Anacampseros decapitata Burgoyne & J. van Thiel, a representative of the predominantly succulent family Portulacaceae, was recently described from the North West Province of South Africa. It is most closely related to A. subnuda Poelln., with which it co-occurs. It differs from the latter in having shiny-smooth, near-globular leaves, and a unique vegetative distribution mechanism, in that the tips of vegetative stems become dislodged and blow along the ground like tumbleweeds.
Introduction
The Portulacaceae are represented in South Africa by just over 50 species, distributed among seven genera (Table 1). Until recently, depending on which source is followed, the well-known portulacaceous genus Anacampseros L. consisted of 15 (Glen 2003) or 16 species (POSA 2009) in South Africa. These numbers must now be increased by at least one as a new species of Anacampseros, A. decapitata Burgoyne & J. van Thiel, was recently described from the country (Burgoyne & Van Thiel 2010). Most of the species of Anacampseros occur in the western and central karroid parts of South Africa, with only a few extending in an eastern and northeastern direction into the grasslands and savanna regions, from where A. decapitata was collected.
Table 1.
Portulacaceae in South Africa (POSA 2009). Introduced taxa are marked*.
The classification of Anacampseros has been subject to several changes after its revision by Gerbaulet (1992) about 20 years ago, with first the split into three genera Anacampseros, Grahamia Gillies ex Hook. & Arn. and Avonia (E. Mey. ex Fenzl) G. D. Rowley by Rowley (1994, 1995), and then the subsequent proposed synonymisation of Avonia by Gerbaulet & Struck (1995). A review of these changes has been given in the literature by Williamson (1997). At present the genera Anacampseros and Avonia are accepted by most authors working in South Africa (Glen 2003; Mabberley 2008).
To date, only two taxa of Anacampseros have been recorded in Gauteng and the neighboring North West Province of South Africa (POSA 2009), A. subnuda Poelln. and A. filamentosa (Haw.) Sims. subsp. filamentosa. Gerbaulet (1992) distinguished these two taxa on seed characters: in A. filamentosa the seeds are aculeate (armed with prickles) or echinate (densely covered with rigid hairs or small prickles) while in A. subnuda subsp. subnuda they are colliculate (covered in small rounded protuberances). Rowley (1994) distinguished them on the glabrous (smooth) older leaves in A. subnuda, as opposed to the consistently tomentose (densely hairy) leaves of A. filamentosa. A. subnuda consists of two subspecies, subsp. subnuda and subsp. lubbersii (Bleck) Gerbaulet, the latter recorded from eastern Gauteng and Mpumalanga Province. These subspecies are distinguished on the axillary bristles protruding, and longer than the tomentose leaves in the former, and shorter bristles, hidden by the glabrous, shiny, rugose (wrinkled) leaves in the latter (Bleck 1984). Furthermore, in subsp. lubbersii, the leaf surface lacks the hook-shaped cells that are always present in subsp. subnuda (Gerbaulet 1992). However, vegetative morphological characters often used in Portulacaceae as diagnostic are known to be affected by habitat factors. For example, the taxonomic value of the bristle length has been questioned by Burgoyne (1999), as this characteristic seems to be season-related in subsp. subnuda. Burgoyne (1999) recorded the seasonal change in indumentum (covering of hairs) in this taxon, noting that the bristles that protrude, and together with the tomentum (felt-like covering of hairs), cover the leaves during the dormant season, are inconspicuous during the growing season. New leaf growth shows only a sparse covering of fuzz, instead of the typical white, woolly, felt-like tomentum seen in the previous season (Burgoyne 1999). This had been recorded in other species of Anacampseros, where hairs serve as protection against the sun, a means to trap moisture and to ward off insects (see for instance Van Jaarsveld 1987 and Williamson 1994). The presence of the hair envelope occurs when moisture is scarce, depending on the geographical occurrence of the species, in summer (in winter-rainfall areas) or winter (in summer-rainfall areas). In Anacampseros, when sterile material is propagated until flowering, the new growth is often different from that of plants in their natural habitat (Smith et al. 1993).
During the midsummer season—December of 2006—attention was drawn to a colony of Anacampseros subnuda subsp. subnuda in the southeastern region of the North West Province, which proved to consist of two taxa that occur sympatrically. The first, A. subnuda subsp. subnuda (Figure 1), is common at the site, and easily identifiable through its small, angular leaves and the white hairs that closely envelop them. In this population these hairs appeared to be conspicuous even during the wet summer season. On closer inspection individuals of the second taxon turned out to lack the tomentum covering the leaves and to have smooth, shiny green and nearly globular leaves. The long, sparse axillary hairs appear mostly frilly and spreading, forming a tangled mass at the top of the stem, and are present in the new growth (Figure 2). The flowers are quite large and a rosy pink color (Figure 3). This species was described as A. decapitata.
