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Group of Disa Orchids in the wild

The Collection of African orchids in cultivation at Kew is probably the best in the world from that continent. At least 400 species are grown, with representatives from 60 of the 100 genera that have been recorded. Orchids are grown from most African countries, but the collection is most rich in species from Malawi, Kenya, Tanzania, South Africa and Gabon, partly because Kew has had very generous contacts in these countries and partly because plants from these countries have been more intensively researched in recent years. They provided much useful material for the account of the Orchidaceae for the Flora of Tropical East Africa, which was completed in 1989. As in other parts of the world, terrestrial species are more frequent in the temperate climatic areas and epiphytes more common in the equatorial zones. Thus in South Africa, about one-tenth of the orchids are epiphytes whereas in Kenya and Zaire half of the orchid species are epiphytic.

Most of the African terrestrial orchids in the Kew collection come from South Africa. The genus Disa, the most well known, has been in cultivation at Kew intermittently since early in the 19th century; Disa cornuta was recorded in the second edition of Aiton's Hortus Kewensis. By the end of the century several other species were grown and an artificial hybrid bred at Kew, Disa Kewensis (D. uniflora X D. tripetaloides) was registered in 1893. Disas have great potential for display as they flower during the summer months when many other orchids are in vegetative growth. They produce tall racemes of many brightly coloured flowers, each rather distinctive and eye catching with its enlarged dorsal sepal and two wide lateral sepals.

Disa kewensis

In their natural habitats many of the 200 or so Disa species grow near streams or in damp grasslands, though they have a wide altitudinal range from sea level to at least 3000 m. Many growers in England have found that disas are difficult to keep in cultivation, but at Kew it has been shown that frequent repotting is the vital key for success. The plants are grown in a mixture of equal parts of fibrous peat and perlite, repotted after flowering and kept comparatively dry for several weeks so that they get a short rest. During the winter they grow actively and, with a minimum night temperature of 11º C (52º F), need watering at least twice each week. In the spring, water can be given daily to maintain the fat clumps of fresh green foliage. Foliar feeding ensures the development of good flower spikes. It seems to be important, however, that the plants do not stand in still water and that the compost does not become stagnant; frequent repotting prevents this.

Disa uniflora has flower spikes up to 50 cm tall and may bear four or five spikes in each 5-inch pot. The flowers are up to 10 cm across and very colourful, with scarlet lateral sepals and the dorsal sepal, which forms a hood, pink veined with scarlet. Disa racemosa has taller inflorescences with smaller flowers, about 6 cm across, pink with deeper pink veining on the dorsal sepal. Disa tripetaloides is a more delicate plant with pale pink or white spotted with pink flowers borne on stems up to 30 cm high. Several hybrids involving these three species are grown, in particular Disa Kewensis (Disa uniflora X Disa tripetaloides) Disa Veitchii (Disa racemosa X Disa uniflora), and Disa Diores (Disa uniflora X D. Veitchii).
 

Disa tripetaloides

Disa cardinalis has smaller, intense scarlet flowers on flower spikes up to 40 cm tall and is much less common in the wild than the other species in the collection. Several plants of its robust progeny, Disa Kirstenbosch Pride (D. uniflora x D. cardinalis) are also grown. These were raised from a flask of seedlings sent by Kirstenbosch Botanic Garden. A pot full of spikes, each 100 cm or more high with many scarlet flowers, is a stunning sight.

In the wild, several species of Disa flower after fires have burned away all the vegetation surrounding them. It is thought that this enables their seedlings to grow without overwhelming competition from other plants and may account for the fact that disas can be difficult to flower in cultivation. At Kew the only species that does not seem to flower prodigiously is Disa racemosa, so burning it has not been tried!

The genus Stenoglottis is also native to South Africa, with one of the four species,  Stenoglottis zambesiaca, extending its range north to Malawi and Tanzania.

Stenoglottis firnbriata grows terrestrially or on mossy rocks or even low down on tree trunks close to streams and waterfalls where its leaves are sometimes bathed in spray and mist. The basal rosette of spotted leaves makes it an attractive plant even when not in flower. Each rosette produces a flower spike which may be up to 45 cm tall and bears up to 70 tiny flowers. The flowers are pink with purple spots and last for about six weeks in the late summer. After flowering the leaves die down for a brief dormant period. The tubers are repotted then, before the fresh new rosettes appear.

