowering as early as September and as late as April. Fruit generally starts to appear between February and April and, according to Bruyns, mature seeds are usually produced between May and July.

This plant is a Pretorian endemic. All present National Herbarium collections come from the 2528C and 2528D quarter degree grids (see map). They were all found growing at an average altitude of about 1 440 meters. Although still found within the Pretoria municipal boundaries, its habitat remains under threat from increasing urbanization. The introduction of exotic species into the rocky, hilly parts of Pretoria is at present the main culprit and to a lesser degree the erection of houses is also a threat. Although not in immediate danger of extinction, this plant’s long term survival in its native habitat is doubtful.

The artist and author would like to thank Mr A. Hitchcock for his help and enthusiasm. Along with the referees we would also like to thank Dr Peter Bruyns for his invaluable comments and additions to the original manuscript.

 

To deal adequately with the variation exhibited by Ceropegia decidua, Dyer found it necessary to create two subspecies: subsp. decidua and subsp. pretoriensis. This latter subspecies is illustrated here. In 1983 Dyer saw no reason for giving these two taxa more than subspecific recognition, even hinting that some taxonomists may find this distinction undesirable. Taken within the context of the genus, the characters used to separate these two taxa are not conservative in an evolutionary sense and are therefore taxonomically unimportant. In my experience they do not warrant specific rank under any currently held species concept. However, if we were to sink the two taxa we would be losing interesting morphological, phytogeographical and ecological information. Dyer’s choice of rank is therefore considered ideal, and I have chosen to uphold his subspecific status for these two taxa.

Having committed myself to Dr Dyer’s taxonomic concepts I must also state that Dr Peter Bruyns has kindly pointed out that the classification accepted by me here may be erroneous and that Ceropegia decidua subsp. pretoriensis may, in fact, be conspecific with C. fortuita R.A. Dyer. and have little to do with C. decidua subsp. decidua. Dr Bruyns has worked on Ceropegia for many years now and his field work on the genus is almost without rival. I am inclined to agree that he may have a valid point concerning the taxonomic position of C. decidua subsp. pretoriensis, but have decided to leave the final decision and the valid publication of his findings to him.

Subsp. decidua can be distinguished from subsp. pretoriensis by the fact that it usually (but not always) drops its leaves before flowering. The corolla lobes are pinched or constricted in the middle only and broaden abruptly at their apices where they unite to form a small canopy. The lobe below the central constriction is flat on the inner surface and the margins are folded tightly against the outer face of the lobe; adjacent lobes touch each other along these folds for some

distance above their bases. Also, the corolla has five ridges running down its length, these ridges starting just below the lobe sinuses. Subsp. decidua occurs in what Acocks (1988, Veld types of South Africa, 3rd edn, Memoirs of the Botanical Survey of South Africa No. 57) referred to as Bushveld, in particular the thornveld components of this broad vegetation type. Subsp. decidua may be found sporadically from the northern Transvaal to the lower-lying, warmer parts of Swaziland.

In contrast, subsp. pretoriensis has persistent leaves, while the corolla lobes are loosely folded along the midrib for their whole length, which is especially noticeable in the lower two thirds or at least below the middle of the lobe. The lobes are not reflexed tightly towards the base and adjacent lobes do not touch, except at their very base. Although united at the tips, the lobes do not form a canopy and the corolla tube is without ridges. According to Bruyns (1981), subsp. pretoriensis is confined to rocky outcrops of the quartzitic Magaliesberg mountain series and will not be found growing on dolerite, dolomite or in flat areas.


 

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