Piaranthus
Piaranthus is a genus of small, low-growing stapeliad succulents in the milkweed family (Apocynaceae), native to the drier parts of southern Africa. The plants form spreading clumps of soft, knobbly, leafless stems and carry modestly sized, star-shaped flowers that are frequently spotted or finely mottled. Like their better-known relatives Stapelia and Huernia, they belong to the group of stem succulents affectionately known to growers as the "carrion flowers", though Piaranthus blooms are generally small and only mildly scented.
Description
Piaranthus plants are among the smaller stapeliads. They form low, sprawling mats of short, fleshy stems that branch freely from the base and creep along the soil surface. The stems are typically only a few centimetres long, angled or nearly cylindrical, and covered in blunt, rounded tubercles that give them a soft, knobbly texture. Colour ranges from grey-green to bronze or purplish, depending on light and stress. The plants are leafless, with photosynthesis carried out by the stems themselves — a classic adaptation to dry, sunny habitats.
The flowers are the main attraction. Borne singly or in small clusters near the stem tips, they are star-shaped with five spreading lobes and usually only a couple of centimetres across. Petal surfaces are often cream, yellow or brownish and marked with fine spots, bars or a wrinkled texture, and many carry a fringe of small hairs. As with other stapeliads the flowers are fly-pollinated, but the scent in Piaranthus is typically faint compared with the powerful odour of larger genera.
Distribution
The genus is centred in southern Africa, with most species occurring in South Africa and Namibia. Plants grow in arid and semi-arid habitats — rocky flats, gravelly slopes and the shade of small shrubs — where they are often tucked out of sight among stones and low vegetation. Their sprawling, well-camouflaged stems and shallow roots suit shallow, fast-draining pockets of mineral soil.
Notable species
- Piaranthus punctatus — a widespread, variable species with spotted flowers, often grown as a beginner's introduction to the genus.
- Piaranthus geminatus — noted for its neat clumping habit and star flowers marked with fine bars or spots.
- Piaranthus cornutus — distinguished by the shape and markings of its small blooms.
- Piaranthus framesii — a compact plant popular in specialist collections, now often treated as a variety of P. punctatus.
Species boundaries in Piaranthus are notoriously fluid, and plants have been shuffled between names over the years; expect some overlap and synonymy between the forms offered in cultivation.
Cultivation
Piaranthus are rewarding, undemanding little plants that do well in the same conditions as most stapeliads. Grow them in a very free-draining, mostly mineral mix in a wide, shallow pot that suits their creeping habit. Give bright light with some shade from the fiercest afternoon sun — a little shade keeps the stems plump and green, while too much sun can scorch or bronze them and too little causes weak, drawn growth.
Water moderately through the warm growing season, always letting the mix dry out between waterings, and keep the plants dry and cool through winter to prevent rot. As with all stem succulents, overwatering — especially in cold or stagnant conditions — is the quickest way to lose a plant. See Watering and Repotting for general technique, and Pests and diseases for the usual stapeliad troubles (mealybugs in the stem crevices and rot at the base being the most common).
Propagation
Piaranthus are very easily increased from stem cuttings. Detach a segment, let the cut surface dry and callus for a few days, then lay or set it on a dry mineral mix; roots form readily where the stem contacts the soil. Because the plants clump and creep naturally, division of an established mat is just as simple. Seed is also possible where fresh, fly-pollinated pods are available, but cuttings are so quick and reliable that most growers rarely bother. See Propagation — cuttings and Propagation — seed for details.
Hobby and cultivar notes
Piaranthus is a favourite among stapeliad enthusiasts precisely because it is small, floriferous and forgiving — a windowsill collection of several forms takes up little room. Little formal cultivar selection has been done; interest centres instead on the natural variation between species and localities, and on growing a range of the charmingly spotted flowers. The plants are frequently traded and grown alongside related genera such as Huernia, Stapelia and Duvalia, with which they share care and, occasionally, hybridise in collections.
See also
- Stapeliad — the broader group of stem-succulent "carrion flowers"
- Huernia · Stapelia · Duvalia — related stapeliad genera
- Soil and potting mix · Watering · Propagation — cuttings · Pests and diseases