1
Anacampseros subnuda subsp. subnuda growing in a quartz field at Maanhaarrand, Magaliesberg. The leaves are enveloped by short, fuzzy hairs. Photo by G.F. Smith.
2
The recently described species, Anacampseros decapitata, grows sympatrically with A. subnuda subsp. subnuda at Maanhaarrand. The shiny green leaves lack a cover of hairs, but the axillary hairs are quite long and conspicuous. Photo by G.F. Smith.
In addition to the consistent vegetative morphological differences, A. decapitata also has a vegetative dispersal mechanism that has not yet been observed in the similar-looking A. subnuda subsp. subnuda, nor the genus as a whole, as far as I know. The terminal part of the stem becomes easily severed, especially during times of environmental stress, and a rounded segment is blown along the ground, looking like a blackberry or miniature tumbleweed that will root where it becomes lodged in places suitable for colonization. The leaves in these propagules become shriveled and reddish, and are surrounded by numerous, long, spreading, protective hairs. These propagules were observed in summer, the rainy season. Like the other taxa of Anacampseros (Bleck 1984; Williamson 1994), this new taxon is self-fertile. The flowers are ephemeral though, opening for a very short period of time only.
Description of Anacampseros decapitata
Plants small, low-growing, perennial, succulent herbs, not exceeding 70 mm in height; plant bodies single, or more commonly, branched from the base or slightly higher up to form small, dense, tufted, mat-like clumps. Branches herbaceous, densely packed with leaves, up to 45 mm long; 4–5 mm in diameter; upper fifth of leafy tips often abscising to form rounded, mobile propagules. Roots rhizomatous, thickened, with numerous fibrous roots. Leaves persistent, closely adpressed, arranged into tightly packed, elongated rosettes; 5–6 mm long, ± 3 mm wide, 3 mm thick, obovoid-cuneate with a ± rounded upper surface and rounded apex, dark green to purplish brown, fleshy, smooth, glabrous; axils with white, curly, robust hairs up to 15 mm long and 1 mm wide. Inflorescence a pseudo-monochasium, 20–40 mm tall, pedicels 2–4 mm long. Bracts lanceolate, 6–8 mm long, ca. 3 mm broad, white, hyaline. Flowers 2–6, ca. 15 mm in diameter, strongly self-fertile; sepals 2, ca. 8 mm long, ca. 3 mm broad, lanceolate, acute; petals 5, ca. 8 mm long, ca. 4 mm broad, ovate, slightly dished, dark pink; stamens ca. 25, ca. 4 mm tall, anthers ovoid, yellow. Style slightly longer than the stamens, stigma tripartite ca. 2 mm long, white. Fruit ca. 6 mm long, ovoid to cylindrical. Seed 5–7 mm long, reniform-beaked, colliculate. Chromosome number: unknown.
Distribution range
Anacampseros decapitata has thus far only been recorded from South Africa's North West Province on the Magaliesberg, near Breedt's Nek, at an altitude of about 1654 m above sea level. The savanna vegetation (Mucina and Rutherford 2006) at this locality is rich in succulents. Common species include the miniature mesembs Frithia pulchra N.E.Br. and Khadia acutipetala (N.E.Br.) N.E.Br., the crassuloid species Adromischus umbraticola C.A.Sm. subsp. umbraticola, Crassula setulosa Harv. var. setulosa and Kalanchoe thyrsiflora Harv., the milkweed Euphorbia davyi N.E.Br., and Anacampseros subnuda subsp. subnuda. Other species include numerous grasses, such as Themeda triandra Forsk., and the small, shrubby tree Englerophytum magaliesmontanum (Sond.) T.D.Penn. The species only occurs in a very specific habitat consisting of shallow sandy soils overlying sheets of rock amongst moss or gravel, as well as at the base of grass tussocks and sometimes under low vegetation. Anacampseros subnuda also occurs there in a wider variety of habitats but the two species seldom grow very close to each other (Andrew Hankey, Walter Sisulu National Botanical Garden, pers. comm.).
Conservation status
Anacampseros decapitata is sparsely distributed among grasses and in gravel patches. The type locality seems to be a popular recreational area for outdoor enthusiasts who frequent the area with 4 × 4 off-road vehicles. The species is therefore vulnerable to the effect of human activities in that locality.
Acknowledgements
Mr Andrew Hankey, specialist horticulturist and assistant curator at the Walter Sisulu National Botanical Garden of the South African National Biodiversity Institute, is thanked for drawing attention to Anacampseros decapitata.
