Gasteria armstrongii is a dwarf aloe-like, succulent-leaved stone plant, endemic to the Renosterveld flats between Jeffreys Bay and the Gamtoos River of the Eastern Cape Province. It thrives in cultivation.
Plants without a stem (acaulescent), and with leaves (up to 3 pairs) remaining flat on the ground, one above the other in two opposite rows (distichous), solitary or proliferating from the base to form small clusters. Roots succulent, slightly dilating towards the middle. Leaves 30–60 mm long, 23–35 mm broad at the base, firm, triangular to triangular-lorate (lorate = strap-shaped), the inner ascending-spreading, the outer spreading; the upper surface channelled towards the base; lower surface somewhat convex without a keel; both surfaces dark green, with dense to sparse whitish tubercles arranged in irregular transverse bands; the leaf tip is acute, bearing a short sharp point (mucro); the leaf margin is horny, acute and entire. Inflorescence an ascending solitary raceme, 400–500 mm long. Pedicel 5–6 mm long. The perianth is about 20–24 mm long, reddish-pink, the base swollen for more than half its length. Stamens 20–24 mm long, anthers 2 mm long, oblong, included or slightly protruding, the style about 18–24 mm long, exceeding the anthers at the end of the flowering period. The fruiting capsule 20–25 mm long, 6–8 mm in diameter. Seeds about 3–4 mm long, black, flattish.
||Gasteria armstrongii flowering in cultivation
Flowering period: January–February (midsummer).
Gasteria armstrongii is related to G. nitida which is a much larger grassland plant with a smooth leaf surface. The former is immediately recognized by its spreading leaves in two opposite rows of tuberculate, triangular to triangular-lorate, spreading leaves and solitary racemes. G. nitida is a much larger plant bearing smooth triangular-lanceolate leaves in a rosette and a branched inflorescence. G. armstrongii is an attractive dwarf species, a true stone plant resembling its pebbly background.
Gasteria armstrongii is vulnerable, occurring in a popular farming region. It is also only known from a few sites along the Gamtoos River in the Eastern Cape. Although it is well camouflaged and difficult to find, it is threatened by collectors and ploughing. Plants grow on a flat terrain in Renosterveld vegetation. The plant has been well established in cultivation (ex situ preservation) and is grown by succulent plant enthusiasts all over the world.
Distribution and habitat
Gasteria armstrongii grows in a fynbos community known as Humansdorp Shale Renosterveld vegetation (Mucina & Rutherford 2006). Its habitat is a flat to hilly terrain rich in pebbles among which G. armstrongii is difficult to detect. The plants grow in full sun or are partially covered by small shrubs. Plants growing with G. armstrongii include Boophone disticha, Pachypodium bispinosum, Bergeranthus glenensis, Euphorbia gorgonis, Freesia alba and Crassula tetragona subsp. acutifolia.
||Gasteria armstrongii growing in its natural habitat in Renosterveld vegetation (near the Gamtoos River, E. Cape)
The coastal climate is mild in both summer and winter. Average rainfall is 400–500 mm per year and occurs in summer and winter, but there is a tendency to winter dryness. The average annual daily maximum temperature is about 22°C and the average daily minimum about 12°C.
Derivation of name and historical aspects
Gasteria armstrongii was named by the botanist Selmar Schönland (1860–1940), director of the Albany Museum in Grahamstown. The plant commemorates William Armstrong a plant enthusiast from Port Elizabeth. He is also commemorated in Freesia armstrongii (Gunn & Codd 1981).
Gasteria armstrongii grows on pebbly soil, merging with the background. The dark greenish tuberculate leaves are the same colour as the pebbles and are difficult to detect when the plant is not in flower. During drought the leaves become dark reddish-brown tanned and may retract until only the upper leaf surface shows above the soil surface. Dust and leaves often get blown over the plants so that they blend in even more effectively with the natural surroundings. The plant is thus rarely spotted and escapes predation. It is pollinated by sunbirds. Seeds ripen during summer, coinciding with the rainy season. The capsules, when ripe, are held in an erect position. Seeds are released by strong gusts of wind and are thus wind-dispersed. Like in many other Gasteria species its leaves are brittle and will proliferate when fallen on the ground after having been detached by herbivores or other agents. The succulent leaves and roots enable the plant to cope with the dry season and general dry conditions.
Uses and cultural aspects
Apart from its horticultural use, the plants are not known to be used medicinally or otherwise.
||Gasteria armstrongii in habitat on coastal flats near the Gamtoos River.
Note how well the plants are camouflaged.
Growing Gasteria armstrongii
Gasteria armstrongii thrives in cultivation and does best as a pot plant or grown in miniature rock gardens. It is a slow grower. It can also be grown out-of-doors, but is best cultivated in dry Mediterranean-type gardens where frost is not too severe. Although it can be grown in full sun, plants prefer some slight shade, and in hot climates should therefore be protected from full sun. Plants should reach flowering size in about 3 years.
Easily propagated from seed, by division or from leaf cuttings. It is best to apply a fungicide when growing from seed. Sow seed during spring or summer in a warm, shady position in a sandy slightly acidic soil and keep moist. Cover with a thin layer of sand and keep moist. Germination is usually within 3 weeks. Seedlings grow slowly and are best planted out about a year after sowing. Propagation from leaf cuttings is best undertaken in spring. Allow the leaf cutting to form a heel by placing it on a dry window sill for a week or three. Cuttings are best rooted in clean sand. Once rooted, plants can be planted into individual containers. Plants react well to organic feeding (compost or any other liquid fertilizer). G. armstrongii is best watered throughout the year, but sparingly in winter.
References and suggested reading
- Gunn, M. & Codd, L.E. 1981. Botanical exploration of southern Africa. Balkema, Cape Town.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. 1994. Gasterias of South Africa. Fernwood Press, Cape Town.
- Van Jaarsveld, E.J. 2007. The genus Gasteria, a synoptic review. Aloe 44: 4: 84–103.
Ernst van Jaarsveld
Kirstenbosch National Botanical Garden