Every individual interacts in a variety of ways with a number of other individuals. Individuals of the same species, if situated spatially and temporally near enough to each other, compete, though ramets may compete or act as reservoirs of supply for each other according to circumstance. This is a simplified view of intraspecific relationships.

Species associations are interspecific relationships, and the following account must needs take the form of a rather broad review, since information derived directly from observation in West Africa is quite limited.

Interspecific organismal associations were termed symbioses by De Bary (1879), and a number of kinds of such relationship is now recognised. The named kinds are obviously different from each other, but there may well exist more such relationships, differing from each other in subtle and, as yet, undiscovered ways.

It is proposed to define symbiosis as provision by permanent or transient physical contact of one species for another. At least one nutrient or service of significance for the survival of at least one of the participants is involved and some degree of obligacy is present in the relationship.

This definition is wider than that of Boucher, James & Keeler (1982), but narrower than that of Starr (1975). It includes mutualism, in which the associate species confer benefit (exchange nutrients/services) on each other.

A family of trailing and climbing annual and tuberous perennial herbs in the warmer parts of the world, in West Africa common in the drier parts, though not as weeds. Since the publication of the account of the family in the Flora of West tropical Africa in 1954, several new genera have been recognised (names given in parentheses in the following account). The family is still probably undercollected, ♀ flowers and fruits of dioecious species mostly being needed. As the fruits are difficult to preserve and transport, local studies on plants grown from seed would be appropriate.

The West African genera almost all have Old World affinities, and are on the western edge of their range.

Members of the family may be recognised by their exstipulate, simple, digitately 3–7-lobed leaves, each accompanied by a tendril. Small cymes of ♂ flowers and (often) solitary ♀ flowers are produced, both kinds of flowers shallow, with five fragile, veined yellow or white petals. In the ♂ flower, each anther has only two loculi – it opens by one slit – and the anthers are often complexly folded. In ♀ flowers, the ovary is inferior and one-celled, with three stigmas.

Introduced species are of economic interest, though many species can be grown as decorative climbers.

A few genera can be distinguished on vegetative characters, but usually flowers and fruits are needed.

A family of tropical and subtropical trees and shrubs. Members may be recognised by their alternate compound pinnate exstipulate leaves with conduplicate ± opposite leaflets. Only Turraea in West Africa has unifoliate leaves, while Melia has bi- to tripinnate ones. The buds are either naked or protected by scales. Slash and wood are strongly scented and generally reddish. Lax, axillary, often large, panicle-like cymes of small, pale, scented flowers with a staminal tube are followed by capsules in most genera.

Decorative introduced species include Persian lilac (Melia azedarach) from India.

Turraea spp. are climbers in open situations in moist forest, are the only West African species of unusual habit.

Flowers ⊕, ♂ and ♀ on the same or different plants, but in Turraea, polygamous in Azadirachta and Melia; mostly 5-part, 4-part in Lovoa, where the sepals are orthogonal and the petals diagonal. K(5) small. C5 (C(5) in Turreanthus). A(8) or (10), joined only basally in most Trichilia spp., Pseudocedrela and Entandrophragma candollei, A5 in Cedrela and Toona; in these 2 genera there is an adrogynophore bearing petals, stamens and pistil; anthers are borne on or within the rim of the staminal tube. G(5) 5-celled, rarely with more cells (Turraea) or fewer (G(3) 3-celled in Trichilia, 1-celled in Heckledora), with 2 to many ovules per cell on axile placentae (2 parietal ovules in Heckeldora).

Pollination The flowers are scented and an intrastaminal disc is present in all except Turreanthus.

Ecologically important species in West Africa are mainly forest trees, especially in the drier parts of lowland forest. Few species appear north of the northern boundary of the forest-savanna mosaic. Nearly all the genera are Old World only in distribution.

Members of the family may be recognised by their alternate, digitately compound/lobed/nerved leaves with deciduous stipules and stellate hairs, and small flowers arranged either in clusters, sometimes on old wood, or else in lax, panicle-like cymes. Flowers are complex and five-part, about two-thirds of the genera having flowers with petals, the remaining one-third having at least some ♂ and ♀ flowers lacking petals. Fruits are also distinctive (see below).

Kleinhovia hospita, a shade tree introduced from India, is occasionally seen.

Byttneria is a tropical genus of lianes and scrambling shrubs, the only genus of this habit in the family in West Africa. There are three species in forest, the most common and widespread being B. catalpifolia subsp. africana in secondary forest. It has suborbicular leaf blades up to 18 cm Ø on petioles the same length. There are small, scented, white flowers in leaf-opposed cymes, the petals tailed, and the fruits are distinctively prickly capsules. The young shoots of the other species are also prickly.

Flowers ⊕ 5-part, either ♂ and ♀ and apetalous with a petaloid calyx, K(5) (Octolobus K(8)), or with petals, the calyx inconspicuous (spathe-like in Mansonia); polygamy can occur in both groups.

Herbs in the warmer parts of the world, including the New World, represented in West Africa by both annuals and perennials, the latter of quite diverse habit from erect, shrub-like and a few metres high to creeping plants rooting at the nodes or with various kinds of perennating organs (stolons in Pollia, rhizomes in Palisota spp., bulbs or tuberous roots in Cyanotis).