Stenoglottis longifolia is more vigorous than Stenoglottis fimbriata and produces a tuft of fresh green, strapshaped leaves. Its flowers are white or lilac with pink spots, the longest flower spikes growing to 70 cm tall. There are usually more than 100 flowers on each spike and these remain fresh from early autumn to the end of the year. Stenoglottis woodii comes into flower in the early summer and is smaller. The plants have white or pink flowers in short spikes.

Stenoglottis wodii

The genus Eulophia contains about 300 species which are spread throughout the tropical and subtropical areas of the world, the greatest concentration being in Central Africa. Most of the members of this genus are terrestrial but a great variety of habitats is utilised, ranging from dry grassland to swamps. Eulophia petersii grows among rocky granite outcrops in the Arabian peninsula, throughout tropical East Africa, and southwestwards as far as Namibia; with its hard fleshy leaves it can be said to be one of the very few really succulent orchids. It thrives well in its semi-arid environment and forms large clumps. The flowers are loosely spaced along a spike which can be over 3 m tall. The lip is white, veined with pink, while the sepals and petals are olive-green and curve backwards at their tips.

Probably the most sought-after species is Eulophia guineensis, a species from the equatorial regions of Africa, which can be found from Liberia eastwards to Ethiopia and Arabia and southwards as far as Tanzania. It grows in shady places, in the wild, in forests and in relict patches of scrub near rock outcrops or termite mounds. The plants are dormant for at least half the year, but the tall spike emerges with, or just before, the luxuriant leaves. The flowers are large and graceful, each with a large pale pink lip.
 

Eulophia streptopetala

Eulophia streptopetala comes from the grasslands and woodland margins of Africa, from South Africa north to the Yemen. The pseudobulbs grow just above the ground surface and give rise to the soft broad leaves and tall flower spike. The individual Flowers are bright yellow, with brown-spotted greenish sepals, and are very eye-catching.

One very distinctive feature of the African epiphytic orchids is that the majority of those in cultivation seem to have white flowers. This feature serves to make those plants with flowers of other colours all the more interesting. Two such genera are Bulbophyllum and Polystachya.

There are about 60 species of Bulbophyllum in Africa, all of which show great similarity in that they produce a procession of green pseudobulbs linked by short wiry rhizomes with a leaf or two on each young pseudobulb, the older ones being leafless. Their flowers and inflorescences are, however, varied. Bulbophyllum purpureorachis comes from tropical west Africa and Zaire and is huge by comparison with many other bulbophyllums. Its pseudobulbs stand about 6 cm tall and its rigid, leathery leaves are about 20 cm long. The flower spike takes the form of a large, dark purple knife blade that is spirally twisted and rises majestically above the plant. When this rachis is mature, the small purple flowers open in succession along both sides of its length over an extended period. By contrast Bulbophyllum falcatum, from Sierra Leone, has a flattened yellow green rachis with two rows of tiny red and yellow flowers along its midrib.
 

Bulbophyllum buntingii from Nigeria and Uganda has flower spikes about 12 cm tall with feathery, creamcoloured flowers which are fragrant. Bulbophyllum barbigerum is different again. In this species the lip of each flower is covered with red hairs of varying lengths rather like a woolly mat. These wave and bounce in passing air currents in a very bizarre fashion. All the tropical African bulbophyllums seem to thrive under similar cultural conditions. They are grown mounted on cork bark in a humid, semi-shaded environment where the temperature range is 15ºC (60ºF) to 27ºC (81ºF). They are misted over each morning.

Bulbophyllums on three

Polystachyas are unusual in having non-resupinate flowers, that is, they look as if they are upside down with the lip peeping out between the paired lateral sepals on the upper side of the flower. There are about 130 species of Polystachya, most of which come from tropical Africa.

