Distribution of orchids in Africa

The family Orchidaceae is the largest in the plant kingdom. With over 26 000 species, at a conservative estimate, it is much larger than its nearest rival, the Compositae, or daisy family. The latter is the larger in numbers of genera, however, with at least nine hundred compared with rather more than seven hundred in the orchid family.

Orchids are distributed throughout all parts of the world where plant life can exist and are most abundant in tropical areas where they form an important part of the vegetative scene, growing as epiphytes as well as terrestrial plants. The epiphytes are merely using other plants, usually trees or bushes, as a means of support, and are not parasitic on them in any way . Their roots extend into the air, among ferns and mosses which also grow on the branches, or over the bark of their support but have no connection with the actual tissues of the host plant.

Approximately one hundred and twenty genera of orchids are now recognized in the flora of the area embracing Africa south of the Sahara, the island of the Malagasy Republic (Madagascar), and the islands of the Seychelles, Comoro and Mascarene groups. Three quarters of these are endemic to this region and the others are mostly larger genera which occur in other parts of the world as well.

Although the number of genera in Africa and the islands of the western Indian Ocean compares favorably with other parts of the world the number of species in this area is not so impressive. For such a large area, where a great deal of botanical description and revision is still going on, an accurate estimate of numbers is very difficult to make. It seems likely, however, that there are between two and three thousand species, which is a small number for a whole continent compared with the wealth of species in some of the South American countries: in Colombia, for example, more than three thousand species have so far been recorded. The reasons for this paucity are twofold: firstly, vast tracts of the land mass are unsuitable as orchid habitats, and secondly none of the endemic genera are very large ones. More than seventy genera have less than fifteen species each and about twenty are represented by only one species.

In Africa, as in other parts of the world, the epiphytic orchids are most abundant near the Equator and gradually diminish in numbers towards the temperate zones where they are rare. In the area south of the tropic of Cancer as a whole there are approximately equal numbers of epiphytic and terrestrial genera. The distribution of these within the continent is closely related to the climate, rather than latitude by itself, however, and because most of Kenya, for example, is high and cool, or lower and very dry, the numbers of terrestrial and epiphytic genera are more or less equal, with a much greater diversity of species within the terrestrial group, although the Equator passes more or less through the centre of the country. The Congo, at the same latitude, is also a country of great variety but most of it experiences a much more equable climate with constant high humidity and frequent rain. Consequently it has a greater proportion of epiphytic species in its orchid . flora compared with Kenya. The island of Madagascar, although some way south of the Equator, is over one thousand miles long with a great variety of habitats suitable for orchids. Nevertheless the warm, humid climate of the east and northwest parts of the island has favored the development of epiphytes of many kinds and orchids with this type of growth are more numerous here, and on the neighboring islands, than terrestrial species.

The parts of the continent which experience a very long, hot, dry season provide very unsuitable conditions for epiphytic orchids. As one moves north or southwards away from the Equator they gradually disappear from all but the most favorable localities. The Republic of South Africa lies partly within the Tropical and partly within the Temperate belt yet of nearly five hundred species of orchids recorded in that country only thirty eight are epiphytes. Further more many of these are tropical species which can endure a wide variety of conditions and have extensive ranges throughout the_ continent.

A very large number of terrestrial species have become adapted to a period of dormancy during the long dry season. Having an underground tuber or rhizome which is protected from the scorching sun they can grow to maturity, flower, and set seed within a few weeks during the course of the rains. Such species are therefore widely distributed through out the extensive dry parts of the continent although many individual species seem to be somewhat restricted in their range, as are many of the epiphytes. The latter are often confined to quite small patches of forest or single mountain ranges. Other species are found only in certain easily defined conditions of warmth and humidity and reappear in widely separated countries wherever such conditions recur.

Because the conditions they prefer are so important to an understanding of the distribution of African orchids and their treatment in cultivation, we give next a summary of the main climatic types found in the continent and the vegetation they support. This is necessarily very brief but it serves to indicate the tremendous variety of climatic conditions, and therefore habitats, which exists in tropical Africa.

Climate and Vegetation of

Tropical Africa

The continent of Africa is shaped somewhat like a pear with its stalk end dividing the Indian and South Atlantic Oceans and its swollen end forming the southern coast of the Mediterranean Sea. It extends about five thousand miles from north to south, reaching the thirty fifth parallel in both hemispheres, and is second only to the continent of Asia with regard to the area it occupies. Because the Equator passes roughly through the centre of the continent a large part of the land surface is located between the tropics and the distribution of climatic and vegetation types is remarkably symmetrical. The plateau of high land which extends southwards from Ethiopia along the eastern side of the continent disturbs this symmetry somewhat as also does the enormously increased area of land in the northern hemisphere compared with the southern. Nevertheless the climate throughout the continent is closely controlled by the sun and its apparent migration between the tropics; hence the divisions between different climatic zones and vegetation types follow the lines of latitude fairly closely.

