Bonatea speciosa, a terrestrial orchid, is admired for its delicate, somewhat bizarre, green and white flowers. It is also comparatively easy to grow both in pots and in flowerbeds in the garden which has added to its popularity.
The plants are deciduous and measure mostly about 0.4-0.6 m in height. At the beginning of the dormant season, the above-ground parts dry off completely, and the plants perennate with their elongated storage tubers. In the growing season, a few dark green and broadly lanceolate leaves are borne along the stem. The inflorescences comprise few to many medium-sized to large green and white flowers. They are very complicated in shape and look somewhat spider-like. The three sepals are unlobed and measure up to 25 mm in length. As also in many species of the closely related genus Habenaria (in which Bonatea was included in the past), the petals are deeply two-lobed, and the three-lobed lip is spurred. The single, erect anther has two long, thin anther canals which are attached to two equally long, thin rostellum (part of the stigma) portions which project forwards. The two stigmas are also long and thin and project forwards.
Bonatea speciosa is fairly common in nature and was classified as LR-lc (= Lower Risk - Least Concern) in a recent assessment of the conservation status of the species (Golding 2002).
Distribution and Habitat
The species is widespread in the southern and eastern parts of South Africa and Zimbabwe where it grows in coastal shrub, on forest margins and sometimes also in savanna up to about 1 200 m. A variety antennifera (Rolfe) Sommerv. was described in comparatively arid areas in the northern provinces of South Africa, in Botswana, Zimbabwe and Mozambique (Linder & Kurzweil 1999); it is sometimes recognized as a separate species (Rolfe 1912-1913; La Croix & Cribb 1995).
Derivation of name and historical aspects
Bonatea was described by the German botanist Carl Ludwig Willdenow in 1805, and named after Guiseppe Bonato, who was professor of botany at Padua in Italy. Currently about 20 species are known in the genus, all of them occurring in mainland Africa with one species ranging into Yemen. Bonatea was at times included in the genus Habenaria with which it shares most of its characters (Kurzweil & Weber 1992). Bonatea differs from Habenaria in the basal fusion of the lateral sepals, anterior petal lobes, lip and stigma processes; the presence of a tooth-like structure in the spur-mouth; and the tall and hood-like central rostellum lobe. The species B. speciosa is one of the more widespread members of the genus, and its species name alludes to the attractive flowers: speciosa means beautiful.
Bonatea speciosa is one of the few African Orchidaceae-Habenariinae where the pollination has been studied in detail (Johnson & Liltved 1997). At night, the strongly evening scented flowers attract hawkmoths which act as the pollinators of the orchid. The pollinaria are exceptionally large, measuring about 20 mm in length, and become attached to the hawkmoths' eyes.
Uses and cultural aspects
As in most orchids, there are no major known uses of Bonatea speciosa, but there is considerable horticultural potential for this species.
Growing Bonatea speciosa
It is essential to grow Bonatea speciosa in a well-drained growing medium as water-logged soil leads to the rapid rotting of the plants. The plants can either be grown in garden beds or in pots. Pot culture obviously has the advantage that the plants can be moved (e.g. to take flowering specimens indoors). Plants cultivated in garden beds require a shady or semi-shady spot.
The growing medium should consist of equal parts of fibrous peat, loam, coarse sand and fine bark, to which drainage chips should be added. If grown in pots, a layer of drainage material at the bottom is required. It is generally advisable to follow the rainfall pattern in the natural habitat where your particular plant originates (the species generally occurs in both the winter and summer rainfall regions). The soil should be kept fairly dry in the dormant season, but should also not dry out completely. Unlike most orchids, bonateas do not like high humidity (La Croix & La Croix 1997). While winter temperatures can drop to 5 degrees Celsius, summer temperatures should not exceed 30 (Wodrich & Vogelpoel 1999).
As plants of Bonatea speciosa do not form dense clumps that can be divided, propagation from seed is the only viable alternative. However, this form of propagation is rather complicated in orchids, and requires the facilities of a modern chemical laboratory. It is necessary to follow an in vitro method that is commonly known as 'flasking'. Sterile working conditions as well as chemicals to mix the jelly-like growing medium with all its nutrients are essential.
The most serious cultivation problem is rotting of the tubers, stems or roots due to over-watering. For this reason it is a good idea to avoid wetting the leaves and new shoots altogether.
For more about SA orchids and growing them, see the Orchids pages on this site.
References and further reading
- Golding, J.S. (ed.). 2002. Southern African plant Red Data Lists. Southern African Botanical Diversity Network Report No. 14. SABONET, Pretoria.
- Johnson, S.D. & Liltved, W.R. 1997. Hawkmoth pollination of Bonatea speciosa (Orchidaceae) in a South African coastal forest. Nordic Journal of Botany 17: 5-10.
- Kurzweil, H. & Weber, A. 1992. Floral morphology of southern African Orchideae. II. Habenariinae. Nordic Journal of Botany 12: 39-61.
- La Croix, I.F. & Cribb, P.J. 1995. Orchidaceae. In G.V. Pope, Flora zambesiaca. Flora Zambesiaca Managing Committee, London.
- La Croix, I.F. & La Croix, E. 1997. African orchids in the wild and in cultivation. Timber Press, Portland, Oregon.
- Linder, H.P. & Kurzweil, H. 1999. Orchids of southern Africa. Balkema, Rotterdam.
- Rolfe, R.A. 1912-1913. Orchideae. In W.T. Thiselton-Dyer, Flora capensis 5, 3: 3-313. Reeve, London.
- Wodrich, K. 1997. Growing South African indigenous orchids. Balkema, Rotterdam.
- Wodrich, K. & Vogelpoel, L. 1999. Cultivation. In H.P. Linder & H. Kurzweil, Orchids of southern Africa. Balkema, Rotterdam.
Compton Herbarium, Kirstenbosch Research Centre