Polystachya virginea, from the Ruwenzori Mountains in Uganda, Rwanda and Zaire, is a small plant about 20 cm tall bearing a cluster of helmet-shaped white flowers. The lip callus and the tips of the petals are yellow. Polystachya lawrenceana, a rare endemic from southern Malawi, forms a small hummock of fresh green, strap-shaped leaves over which hang the greyish green and pink flowers. Polystachya melliodora, named for its honey-like scent, comes from Mufindi District in Tanzania and the plant at Kew is part of the type collection. This interesting novelty was found in 1979 by Phillip Cribb and colleagues on a fallen branch in the montane rain forest of the Southern Highlands but has not been collected since. Each sparkling pure white flower has a cherry-red lip and petal margin, a striking colour combination. The Kenya species Polystachya bella has erect stems holding up to 20 gold or orange nodding flowers.

Tropical polystachyas are either mounted on cork oak bark or established in small pots of tightly packed epiphyte compost. An intermediate glasshouse with a winter night minimum temperature of 15ºC (60ºF) is used for them.

Ansellia africana is another African epiphyte or lithophyte with colourful flowers which, on a mature plant, are borne in great profusion. The scent of the flowers is somewhat overpowering, and one plant can easily perfume a whole greenhouse. The plant forms thick cane-like pseudobulbs up to 1 m long. The younger canes bear fresh green leaves while old canes eventually become leafless. The panicles of flowers arch out from the apex of mature canes and sometimes from the lower nodes of leafless ones. Each yellow flower is more or less heavily spotted or blotched with reddish brown. One dramatic feature of this species is the thick cluster of short spiky aerial roots which forms when the plant is grown in a hanging basket. Ansellia africana is grown at Kew in a light position in a glasshouse with a minimum night temperature of 18ºC (64ºF).
 
 

Angraecum

The white, pale yellowish or greenish-flowered African epiphytes are numerous and include the genera Microcoelia, Aerangis, Angraecum, Diaphananthe, Cyrtorchis, Bolusiella, Ancistrorhynchus, Mystacidium, Rangaeris and Tridactyle. A very large number of plants and species has been assembled at Kew in the last 40 years to facilitate the compilation of the accounts of the Orchidaceae for the Flora of West Tropical Africa, published in 1968, and for the Flora of Tropical East Africa, which was finally completed in 1989.

Microcoelia is one of a few genera in the Orchidaceae in which the plants have tiny brown scales instead of green leaves and the process of photosynthesis, by which the plant harnesses energy, is carried out in the roots. This curious adaptation is also found in the genera Taeniophyllum, from New Guinea, and Polyrrhiza from the Caribbean area. There are about 26 species of Microcoelia in Africa and Madagascar, eight of which are grown at Kew. They are cultivated on slabs of cork oak bark where they form tangled clumps of silvery roots and, in season, many arching racemes of tiny white flowers. They are grown in a light position in the glasshouse with a winter night minimum temperature of 15ºC (60ºF), with constant air movement and a high relative humidity.

Few species of the genus Aerangis are common in cultivation in Britain as yet, but they are sure to become more widely grown in future. Most of those at Kew are grown mounted on slabs of cork oak bark although a few are grown in pots of epiphyte compost. The graceful, arching inflorescences and starry, white flowers can be best appreciated when the plants are grown on bark and suspended from a suitable structure in the glasshouse. All the species are scented, especially in the evenings as darkness falls.

Aerangis verdickii occurs sporadically throughout East and Central Africa and is a vigorous plant with up to six greyish green leaves and strong, thick roots which grip the bark. Up to a dozen flowers are borne on each raceme and the long, sinuously curving spurs are tinged with green or pink. In A. mystacidii the spur is shorter and suffused with pink or orange. The dark green leaves indicate the need for a shadier position in the greenhouse for this species. Aerangis luteo-alba var. rhodosticta is very spectacular as its closely spaced, pale cream flowers are adorned with a bright vermilion column. It grows most luxuriantly in the shadiest position in a cool greenhouse. In brighter light the leaves are shorter and more succulent.

Two glasshouses with winter minima of 13ºC (55ºF) and 15ºC(60ºF) are used for growing Aerangis is and all the dark-green leaved species prefer a heavily shaded position. As with most orchids grown on bark, daily misting over seems to be beneficial for Aerangis.

 

Angraecum magdalenae

The genus Angraecum comprises some 200 species and encompasses an enormous variation in the form of the plants and size of the flowers. The large-flowered African angraecums, Angraecum infundibulare, Angraecum birrimense and Angraecum eichlerianum are mounted and suspended on a wire frame so that their slender stems can assume a natural position, partly upright and partly pendent. They are very different in growth habit from the glossy-leaved Angraecum distichum and the slender but usually upright Angraecum erectum. Some of the smaller species are grown in pots of appropriate size in a compost of coarse components while others are mounted on cork bark. A fairly light position in one of the warmer glasshouses seems to suit them best with high relative humidity. Daily misting is beneficial.

