Drosanthemum longipes (L.Bolus) H.E.K.Hartmann
Common names: Biedouw drosanthemum (Eng.); biedouw-rankvygie (Afr.)
A remarkable, summer dormant, scrambling, leaf succulent, with magenta-pink flowers in winter, re-sprouting annually in autumn, producing many stems from a turnip-shaped tuber. The leaves are flat and unique for the genus Drosanthemum. It grows in Succulent Karoo, in the Western Cape.
Drosanthemum longipes has ascending, spreading, scandent branches and grows to about 600 mm tall, making use of the support of the nurse shrub it is growing under. The subterranean turnip-shaped tuber is 40–80 mm in diameter and 100–150 mm long, the upper part rounded to flat with several (7–30) ascending to ascending spreading, angular to terete branches, up to 600 mm long. The bark of the tuber is longitudinally fissured, fibrous and yellowish brown; the roots tapering and dividing below.
The lower stems is about 8 mm in diameter with peeling brownish bark; the upper stems 1–4 mm in diameter; the internodes 23–50 mm apart, greenish and covered in papillae, 6-ribbed in younger growth. The leaves are sessile, light green, softly succulent, in opposite pairs (decussate), ascending spreading, linear-oblanceolate, channelled, flattened, 15–35 × 3–10 mm, often crowded at the branch ends (in groups of up to 6 leaves); upper and lower surface densely covered in papillae (dome-shaped translucent bladder cells); the margin and main lower protruding vein with slightly larger, transparent papilla. The leaf tip is blunt (obtuse) to subacute.
The flowers are solitary, 25–50 mm in diameter, on long pedicles 55–73 × 1–2 mm, at first purplish pink, turning brownish. The fruit (receptacle) is top-shaped, 8 mm in diameter and 5 mm deep, with 5 raised ridges at the top, surrounded by a ring of nectar glands. The stigmas (female portion) are 5-pointed, spreading 3 mm long, purplish, each divided into 1.5 mm pointed lobes, becoming whitish when receptive. The calyx lobes are green, 5 × 5, obtuse, each with a terete point 4.5 × 1 mm, each of the 3 inner with membranous margin turning blackish; petals purplish pink, linear. Capsule 7–10 mm in diameter, hygrochastical, covering membranes absent. Seed globose, 1.0–1.2 mm in diameter and with a protruding rounded point, with minute papillae.
Although Drosanthemum longipes is restricted to a small area in the semi-arid region near Biedouw Valley in the Western Cape, South Africa, it is fairly common and not threatened, and, therefore, assessed as Least Concern (LC) in the Red List of South African plants.
Distribution and habitat
Drosanthemum longipes grows on the south to west-facing upper eastern slopes of the Biedouw Valley, close to the top of Uitkyk Pass, at about 500–700 m above sea level. It grows with a climbing habit (scandent) among various shrubs, becoming conspicuous in winter (August), when its bright magenta-pink flowers appear. This region is semi-arid with frontal rainfall of about 250–300 mm per annum in winter, from May to September, which is the growing season for D. longipes, and long, dry summer months, when the temperature rises well above 30ºC. Winter is cooler with rain received during cold fronts. When frost occurs it is light.
The geology consists of Bokkeveld Shale rocks giving rise to clay-loam soils.
It grows in the Succulent Karoo Biome. Plants were observed mainly on the richer shale soils in succulent karoo vegetation named as Agter–Sederberg Shrubland of the Rainshadow Valley Karoo Bioregion (Mucina 2006), but also to a lesser extent on the mineral-poor sandstone soil in the adjacent Sederberg Sandstone Fynbos vegetation (Sandstone Fynbos), growing below shrubs, the branches scandent and extended above the nurse plant canopy. Other associated succulent karoo species sharing its habitat include Tylecodon ventricosus, a form with large leaves, as well as a species of Antimima.
Derivation of name and historical aspects
The genus Drosanthemum was established by Schwantes in 1927. The name Drosanthemum is derived from the Latin droso, meaning ‘dew’ for the glittering dew-like bladder cells, and anthemon, meaning ‘flower’ giving rise to the name Drosanthemum or ‘dew flower’ (Clarke & Charters 2016). The specific epithet longipes means ‘long stalked’ and is derived from the Latin longus, meaning ‘long’ and pes, ‘foot’, pertaining to the long floral stalks.
The mesembs are a diverse group of succulents almost 90% confined to South Africa and especially in the winter rainfall region in the south and west. Drosanthemum belongs to the subfamily Ruschioideae and consist of a group of 130 species, mostly small, much-branched, succulent-leaved shrublets, ranging from the flat growing Drosanthemum hispidum to the more than 2 m tall D. anemophilum (Van Jaarsveld & Hammer 2004).