The climate of Africa is essentially hot and the rainfall unreliable. Most of the countries referred to in here fall within the Equatorial or Tropical climatic belts (see Map 3) where the average monthly temperature does not fall below 64°F. The movement of the sun brings two maxima of insolation to the equatorial zone and a single maximum to the tropical zones. Temperatures very largely follow the path of the sun, showing slight seasonal differences, and so does the rainfall belt, although this is usually subject to a lag. Broadly speaking, therefore, there are two rainy and two dry seasons in the equatorial zone and a single, longer, wet and dry season in the tropical belt every year.

This seasonal distribution of rainfall, however unreliable in amount, is the chief factor determining the growth of vegetation. The heavy and regularly distributed rainfall of the Equatorial and Tropical Marine climates supports a moist tropical forest often referred to as rain forest. Away from the Equator and the eastern coasts forest growth becomes impossible as the dry season lengthens. Woodland and scrub or scattered trees among tall grasses with a marked seasonal growth cycle become the characteristic vegetation types of these parts. The dependence of plant growth on the availability of rain is clearly shown in Maps 1 and 2.

The Equatorial zone

In Africa a true Equatorial climate affects a zone which extends 5°N and 5°S, and from the edge of the Atlantic Ocean to about 10°E. Temperatures are uniformly high and extremely constant with the thermometer hovering around 8o°F throughout the year. Extremes of 1oo°F and 6o°F are rarely encountered and the annual range is usually only about 5°F. The diurnal range is much greater, sometimes reaching 15-25°F and the nights seem pleasantly cool in comparison to the daytime. On the east side of the continent the high land from 30°E eastward brings the temperatures down but the annual range is still small and the regime is essentially an Equatorial one.

Since the temperature varies so little throughout the year rainfall becomes the feature which determines the four seasons in this area. These are alternately wet and dry, or wetter and drier, with the rainfall maxima occurring after the March and September equinoxes. The rainfall is heavy and convectional at both these seasons, frequently falling during the afternoon and evening after a morning of bright sunshine. During the 'long rains' of March-May Nairobi receives an average of 17 inches (Entebbe (Uganda) 25 inches; Lagos (Nigeria) 39 inches in May-July) while in the 'short rains' of October-December only 8 inches fall (Entebbe, I3; Lagos, r6 in September-November). Throughout this zone, however, there is some rain in every month and although the humidity is greatest during the wet seasons it is at all times high, somewhat oppressive for human beings except at Nairobi and other places at higher altitudes, and ideal for plant growth.

The moist tropical forests which are characteristic of the Equatorial zone are evergreen and contain a great variety of trees of varying height. The canopy is very deep, usually starting fifty to sixty feet above the ground and with taller emergent trees extending it to a hundred and twenty or a hundred and fifty f et. Below the canopy a tangle of creepers and lianes is mixed with a dense growth of herbs which makes penetration of this kind of forest extremely difficult.

On the high plateau of eastern Africa at this latitude a distinct sub-type, the High-altitude Equatorial climate, occurs between 5,000 and 10,000 feet above sea level. Temperatures are lower and although the annual range is still small the diurnal range is much greater, as much as 40°F, and the climate resembles that of the tropical areas further from the Equator in this respect. The rainfall regime is the same as that throughout the Equatorial latitudes, although the total is less. Nairobi (5,500 feet) receives an annual average of 39 inches while much of the west African coast receives more than 1oo inches.

The lower rainfall and humidity on the plateau precludes the development of rain forest except in small isolated patches. Elsewhere there is a complex mosaic of drier montane forests, deciduous woodland and grasslands of various types which provides an interesting landscape and a great variety of plant spenes.

The Tropical zones (a) Marine

Tropical Marine climates are encountered from 100S to 30°S on the eastern side of Africa and on the eastern side of Madagascar. They are distinguished from the Equatorial type of climate by the single maximum of rainfall although some rain, often in the form of mist or drizzle, falls throughout the year. Another feature of this type of climate is the prevalence of violent storms, known locally as cyclones, from December to March which particularly affect Madagascar and the other islands of the western Indian Ocean and some times the neighboring mainland of Africa as well.

At the northern end of this belt temperatures are the same as in the Equatorial climates. At the southern end, in Natal, there are sufficient seasonal differences, up to 13°F in the average temperature, for the recognition of winter and summer.

Along the coast a narrow belt of mangrove vegetation occurs in low brackish areas and along estuaries. Behind this, and extending to the eastern edge of the plateau, is a belt of moist tropical forest. Formerly this was fairly continuous but it has been disturbed by cultivation and commercial forestry activities and now forms a complex mosaic with deciduous woodland and savannah.