Madagascar

The island of Madagascar lies in the Indian Ocean off the east coast of Africa and occupies some 228,000 square miles. Its thick forests and remote mountains are the home of many fascinating animals and plants found nowhere else in the world. Some are related to the genera and species of the neighbouring continent which is only 300-500 miles away; others are completely different. Some of Madagascar's most exciting endemic orchids are grown at Kew, a selection of which are mentioned below.

Probably the best known orchid from Madagascar is the comet orchid, Angraecum sesquipedale . The eminent biologist Charles Darwin first investigated the pollination mechanism of this species by experimenting with live flowers sent to him by a well known orchid grower and author, James Bateman. The spur of the lip can grow to over 30 cm long, and Darwin surmised that in Madagascar there must be a moth with a proboscis long enough to reach the nectar at the end of the spur. In doing this, the moth would inadvertently pick up the pollinia from a flower from which it fed and leave them on the stigma of the next flower it visited, thus cross-pollinating it. Years later a moth with a very elongated proboscis was found, and Darwin's prediction is commemorated in its Latin name, Xanthopan morgani praedicta. The flowers of Angraecum sesquipedale are not always quite so large in cultivation but they are always very striking. The leaves are leathery and have a silvery bloom over their surface, making them quite distinctive.

Angraecum eburneum comes from the island of Reunion further east in the Indian Ocean, but its larger relative, Angraecum eburneum ssp. superbum is common along the north and east coasts of Madagascar and in the islands of the Comores group. It can grow up to 2 m tall and forms a thick clump of long, dark green, strapshaped leaves. The stiff flower spikes grow up to 1 m long and carry up to 20 flowers, which have pale green sepals and petals and a pure white lip.

Two hybrids in the genus are grown at Kew. Angraecum X Veitchii, registered in 1899, is a cross between Angraecum eburneum and Angraecum sesquipedale. It has the vigour and size of Angraecum eburneum and the enlarged flower similar to that of Angraecum sesquipedale. Angraecum Alabaster is a back cross of A. Veitchii with A. eburneum and has more but rather smaller flowers than A. Veitchii.

The large angraecums are grown in pots of appropriate size in a compost of coarse components while the smaller ones can be grown on cork oak bark. A fairly light position in one of the warmer glasshouses seems to suit them best with high relative humidity. Daily misting is beneficial.

Angraecum compactum is endemic to the high altitude forests of Madagascar and, at first sight, looks very different from the angraecums just described. It has fat fleshy leaves and grows to about 30 cm long at the most. The flowers, though, are instantly recognisable and are star-shaped, sparkling white and have a graceful curved spur.

Eulophiella roempleriana is a large plant which grows exuberantly in the Princess of Wales Conservatory. Its fat rhizomes branch and spread rapidly in several directions, producing vigorous clumps of large pleated leaves which grow up to 1 m long and are a fresh green colour when young, darkening as they age. In nature this plant is endemic to the forests on the east coast of Madagascar where it grows as an epiphyte in the crowns of Pandanus trees. Its spectacular racemes grow up to 2 m high and each bears up to 25 pink and red flowers.

Cymbidiella flabellata is rather similar in growth habit but much smaller and daintier. It is normally found in marshy places in the shade of other plants, its rather grassy foliage ensheathing narrow pseudobulbs which are well spaced on fine wiry rhizomes. The flowers are yellowish green with purplish black spots, except for the lip which is a bright rosy red.

Plants in the genus Aeranthes are grown in a shady humid glasshouse with a winter night minimum temperature of 16ºC (60ºF). They are suspended in hanging baskets from a suitable support above head height so that their pendulous flowers can be best appreciated. Aeranthes caudata has pale green flowers with long graceful petals and sepals while Aeranthes grandiflora has large flowers, up to 10 cm across, which are a translucent white with pale green tips to the petals and spur. Aeranthes ramosa has pale green flowers which dangle some 45 cm below the plant on stems as fine as threads.