Drosanthemum longipes was first named by the German explorer Rudolph Schlechter as Mesembryanthemum schuhmannianum, but was invalidly published. The plant was renamed as Delosperma longipes by Louisa Bolus in 1929, in her notes on Mesembryanthemum and allied genera, on the ground of the fruiting capsules which lack covering membranes. It was transferred to the genus Drosanthemum by Heidi Hartmann in 2001. Hartmann divided Drosanthemum into 10 sugbenera and D. longipes was placed under her subgenus Decidua (5 species), based mainly on vegetative features, such as summer deciduousness and the internodes of the species widening towards their apical ends. The floral and fruiting characteristics are, however, remarkably diverse in these 6 species (D. anemophilum, D. deciduum, D. decumbens, D. inornatum, D. longipes, D. pauper). Drosanthemum longipes is very distinct from other members of Decidua Hartmann, and immediately separated by the distinct turnip-shaped caudex, flat to rounded at the top, with several branches rising from the top and the flattened leaves, which is not very typical of Drosanthemum.
The distinctly flattened leaves are an adaptation to their shady habitat, consisting of shrubs such as Asparagus capensis, Searsia incisa, a species of Pteronia, Eriocephalus and Zygophyllum meyeri. Another scandent geophyte sharing its habitat, is Melasphaerula ramosa (Iridaceae), which has a scandent inflorescence. The leaves of Drosanthemum longipes are hidden or just exposed within the nurse shrubs canopy, but the extended flowers protrude, making it visible to the pollinators. D. longipes when exposed to full sun, will also grow extended stems, but much shorter. The plant resprouts after disturbances, such as fire or grazing.
The fruiting capsules are hydrochastical (opening only with moisture and closing again when drying out). The expanding keels push open the cell lids and the seeds, which are without covering membranes, are splashed out by rainwater and the seed dispersed locally around the mother plant by falling rain drops. This ensures that it stays within the safe habitat.
The plant flowers profusely during the month of August (southern hemisphere). The open flowers are pollinated by bees, the flowers protandric, which means first the stamens ripen, allowing bees access to the pollen. Only after the stamens bend back, do the stigmas reach maturity, thus preventing self-pollination.
Occasionally propagated and cultivated and used as an ornamental caudex plant.
Growing Drosanthemum longipes
The Biedouw drosanthemum is only grown occasionally by specialist growers of succulent plants. The plant is slow growing and long-lived and when planted with the tuber partially exposed, it makes a peculiar and attractive caudiciform plant. A support structure should be erected to support the ascending branches. Best for containers grown in a greenhouse or windowsill where it can be protected from excessive rain or low temperatures. It is well-suited for dry Succulent Karoo gardens (Van Jaarsveld 2010).
Propagate from seed. Crush the dried fruiting capsules and sow in autumn in shallow trays. Cover with a thin layer of sand (1–2 mm thick) and keep moist. Germination should be within 3 weeks (when seed is viable). Plant out when large enough to handle.
- Clarke, H. & Charters, M. 2016. The illustrated dictionary of southern African plant names. Flora & Fauna Publications Trust, Jacana, Johannesburg.
- Hartmann, H.E.K. 1991. Mesembryanthema. Systematics, biology and evolution of some South African taxa. Contributions from the Bolus Herbarium. No. 13: 75–157.
- Hartmann, H.E.K. 2000. The capsules of Drosanthemum Schwantes (Ruschioideae, Aizoaceae). Bradleya 18: 75–112.
- Hartmann, H. 2001. Aizoaceae A-E. In Eggli, U. & Hartmann, H.E.K. (eds.) Handbook of succulent plants. Springer, Heidelberg, New York
- Hartmann, H.E.K. 2007. Studies in Aizoaceae: eight new subgenera in Drosanthemum Schwantes. Bradleya 25: 145–176.
- Hartmann, H.E.K. 2014. Two new subgenera and one new species in the Genus Drosanthemum. Bradleya 32: 50–63.
- Mucina, L. & Rutherford, M.C. (eds) 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria.
- Van Jaarsveld, E.J. 2010. Waterwise gardening in South Africa and Namibia. Struik, Cape Town.
- Van Jaarsveld, E.J. & Hammer, S. 2004. An unusual new species of Drosanthemum from Rooinek Pass in South Africa’s Western Cape. Cactus & Succulent Journal (US) 76,3: 202–204.
Ernst van Jaarsveld
Kirstenbosch National Botanical Garden (Retired)
Extraordinary senior lecturer and researcher, Department of Biodiversity and Conservation, University of the W. Cape.
Plant Type: Scrambler, Shrub, Succulent
SA Distribution: Western Cape
Soil type: Loam
Flowering season: Winter
PH: Alkaline, Neutral
Flower colour: Pink
Aspect: Full Sun, Morning Sun (Semi Shade), Afternoon Sun (Semi Shade)
Gardening skill: Average