(b) Continental

Climates of the Tropical Continental type are the most extensive in Africa next to the Desert type. They are found in a broad zone on either side of the Equatorial type and are distinguished from it by the single maximum of rainfall. A further distinction is that for the rest of the year, often as much as eight months, there is complete drought. Humidity is low during the prolonged dry season and insolation intense, so that very high temperatures, often over 90°F, are recorded. At the same time the cloudless night skies allow considerable radiation and the fall of temperature is rapid. Before dawn the thermometer often records less than 50°F and night frosts are by no means uncommon during the cool season. Temperatures soar higher as the dry season continues, the sun reaches the zenith, and the rains approach. It suddenly becomes much cooler with the breaking of the rains although the increased humidity and the much lower diurnal range of temperature at this time make living conditions uncomfortable.

Nevertheless the rains have a magical effect on the vegetation and landscape. Dry watercourses become flowing rivers and the dusty surface turns into mud or a rich green sward. The scorched vegetation bursts into new green and reddish growth, bulbous plants put up their flowers and the seeds of short-lived flowering plants quickly germinate. In the woodlands and mixed grass woodlands which dominate the scene plants of every kind make extremely rapid growth in preparation for a long period of dormancy during the next dry season.

The length of the rainy season becomes progressively shorter towards the higher latitudes. The amount and reliability of the rainfall also decreases and while 50 inches is common on the Equatorial margin 10 inches is the average amount at the fringes of the desert. Stations in between may have anything between these two amounts and a drought in one year may be followed by floods the next.

The higher altitudes covered by this type of climate, as in the Equatorial regions, experience lower temperatures and a lower annual rainfall. A more or less open woodland with a ground flora dominated by grasses is characteristic of the areas with a pronounced dry season and moderate rainfall. In the drier areas conditions do not support the growth of perennial grasses. An ephemeral ground flora of grasses and herbs combined with xerophytes and succulent plants is mixed with trees, mainly of the genus Acacia, in a type of vegetation known as Grass Steppe. This is widespread across Africa at about 15°N, on parts of the plateau of East Africa and southwards in Botswana and the highlands of Madagascar. It grades into a sub-desert Steppe in the still drier areas on the margins of the tropical belt where widely spaced shrubs are the only perennial feature of the vegetation.

Orchid habitats

Some of the many kinds of vegetation found between the varied coastline and the snow-capped mountain peaks of tropical Africa have been mentioned in the preceding pages. Orchid plants are found throughout the entire range, from mangrove swamp and sand dunes to the alpine conditions near the snow. They are distributed through bush, forests and grasslands alike, although many individual species are severely restricted in their range.

The basic types of vegetation are described very briefly below as separate entities: these types are usually clearly defined but are often very limited in extent. Within the space of a few hundred yards one can pass from tall grassland through a belt of woodland into moist tropical forest. As the dominant trees change different conditions are available for epiphytic and terrestrial orchids. We have accordingly described the main features of forest, woodland, savannah, bushland and grassland as they occur in Africa noting particularly the conditions within them which affect the growth and distribution of orchids. With a few exceptions we have limited the examples cited to the genera described in the main part of this book where further details of the ecological preferences of some of the species and their precise distribution are given.

Forests

Many types of forests are differentiated on detailed vegetation maps of African countries but all are composed of tall trees with. Interlacing branches often several storeys high. The canopy is usually dense enough to inhibit grass growth and the herbaceous plants of the forest floor are all shade lovers. Calanthe, Liparis and some species of Habenaria are among the few orchid genera which prefer this kind of shady and protected habitat.

The rain forests of the Congo and other parts of west Africa are the tallest types with most of their trees a hundred and twenty to a hundred and fifty feet high and with an abundance of woody climbing plants among the tall straight trunks. This type of forest also occurs in Uganda and in a few places along the East African coast as well as in parts of Madagascar and the Comoro Islands. Rain forests are always evergreen because there are always some trees with leaves in the canopy although individually all the trees are deciduous. Angraecum infundibulare, Eurychone rothschildiana and some species of Vanilla, and in the Malagasy region various species of Aeranthes, can be found on the tree trunks or among low secondary growth in these shady forests. Most epiphytic orchids are not shade lovers, however, and grow low down only where the sunlight has managed to penetrate a gap in the canopy or where the trees are more widely spaced so that the canopy is less dense. Along the sides of streams, near clearings and at roadsides, many species of Polystachya and Bulbophyllum are common. They are much more abundant a hundred feet or more above the ground among the branches and twigs of the canopy itself. Some of the more unusual and uncommon orchid species, including Ancistrochilus rothschildianus and Oberonia disticha, are found here too.

