Bulbine rupicola
Introduction
A dwarf cliff-hugger, with numerous dwarf rosettes of dull green, rounded, soft, succulent leaves from cliffs in the southwestern corner of the Eastern Cape. It flowers in spring when the solitary inflorescence appears, bearing yellow flowers. Best grown in containers.
Fig. 1. The dwarf cliff bulbine (Bulbine rupicola) in habitat on a sheer cliff at Keurkloof, near the Kouga River.
Description
Description
Bulbine rupicola plants are dwarf-sized, rosulate, forming dense clusters, up to 80 mm in diameter, containing many heads, growing from oblong to oblong-ovoid tubers (yellow flesh), but only one to two heads flowering per cluster. The tubers up to 10–12 × 5–12 mm, grey, covered with the fibrous remains of leaves. Roots yellowish, terete, up to 1 mm in diameter. Leaves up to 3–7, in a rosette, ascending, linear to linear-lanceolate, 15–30 × 6–10 mm, triangular-lanceolate to subterete, green, with soft texture, becoming reddish under dry conditions; upper side flat to convex, becoming channelled during the dry season, cymbiform below, green and slightly glaucous and faintly translucent, striate, covered with powdery bloom; margin entire or finely toothed; apex acute-mucronate. Inflorescence 50–120 mm long, 3–8-flowered, in distal quarter; peduncle 1 mm in diameter at base, terete, reddish; bracts deltoid-acuminate, 1.5 × 1.0 mm, clasping; pedicels 7 mm long. Perianth stellate, becoming reflexed, slightly drooping to drooping, about 8–14 mm in diameter; tepals yellow with darker brownish central stripe in each tepal, outer tepals obovate-elliptic, 7 × 3 mm, channelled, inner tepals ovate to ovate-elliptic, 6 × 4 mm, obtuse. Stamens up to 5 mm long, bearded. Ovary oblong-globose, up to 1.2 × 2.0 mm. Fruit a rounded capsule, up to 2.5–3.0 mm in diameter. Seeds angular, black, 2 × 1 mm, minutely wrinkled.
Flowering is in early to midsummer, from November to January. Seeds are dispersed by wind in summer.
Fig. 2. The Kouga River, cliffs on both sides, habitat of the dwarf cliff bulbine (Bulbine rupicola), and a close-up of Bulbine rupicola in habitat on cliffs at Keurkloof.
Conservation Status
Status
Bulbine rupicola is widespread in the southeastern Eastern Cape and is also well protected by its difficult to reach, cliff habitat and its distribution falls within a greater conservation region. Consequently it is assessed as Least Concern (LC) the Red List of South African plants.
Fig. 3. A young cluster of the dwarf cliff bulbine (Bulbine rupicola) at Keurkloof. Note the moss in the background.
Distribution and habitat
Distribution description
Bulbine rupicola is widely spread, usually confined to quarzitic sandstone cliffs, from the Kouga Mountains (Hankey District) in the south, to near Klipplaat northeast of Willowmore in the north, also including the eastern end of the Swartberg where it is confined to the narrow kloofs (usually north-south orientation), at an altitude of 500–800 m. The habitat includes cliffs (all aspects). Plants are firmly rooted in crevices, their size often depending on the growing space allowed by the crevice. The plants continue to proliferate and fill the crevices and ledges. Temperature is high in summer (30–35ºC). Winters are cooler but frost is light or absent. Rainfall occurs throughout the year, but with a peak in spring and summer, 300–400 mm per annum (thunder showers or cyclonic winter rain). The associated vegetation consists of Gamtoos Thicket and dry Fynbos at higher altitudes (Mucina et al. 2006). Associated cliff-dwelling plants near Keurkloof, Kouga River include Albuca cremnophila, Crassula cremnophila, C. perfoliata var. minor and C. perforata and Gasteria glauca. At Toorwaterspoort, plants grow with Aloe mitriformis, Cotyledon woodii, Haworthiopsis viscosa, Bijlia sp., Curio ficoides, Crassula capitella subsp. thyrsiflora, C. muscosa, C. orbicularis and C. ovata and Adromischus subdistichus.
The geology within the habitat consists of quarzitic sandstone (light-coloured and smooth-textured), Peninsula Formation (Cape Supergroup). The cliffs have many ledges, crevices and fissures, which are ideal for the establishment of plants.
Fig. 4. Bulbine rupicola cluster in habitat, filling a sloping ledge, during a dry period at Keurkloof, Kouga. The reddish colour of the leaves is caused by anthocyanins, a pigment that lowers the rate of photosynthesis.
Derivation of name and historical aspects
History
Bulbine rupicola was aptly named by Graham Williamson in Bradleya, the magazine of British Cactus & Succulent Society, in 2000. Graham focuses on succulent plants and collected his plants in a kloof northeast of Klipplaat, in the Eastern Cape. The name rupicola is Latin and pertains to its rocky habitat, rupes meaning ‘cliff’ or ‘rock’, and cola meaning ‘dweller’.
Bulbine rupicola is at once distinguished by its very dense growth of dwarf rosettes with soft, fragile, dull-green, semi-translucent, glaucous leaves of which the surface is smooth. Also its dividing nature, forming dense clusters. It belongs to a group of summer-rainfall, broad-leaved Bulbine species. It comes closest to B. retinens and B. cremnophila, both of which are also cliff dwellers. B. retinens is much larger, with a differently shaped tuber, distinctly glaucous, with long, linear leaves and fruit that retains the seed for some time. Both have a prolific nature. B. cremnophila has leaves that curve downwards, and forms small clusters as it does not have the prolific nature of B. rupicola, which has ascending leaves.
