Eulophia horsfallii ( sometimes called E.rosea) is a magnificent, tall-growing, purple-flowered orchid found in KwaZulu-Natal, Mpumalanga and Limpopo [Northern Province] in South Africa as well as in Swaziland and further north in tropical Africa. In a remarkable adaptation from the humid, summer rainfall and winter drought conditions of its natural habitat, this species has become naturalized at Kirstenbosch Botanic Garden under seemingly unsuitable conditions of heavy winter rains and dry summer heat.

Description
Reaching a staggering 2.3 m high in full flower, E. horsfallii is a large terrestrial orchid, producing several broad, erect, heavily pleated leaves and a robust flower stem carrying up to 40 large purple flowers with cream-coloured, crested lips. It often remains evergreen under cultivation in temperate climates but is deciduous and summer-growing in the wild, and has a subterranean, rhizomatous rootstock consisting of persistent pseudobulbs linked together by short, cylindrical stems, similar to those of the popular orchid genus Cymbidium.

Distribution
E.horsfallii has a wide distribution in Africa, occurring from northern KwaZulu-Natal in a northerly direction into Swaziland, Mpumalanga and Limpopo in South Africa, and further north to Sudan, west to Angola and Congo, and along the coastal parts of West Africa.

Derivation of the name and historical aspects
The generic name Eulophia is derived from the Greek eu, meaning well, and lophos, meaning crested, and alludes to the prominently crested lip or labellum, situated below the two lateral petals of the flowers of this genus. This species has recently been referred to as E.rosea see below. The specific epithet horsfallii honoured Mr J.B. Horsfall, who cultivated and flowered the type material of this species, collected in West Africa, in his glasshouse in England, and which was beautifully illustrated in Curtis's Botanical Magazine in 1865.

In June 2011 SANBI received the following interesting communication from Mr Peter Morrall:

"My great grandfather, George Morrall, head gardener and estate bailiff to Thomas Berry Horsfall, was the first to cultivate a species of orchid new to England, when Mr. Horsfall was sent a plant specimen from Mr. S. Cheetham, Calabar River, Nigeria, in 1861. Thomas Berry Horsfall was a Member of Parliament and a shipping merchant working out of Liverpool. The orchid flowered in the glasshouses at Bellamour, Colton, Staffordshire, in 1864, and was subsequently registered in London by George Morrall, with the  name ‘Lisochillus Horsfallii'. The species was reported lost to cultivation until March 1906, when Mr. Walter Rothschild, of Tring Park, Hertfordshire, received a silver gilt Flora Medal from the Orchid Committee of the Royal Horticultural Society."

However, it later became apparent that this plant had earlier been described as Lissochilus roseus by John Lindley in 1844, and illustrated the same year in Edwards's Botanical Register. Then, in an issue of Orchid Review in 1964, A.D. Hawkes transferred Lissochilus roseus to the genus Eulophia as E. rosea, and placed Eulophia horsfallii in synonymy, however this seems to be in dispute now.

Ecology
In its natural habitat, E. horsfallii grows in humid, dappled shade on swamp forest margins. The individual flowers are long lasting (up to two weeks) and the flowering period is lengthy, beginning in September and extending to March, with a peak flowering period between November and the end of February. At Kirstenbosch its flowers are pollinated by large, black-and-yellow bumblebees that result in the formation of large, green, pear-shaped seed capsules. The tiny dust-like seeds of orchids are very well adapted to wind dispersal, and this undoubtedly accounts for the spontaneous appearance of numerous plants of E. horsfallii in the Camphor Avenue at Kirstenbosch, a short distance from the bulb nursery where the original plants are cultivated in large containers. Evidently, ideal conditions of moisture, light, temperature and a suitable fungus exist between the decomposing logs (that form the terraces in the Camphor Avenue) for seed germination and development to occur there. Plants of E. horsfallii have also spontaneously appeared relatively long distances away from the bulb nursery, including the grounds surrounding the Gold Fields Education Centre, and in a swampy patch near the Harry Molteno Library.

Growing Eulophia horsfallii

E.horsfallii grows well in full sun but prefers a protected, lightly shaded position such as that provided by established evergreen trees with a high canopy. Under all-day full sun conditions the leaves tend to burn, and strong winds cause the leaves to tear and look unsightly. A loamy, slightly acid soil containing well-decomposed compost is preferred, and the plants grow equally successfully under well-drained or waterlogged conditions. At Kirstenbosch Gardens they easily survive heavy winter rainfall and remain largely evergreen, sending up their new leaves in spring and summer, before the old leaves have died down. In summer rainfall areas experiencing cold, dry winters, the plants become dormant over the winter period. Once established, the clumps plants like to remain undisturbed for several years and rapidly form thick clumps. This species can also be successfully cultivated in large, deep plastic pots with a diameter of at least 35 cm. Frequent, heavy watering is required in summer, especially for container grown plants that need drenching twice weekly.

Division of E. horsfallii clumps is the only feasible method of propagation for the home gardener. Thick clumps are best separated in early spring, just before the new leaf shoots begin to develop. The rhizomatous rootstock consists of persistent pseudobulbs which are usually entirely subterranean, and linked by short, cylindrical stems. The rootstock forms branches with age, and these branches can be separated, ensuring that each branch is removed with a growing point. Separated branches must be replanted immediately, and kept well watered, and will require a year or two of good growth before flowering commences again. The major reason that most orchids (including Eulophia) cannot be raised successfully from seed when sown in the normal way is that the seedlings of most of them are dependent for survival on a symbiotic association with a specific fungus. Symbiosis refers to the association of two different organisms living attached to each other, or one within the other, usually to the advantage of both. In the instance of orchid seeds, the fungus penetrates the roots of the seedling and through the exchange of nutrients, nutritional benefit is obtained by the seedling, and usually by the fungus as well. Further requirements for successful germination of most orchid seeds include sufficient moisture and favourable temperature and light levels.

As with most Eulophia species, the foliage of E. horsfallii is highly susceptible to infestation by red spider mite in summer, seen as a silvery bronze sheen over the lower leaf surface. The developing flower buds frequently fall prey to attack by aphids and thrips at the height of summer, resulting in malformed blooms.

References

• DUNCAN, G.D. 1989. Eulophia. In N.M. Du Plessis & G.D. Duncan, Bulbous plants of southern Africa. Tafelberg, Cape Town.
• DUNCAN, G.D. 2000. Eulophia horsfallii at Kirstenbosch. Veld & Flora 86: 16-18.
• HAWKES, A.D. 1964. Notes on Lissochilus and Microstylis. Orchid Review 72: 27
• LINDER, H.P. & KURZWEIL, H. 1999. Orchids of southern Africa. Balkema, Rotterdam.
• POOLEY, E. 1998. A field guide to wildflowers of KwaZulu-Natal and the Eastern Region.Natal Flora Publications Trust, Durban.