The forests of the East African mountains, particularly those over 6,ooo feet above sea level are made up of shorter trees. Many of them also experience distinct seasons as far as rainfall is concerned, with a drier season of two or three months following each similar period of heavy rain. The epiphytic orchids which grow in them are adapted to periods of alternate wetting and drying out. Some of those which occur only in these areas of relatively dry, montane forests have the most extensive aerial roots to accommodate them to this way of life. Several species of Aerangis are abundant here in shady places while some of the Cyrtorchis and Tridactyle species, with their thicker, much more leathery leaves, are found in brighter light, sometimes even in direct sunlight. Polystachya and the leafless Microcoelia both have their representatives in this type of forest and the unusual Brachycorythis kalbreyeri is found in the wetter parts. The 'cloud forests' of the higher and wetter situations, with their abundant covering of epiphytic mosses and lichens on every tree, support large numbers of epi phytic orchids of rather few species of Tridactyle, Bolu siella, Angraecum, Polystachya and a few other genera. Drier forests are found at the margins and lower levels of these mountains, particularly on the western slopes. The prevailing winds, being mostly from the southeast or northeast, have lost a good deal of the moisture they carry by the time they reach the western side of the mountains, but even here there are specjes of Chamaeangis, Diaphananthe, Tridactyle and Rangaeris which appreciate fresh air and a complete drying out in between periodic soakings. In the rainy season these forests are cool, sometimes shrouded in mist like the 'cloud forests,' and the plants are damp all day; but in the dry weather they are exposed to bright sunlight and strong winds so that the humidity is very low except when the temperature falls at night.

Among the terrestrial genera Habenaria, Bonatea and Eulophia are all represented in these drier forests and at the higher altitudes, especially near streams, species of Satyrium, Disa and Brachycorythis also occur.

Woodlands

Woodlands of various kinds are very extensive in Africa and often merge with forests, especially the drier types. They are usually distinguished from them by the fact that the trees are of approximately the same height and spaced so that their crowns touch forming a light but more or less continuous canopy. They are made up of many different species of tree which are usually all deciduous during the dry season so that they are leafless for several months during the hottest part of the year.

Only a few epiphytic orchids can tolerate exposure to strong light for such long periods. Ansellia gigantea is probably the best-known species; it occurs on palms and baobabs in some of the hottest and driest parts of eastern Africa. Even in parts of the Luangwa valley, in Zambia, which has a dry season of eight months, it flourishes many miles away from the slightly increased humidity of the river banks. Acampe pachyglossa occurs there too, but, as in the other inland parts of eastern Africa where it is common, it is usually confined to trees on or near the banks of perennial rivers. Some species of Bulbophyllum and Polystachya, which have coriaceous leaves and drought resistant pseudobulbs, also occur in these woodlands but, like the two species mentioned above, they are usually found on the lowest branches or the trunks of the trees where they can enjoy a certain amount of shade in the hottest part of the year. A few xerophytic species of Tridactyle and Cyrtorchis, which have thick, succulent leaves, and the leafless genus Microcoelia are the only other epiphytic genera encountered in wood lands at low altitudes, while the genera ]umellea, Angraecopsis, Rangaeris and Ypsilopus are also represented in woodlands at higher levels as well as in the dry montane forests with which these woodlands merge.

The number of terrestrial species in African woodlands is very hard to estimate but is certainly large. Most of them have underground tubers or rhizomes of various kinds which send up a flowering stem before or during the onset of the rainy season. They have a short life of only a week or two and many of the plants do not bloom every year. Together with the fact that they flower when travel becomes most difficult this means that many species are known from only a single gathering and there are probably others waiting to be discovered. Eulophia and Habenaria are the largest genera encountered in this type of habitat, where the soil often remains undisturbed for many seasons and the vegetation above it is removed by burning every year. Impeded drainage on small areas within the woodlands prevents the growth of trees and produces a grassy 'dambo' which has an extremely rich orchid flora.

Savannah

Savannah is a term of Spanish origin used to denote an open mixture of trees and shrubs standing in a tall growth of grass. From the point of view of species composition there are many different types of savannah but they all result in a landscape with a park-like aspect and are subject to frequent grass fires. Terrestrial orchids of several genera occur among the grasses although they are frequently hidden by them and overlooked by collectors. Some of the most attractive species of Eulophia are found in these perennial grasslands, often flowering shortly after the vegetation has been burnt when they show up well against the charred earth with its fresh green shoots of short grass.

Very few epiphytic orchids occur in the savannah vegetation except where this merges with woodland or a small strip of forest near a stream. Some of the tougher epiphytes which can endure a partly xero phytic existence can be found here, including Cyrtor chis arcuata, Rangaeris amaniensis and some of the Microcoelias.