Fig. 5. Toorwaterspoort in the Eastern Cape, southwest of Willowmore, habitat of Bulbine rupicola and plants growing on the cliffs.
Ecology
Ecology
Growing in a shallow crevice or on a ledge on a sheer cliff face, demands a plant that can survive periods of drought and competition from other plants. Bulbine rupicola has several advantages that allow it to dominate in its native habitat. The tubers, which store water, and the highly succulent leaves act as a reservoir. During extreme drought, the leaves become channelled and eventually desiccate and the tubers go into dormancy, but will grow leaves again with the onset of rain. Its highly prolific nature (vegetative/asexual propagation) ensures an ability of intense competition of space by pushing out other succulent species growing in the same crevice. Its dense network of roots make it difficult for other succulents to establish. The greyish leaves are covered with a powdery bloom assisting with water conservation and its semi-translucent nature allows efficient light penetration.
Solitary or sparingly branched species of Bulbine, such as B. latifolia, will regularly flower ensuring sufficient seed production. In the case of B. rupicola, much energy is placed in vegetative reproduction and the plant only forms one or two inflorescences. The prolific nature maximises survival and compensates for reduced sexual output (fewer inflorescences, flowers and seeds). This mode of flowering is also observed in, for instance, other succulents such as Gasteria bicolor var. liliputana which produces many heads but only one or two will produce flowers, as opposed to G. excelsa, a solitary plant with a massive inflorescence.
The flowers of Bulbine rupicola are cross-pollinated by insects, the seeds dispersed by wind in late summer or autumn, which is the best time for receiving rain in its habitat. The initial orientation of the flower buds is erect but as the flowers mature, they curve downwards. This sub-pendulous orientation of the perianth renders the flowers more conspicuous in the narrow, shady kloofs, when viewed from below, and is thus an adaptation, maximising visibility for pollination in the vertical cliff environment. The seed germinates when landing on a ledge or crevice, the young seedling rapidly growing and proliferating establishing another cliff-hugging cluster.
Fig. 6. A cluster of the dwarf cliff bulbine (Bulbine rupicola) in habitat, Kouga.
Uses
Use
No medicinal or cultural uses have been recorded.
Fig. 7. The dwarf cliff bulbine (Bulbine rupicola) growing in a container. Note the faintly striate leaves.
Growing Bulbine rupicola
Grow
Bulbine rupicola is easily grown from seed or division. It is best grown as a pot plant in partial shade and kept in small containers, simulating the small crevices of the cliff environment. The soil should be sandy, well drained and slightly acid, as is found in its natural habitat. They will react well to any fertiliser but organic fertilisers, such as well broken down compost is best, with ample feeding throughout the year. Outside its habitat, it is best grown under controlled conditions in a greenhouse. As a pot plant, it can be grown on a balcony or windowsill.
In its habitat at the Kouga and the Willowmore District, rain can be expected any time of the year but more so from spring to autumn. Best to water well in summer and keep dry in winter. The plant is also frost-sensitive and should be protected in winter. The young plants start solitary, soon dividing forming small, dense clusters.
Divide plants at any time of the year, and plant in a shallow tray in a sandy mixture (such as peat, sand and polystyrene) and keep moist. Rooting is within 3 weeks and once well rooted, transfer to individual containers. Place container in a shady position but with full light. The south side of a building is ideal.
Sow seed in spring, summer or autumn in a sandy medium. First moisten the substrate with a fine rose. Cover the seed lightly with a thin layer of sand. Keep moist and in a shady position. Germination is usually within 3 weeks and the young seedlings are relatively fast growing. Transplant seedlings to individual containers once large enough to handle.
Plants are relatively disease free but a leaf ring fungus, slugs and snails can sometimes be a problem.
References
- 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. & Forster, P.I. 2001. Bulbine. In U. Eggli, Sukkulenten Lexicon (Band 1). Einkeimblattrige Pflanzen (Monocotyledonen). Ulmer, Stuttgart.
- Van Jaarsveld, E.J. & Potter, L. 2005. Bulbine rupicola G.Will. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2021/04/16
- Van Jaarsveld, E.J. & Van Wyk, A.E. 2003. Four new cliff-dwelling Bulbine taxa (Asphodelaceae) from the Eastern and Western Cape. Aloe 40(1): 4–7.
- Williamson, G. 2000. Four new, succulent Bulbine species (Asphodelaceae) from the Western and Eastern Cape Provinces of the Republic of South Africa. Bradleya 18: 31–40.
Credits
Ernst van Jaarsveld
Kirstenbosch National Botanical Garden (Retired 2015)
Babylonstoren Farm
Extraordinary senior lecturer and researcher,
Department of Biodiversity and Conservation, University of the Western Cape
April 2021
Plant Attributes:
Plant Type: Succulent
SA Distribution: Eastern Cape
Soil type: Sandy
Flowering season: Early Summer
PH: Acid
Flower colour: Yellow
Aspect: Morning Sun (Semi Shade), Afternoon Sun (Semi Shade)
Gardening skill: Easy
Special Features:
Good potplant
Horticultural zones
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