Bushland

Small trees which branch or fork from the base cover great tracts of the continent, particularly in eastern Africa, forming a thicket or bushland vegetation. This is of varying density, sometimes evergreen and sometimes deciduous, and on its drier margins the bushes become more widely spaced forming a steppe and eventually a semi-desert type of vegetation.

Two distinctive orchids, Polystachya tayloriana and Eulophia petersii, are found only in this type of vegetation. There are a few epiphytic orchids, mostly those which also occur in the woodlands, but they are rare. The terrestrials are fewer than in the woodlands although some species of Bonatea and Habenaria seem to prefer the shelter given them by low growing Acacia or Commiphora bushes in the areas with a higher rainfall and are frequent there. A few species of Eulophia, and of one or two small, little-known genera, also flourish in more favorable places within this vegetation type.

Grasslands

The pure grasslands, and those of the savannah country, offer a very different habitat for herbaceous plants compared with the woodlands and bushland where grass is also the dominant plant of the ground flora. In the latter there is always a certain amount .of shade from the sun and protection from the wind but in the true grasslands most of the associated plants are completely exposed. Nevertheless a wide variety of terrestrial orchids occurs in these grasslands, particularly at the higher altitudes near the Equator and also at higher latitudes further south.

As mentioned earlier most of the orchid flora of the Republic of South Africa is terrestrial and some predominantly South African genera such as Disa and Satyrium extend their range northwards to the montane grasslands of other parts of Africa. Most of these are extremely difficult, if not impossible, to grow in cultivation, however, and they have not been included in here.

There are several kinds of grassland where drainage is impeded, either permanently or seasonally, for various reasons, and these all have their characteristic orchid species. Permanently waterlogged conditions give rise to swamps where several species of Eulophia thrive. These can be transplanted rather easily to damp situations in gardens or maintained without difficulty in a non-porous container.

The seasonally moist grasslands, which are variously referred to as vlei, mbuga or dambo in different parts of Africa, , have a much richer orchid flora and even though such an area may be only a few acres in extent many different species of Eulophia, Disa, Satyrium and other genera can be found there. The nature of the habitat, with its alternating conditions of airless moistness and desiccation, is very difficult to reproduce. The species which seem to prefer it are rather ' rarely seen in cultivation, at any rate in flower, and seem to be as difficult to transplant as those of the cooler grasslands of South Africa.

Habenaria, Bonatea and several species of Eulophia are common in the grasslands of the savannah regions but most of these are also rather difficult to bring into cultivation. The Eulophia species with pseudobulbs above the ground present few problems and of the tuberous rooted genera Bonatea seems to be easier than others. Many efforts with some of the spectacular Habenarias, and Eulophias with chains of underground rhizomes, have been unsuccessful.

Collecting Orchids

Collecting indigenous orchids is a hobby enjoyed by many orchid growers today, not only in Africa. In fact most amateur growers in tropical regions start off with the local species and when their interest and enthusiasm spreads they import exotic species and hybrids from other parts of the world. Flowering orchids are also collected by botanists but usually in very small numbers; their specimens in herbaria increase our knowledge of the variety and distribution of this fascinating family of plants.

The number of plants and species which is removed from wild situations by these two groups are limited and except in the case of plants which are already rarities there is no threat to the continued existence of the species. This is no excuse for denuding the forests, however, and collectors should always be selective, choosing only the plants which are the most suitable size for transplanting. Usually these will be small or medium-sized, well-developed plants. The smallest ones will be left to grow under the best possible conditions, and the largest ones to flower and produce seeds which will ultimately replace the plants that are removed.

There are certain other rules which should be observed by collectors, both local residents and visitors alike. Few African countries have laws prohibiting the collection of orchid plants; however intending collectors should always find out if there are such laws in the countries concerned and obtain permission to collect from the local Department of Forestry or Agriculture if necessary. Most countries have Nature Reserves and National Parks of various kinds, some times covering quite large areas. Although originally established to conserve wildlife or forests these are often total nature reserves and no plants may be collected in them without permission from the authorities. But there are plenty of places outside these areas where orchids abound. In many parts of Africa there are settlement schemes, tsetse clearance zones and irrigation projects, where the forest or bush is being removed at a great rate for cultivation. By removing orchids and other rare plants from these areas the collector is active in the cause of conservation, especi ally if the plants can be propagated from seed in cultivation, and enhances the variety and interest of his own collection at the same time.

Digging up terrestrial orchids presents few problems provided adequate tools, which must sometimes include a pick-axe, are available. The tubers and rhizomes are often deeply situated and any which are damaged will fail to survive. They should be removed with as much soil as possible adhering to them and their roots and placed without disturbance in a tough brown paper bag, or a plastic bag if this is kept open. The worst time to try to transplant ground orchids is when they are in flower, but as they are often very difficult to locate before or after this stage it is some times impossible to avoid this.

Epiphytic orchids are much more commonly sought after and are frequently more difficult to obtain. The problem first of all is to reach them and secondly to detach them from the host plant without damaging too many of their roots. Unless one is extremely agile one is limited in many forests to areas where felling is going on and the topmost branches of the trees are brought to ground level. It is only when examining fallen trees that one really appreciates the numbers of epiphytes which occur within the canopy and it is very pleasing to be able to salvage some of those which would otherwise die. Small epiphytes are best collected on the branches on which they are growing and a small hacksaw is easy to carry around for this purpose. Larger plants can usually be detached by hand or with a broad-bladed knife so that at least some of the younger roots remain intact.

Where an exciting epiphyte high above you catches the eye you must either climb the tree yourself or employ a local child to do so. The latter sounds simple but is not really the best technique as it is difficult to explain to the uninitiated, especially when there are language problems, exactly which plants you want and how they are to be obtained and sent down to you. If you choose to climb yourself this can be made much easier by wearing climbing irons. They need to be designed to fit the boot of the climber and a pair made by a small hardware firm for a few shillings have proved most successful on several occasions.

The alternative to climbing is to have some kind of mechanical grab which can be operated at the end of a long pole. Suitable poles can sometimes be cut in the forest but there is never a long enough one around when you most want it and they are apt to be very heavy and unwieldy. Instead we have used a set of light metal poles which interlock and can be added to as the occasion demands. Each one is six feet long and the set is easily carried in an old fishing rod case. In practice we have found more than three of these poles difficult to cope with-they have an annoying habit of coming apart just as one is within reach of the orchid but an improved design could probably get over this difficulty. The top pole has a forked hook which is not difficult to manipulate and orchids ten to twenty feet above the ground on trunks, and on small leafy branches where they would otherwise have been unobtainable, have been collected with this apparatus fairly easily.

Once the plant has been gathered it is best to trim off dead leaves and old or damaged roots straight away. Only the newly developing roots will be of use to the plant in re-establishing it so there is no point in retaining the old roots, which are likely to be damp, and to be the first parts to cause rot to set in or spread, while. the plants are being taken home. Slugs, snails and insects should be searched for and discarded at this stage too before the plants are packed into a basket or carton.

The safest way to move newly acquired plants is to have them loosely but firmly packed in a cool dry container. Newspaper makes good wrapping material as it insulates the plants and prevents one damp or diseased plant from contaminating any others. Plastic bags of various kinds are useful for terrestrial plants and small, delicate epiphytes, provided they are kept very cool and unsealed, and are inspected from time to time. If allowed to become too damp or warm they quickly spell death to their contents.

The wrapped plants, or small branches bearing plants, are most conveniently carried in straw baskets. Locally made ones of various kinds are available cheaply in all parts of Africa. They are light and easily carried in the hand but also fairly tough and cool.

When travelling from place to place by vehicle it is most important that the plants should be kept cool and shaded. They should never be packed in the boot of a car, left unprotected on the deck of a boat or placed on the spare seat on the sunny side of a light aeroplane. It is surprising how much heat is absorbed by a moving vehicle under intense insolation, let alone when the vehicle is stationary. A load of plants, or even a few in a basket, should never be left in a vehicle parked in the sun. If there is no shade for the vehicle the plants must be taken out and placed in the meagre shade the vehicle itself provides, but not forgotten or run over when you move on again.

On a trip lasting only a few hours or over a weekend the important factors are to keep the plants cool and sufficiently firmly packed to prevent them bruising each other if the journey is rough. A collecting trip lasting longer than this has the additional problem oflooking after the plants as you go along. In the early days of a two or three weeks safari it is tempting to leave plants until later so that they will have a better chance of survival until you reach home. On the whole it is best to collect the plants as and when you find them for you may well decide to return by a different route or forget the exact locality of something which would have been really worth having.

When operating from a base such as a hotel or camp looking after the plants is not too difficult. Keeping them spread out in a shady place free from visiting slugs and mice is the best procedure, and if they can be sprayed with water several times during the early part of warm days so much the better. Travelling daily from place to place, collecting plants as you go, presents more difficulties and in this case it is necessary to be very selective. Only the most healthy plants at the best stage of growth for transplanting, usually some of the smaller ones, should be taken. At the end of the day, when you are tired and only wanting food and rest, the plants must come first. No matter how many miles have been tramped the plants collected that day must be tidied up and wrapped and those from earlier days inspected and aired before the collector can consider his personal needs. However tempting to do so it is often quite fatal to leave the plants until the next morning.

Most countries in Africa do not restrict the export of indigenous plants. In common with countries in other parts of the world they do have rules regarding the import of plants and usually require that the plants should be inspected by their entomologists on arrival and that the plants should be accompanied by a Phyto sanitary Certificate from their country of origin. Visiting collectors must find out what the regulations are in their own country before they leave home. They will not find it difficult to obtain plant health certificates, if required to do so, from the Department of Agriculture of the countries where they have collected plants, and can then be assured of arriving home with the plants without difficulty. Failure to comply with the regulations can result not only in delays which may be fatal but even in the destruction of the plants.

Growing Orchids

Many books and articles have been written about orchid growing and we do not propose to duplicate the excellent information they contain. We have decided to include some details which need to be borne in mind when cultivating African orchids, however, for two reasons. When we first started to grow them ourselves we followed the conventional instructions in some of the standard textbooks. These gave excellent results for the exotic species and hybrids which we also grow, but we did not get the best results with most of our indigenous species in this way. By trial and error we have found methods which suit most of the species described in this book, but we are still at the experimental stage with some others. The second reason is that visitors from other continents, who also grow orchids in their homes, have frequently commented that they have not seen certain local techniques used before. It seems that there are certain features of the cultivation of some African orchids, particularly the angraecoids, which need to be emphasized. The definitions given in this section should be borne in mind when reading the cultural notes relating to each species in the main part of the book.

The most important point in orchid cultivation, which applies to the cultivation of many other plants as well, cannot be over-emphasized and it is that the three essentials of culture-light, humidity and temperature-should be in balance with each other. To give two examples: Ansellia plants from exposed situations in the warm, humid, low altitude regions of equatorial Africa flourish when transplanted to higher elevations, such as Nairobi, where the temperature and humidity are lower than in their natural surroundings, provided they are lightly shaded during the brightest part of the day in sunny weather. They will survive if fully exposed to the sun but in the drier atmosphere the leaves will be very yellow, if not actually burnt, and this is not good cultivation. Besides spoiling the look of the leaves light which is too strong has an inhibiting effect on growth and plants may be stunted and malformed when grown in unbalanced conditions. Similarly an epiphytic orchid brought down to Nairobi (5,500 feet) from about 8,ooo feet on Mount Kenya will need to be grown in a shadier position than the tree top where it was collected, to counteract the higher temperatures it experiences at the lower level.

The growth of plants is most rapid where light, humidity and temperature values are high. Many orchids are naturally very slow growing, however, and prefer cooler, less humid and more shady co_ndi tions for their healthy development. Nevertheless their rate of growth can often be increased without harm, so that flowers are produced twice a year instead of once, when the plants are removed to suitable, well-balanced conditions in cultivation.

Light

The strong light in which many African orchids grow naturally without burning, and without which they will not flower, is constantly surprising. In all the tropical regions of the world daylight is as strong throughout the year as it is in London or New York during sunny days in June. The only respite comes in the first and last hours of daylight and on cloudy days when the sun is completely or partially obscured. While many people wear shady hats and dark glasses in order to survive comfortably in the tropics there are several orchids which need to be fully exposed to the same light in order to thrive.

In the descriptions which follow strong light means fully exposed to the natural tropical light; light shade means as much shade as is provided by a tree with a thin canopy such as Croton megalocarpus, certain species of Eucalyptus, or the silver birch in temperate regions. Such shade is usually transient and the plant is exposed to alternating short periods of direct sun and shade. This degree of shading is not so heavy as semi-shade, which describes conditions in which the plant receives about 5o% of direct light. This is available in short periods of alternating full light and complete shade.

These conditions are fulfilled in lath houses in which orchids are frequently grown in the tropics, or by the use of slatted screens placed over greenhouses at right angles to the diurnal path of the sun. Deep shade means a situation in which direct sunlight is never received by the plant and is equivalent to the amount of light received on the forest floor which is protected from direct sunshine by several layers of leaves.

These four values apply to light conditions in tropical regions and growers further north or south will need to qualify them in regard to the conditions they provide because the strength of light available to start with is lower.

Fresh air and humidity

A number of the orchids described in here grow in windy and exposed positions and most of them live where the air is fresh with constant breezes even though the latter may be humid. Many growers in tropical regions keep their plants out of doors in the fresh conditions to which they are accustomed. In temperate regions, where a greenhouse is essential at least in winter, maintaining a fresh atmosphere is extremely important. Normal ventilation often pro vides an inadequate amount of fresh air movement and usually cannot be increased without loss of heat which is provided at considerable expense. In these circumstances, particularly in a small greenhouse, a fan keeps the air moving in winter while the air is cool and damp and, in conjunction with more ventilation, has a cooling effect in summer when temperatures can soar dangerously.

Stagnant, humid air should be avoided at all times. It is particularly dangerous if there is a large temperature gradient between day and night time providing good conditions for the invasion of bacterial and fungal infections. Provided there is plenty of air movement humidity can be maintained at 65-70% during the day when temperatures are in the 70-8o°F range; the humidity will reach higher levels at night when the temperature falls, with beneficial results. Without any air movement, and particularly at the lower temperatures experienced during the winters of temperate climates, humidity should be much lower. Generally speaking conditions which feel comfortable to a human being will be suitable for most orchids ; thus dry cold is easier to bear, and more successfully endured by orchids, than damp cold.

Temperatures

For some of the plants described in here we have been able to give exact temperature requirements, but for most of those with a wide distribution we have been deliberately vague. The reason for this is that many of them are adaptable and can accommodate themselves to the situation the grower provides. In the text cool applies to the conditions which plants experience when growing at an altitude of over 6,500 feet at the Equator, or lower at higher latitudes, where temperatures may fall to 45°F or less at night and reach 70-75°F during the day; intermediate applies to conditions between 3 ,ooo and 6, 500 feet at the Equator, where the temperature is in the region of 6o°F at night and reaches 8o°F or more during the day; warm applies to the lower altitudes, where plants live in a temperature of 65°F or more at night with a corresponding amount of heat during the day.

Containers

Before being potted up and mixed with an ex1stmg collection newly collected plants must be carefully cleaned, preferably with fungicidal and insecticidal solutions as well as soapy water. Terrestrial orchids and most of the pseudobulbous epiphytes can be grown in clay or plastic pots, in various fibers or composts to suit the individual species, in the conventional way. Many of the African orchids which are classified among the angraecoids do not do well with this treatment, however, and some refuse to grow at all. Several angraecoids thrive in the more open conditions of a rustic cedar or redwood basket filled with osmunda, tree fern fiber or bark. Their long aerial roots need plenty of space and the ability to drain quickly and dry out after watering. For this reason they also do well on tree fern slabs suspended in plenty of fresh air.

In our experience, however, nearly all these species grow best in their natural way, that is, clinging to a section of a tree limb. If they can be collected on a living branch and taken home already established all they need is to be treated with an effective insecticide before being added to the collection. Otherwise almost any durable, non-resinous hardwood will be found suitable as a support. A branch from a living tree is better than a half-dead log from the woodpile and those with a slightly rough bark usually give the best results. Wood with a very thick or rough bark is often but not always, unsuitable as it consists of so much dead material; this will quickly rot, or produce large mushroom-like growths, under orchid growing conditions.

The key to success, as with growing orchids on tree fern slabs, is to tie the plants on to the host branch very tightly in the beginning. All old roots more than a few inches long should be removed and a pad of osmunda or living moss inserted under the young roots. The plant and moss are then tied tightly on to the log with nylon fishing line, copper wire, or some other resistant and durable material which does not offend the eye. Some people use sisal string or raffia twine which has the advantage that it gradually rots as the plant grows on to the log and can be removed easily when it is no longer required. If the timing is not quite right, however, the plants may fall off just when the new roots were about to fix themselves on to the bark and several months' patience is wasted. Holes are easily drilled in the log in order to attach labels and supports, or wires if it is to be hung vertically.

Once fixed on to the log the treatment of the plant for the few months it takes to establish itself is most important. Because its roots, and therefore its absorbing powers, are small and transpiration is continuous it needs to be sprayed with water several times a day to prevent shrivelling of the leaves. Provided these remain firm and glossy roots will soon develop and spraying can be cut down to once or twice a day.

This method of growing orchids has the advantage that a number of plants can be established together producing a very effective display when they flower.

Watering, drainage and resting

Although the majority of orchids are moisture-loving plants their demands for fresh air are at the same time considerable. In their natural surroundings heavy storms soak the plants but the water drains away immediately and as soon as the rain ceases they begin to dry out. The aerial roots, which swell up with water and appear green during the rain, shrink and whiten as air replaces the moisture which is absorbed into the plant from the outer layers of cells.

Heavy watering with quick drainage, and dry periods between successive watering, will imitate the natural conditions of most species and promote healthy growth. Water should only be supplied at a rate at which the plant can make use of it, however, so that the intervals between watering in a very humid environment, where the roots dry out more slowly, will need to be greater than in a drier one. Every grower must determine how long these intervals should be in the conditions he provides.

The host trees of most epiphytes, like the orchids themselves, grow most quickly and flower during the rainy seasons. After flowering the rate of growth slows down, and stops altogether in the dry season when there is often a complete or partial leaf fall front the trees. This allows more sun and air to reach the epiphytes and slows down their growth in turn. Similarly in cultivation, after flowering and the completion of a new growth, whether it is a leaf or a pseudobulb, many orchid plants need a rest. This can by induced by increasing the light and decreasing the water supply, and is necessary to ripen the new growth and promote flowering during the following season.