Members of the family may be recognised by their jointed stems bearing entire juicy leaves with convergent (parallel) venation, the blade arising from a closed sheathing base (sometimes with an intervening false petiole), its margins supervolute or involute when young. The flowers are small, threepart, delicate and short lived, in compound cymes, which are often subtended by spathe-like bracts. The fruit is generally a loculicidal capsule, and the seed always has an embryostega or operculum, a patch of testa (opposite the hilum), which is pushed off during germination.

Two species introduced from America are commonly grown in gardens. These are Rhoeo spathacea, with a rosette of purple and green sword-shaped leaves and white flowers, and Zebrina pendula, a trailing herb with purplestriped leaves and pink and white flowers.

Three genera are unusual in that the closed tubular sheath of the bract subtending the inflorescence is penetrated by the axillary inflorescence, which emerges through a hole. The genera concerned are Buforrestia, Coleotrype and Forrestia. Commelina is the only genus with leaf-opposed inflorescences, the remaining genera having the more common kind of terminal inflorescence.

A large family, present in both temperate and tropical parts of the world. Like the two families preceding, the pod is a common form of fruit, but it is less often woody than in the Caesalpiniaceae, and less often found in bunches than in the Mimosaceae. In West Africa, there are few tree species, but climbers, shrubs and especially undershrubs as well as herbs are common.

Mainly food and fodder species have been introduced, but the decorative species include several American and Asiatic species of Erythrina, Clitoria and Pueraria. Madre (Gliricidia sepium), from the West Indies, is popular as a hedge plant, as well as being useful for yam sticks.

Members of the family may be recognised by their alternate, stipulate compound leaves, which are often glandular and possess both pulvini and pulvinules. Leaflets are conduplicate and have stipels in about two-thirds of genera, but they often fall early and immature leaves must be examined. Stylosanthes erecta, a common seashore shrub, lacks stipels, as do several genera with paripinnate leaves (marked with an asterisk below). The flowers, described as ‘papilionaceous’, are distinctly zygomorphic, with the adaxial petal outside its neighbours. Nine of the 10 stamens are frequently joined in an abaxial trough, the tenth adaxial (vexillary) stamen, opposite the standard (vexilla) being free.

Compound imparipinnate or digitately trifoliolate leaves are common, but, although unifoliolate, compound paripinnate and digitate leaves are less common, they occur in so many genera as to be useless on their own for the purposes of identification.

Perennial forest herbs with sympodial fibrous or woody rhizomes and aerial stems bearing distichously arranged leaf sheaths or foliage leaves, both kinds eligulate, each stem ending in an ‘inflorescence’ (the synflorescence of Andersson, 1976). This is a compound bracteate cyme (synflorescence) with fragile flowers in pairs. This is a mainly New World family, with relatively few species in Africa, Asia and the Pacific area.

The leaves have open sheaths ± a false petiole, but always with a pulvinus (calloused portion) next to the leaf blade. In Megaphrynium and Thaumatococcus the pulvinus is particularly long, about 10 cm. The leaf blade is entire, ± ovate-elliptic and asymmetrical, one margin being ± parallel to the midrib, the other curved. Venation is close and pinnate, cf. Chapter 33, Zingiberaceae. In the bud, the straight-edged leaf half is rolled round the other half (ptyxis supervolute). Usually, corresponding halves of the leaf blade are either straight or curved (homotropy, Trachyphrynium), but occasionally leaves on one side of the stem will show symmetry consistently opposite to that of leaves on the other side (anitropy, Marantochloa congensis).

The aerial stems appear forked, often in a zig-zag way, but bear true lateral branches. Each branch bears a two-keeled prophyll (scale) as its first leaf on the adaxial side.

Various developmental patterns exist in the family, according to the relative development of aerial stems and petioles.

A mainly Old World family, represented in West Africa by only four genera and c. 45 species in diverse habitats, but mainly in forest. Aframomum and Kaempferia are tropical African in distribution, while Renealmia and Costus are chiefly American.

All are perennial herbs with fleshy rhizomes occasionally with tuberous roots, producing terminal cymose inflorescences of conspicuous ± sweetly scented flowers. The inflorescences are either carried separately on the rhizome from the unbranched leafy shoots or leafy pseudostem (formed, bananafashion, in Kaempferia and two species of Renealmia) or they appear as branches at the base of the leafy shoot. In some Costus spp., and Hedychium coronarium, the inflorescence is terminal on the leafy shoot, while in C. dinklagei and four West African species of Aframomum (amongst others), the inflorescences are lateral and the shoots bearing them hapaxanthic (Hallé, 1979). The leaves are arranged distichously, those of Aframomum, Alpinia and Renealmia in a plane at right angles to the length of the rhizome, those of Kaempferia, Curcuma, Hedychium and Zingiber in line with the rhizome. Phyllotaxy in Costus is spiral. Each leaf has an entire blade ± false petiole, and an open leaf sheath. There is often a ligule or a pair of ligules but never a pulvinus. The leaf blade is closely pinnately veined, the two margins symmetrical except perhaps at the very base.

The inflorescences can be congested and cone-like, with prominent spiral bracts.

A small pantropical family, represented in West Africa by three genera of ecologically prominent, large deciduous trees with ‘whorled’ branches.

Members of the family may be recognised by their alternate digitately compound leaves with deciduous stipules, large, robust, red or white, five-part flowers (produced while leafless), each with one-celled curled anthers on filaments variously united. The fruits are large capsules releasing seeds in wool, or indehiscent.

There are no genera of unusual habit in West Africa. In the sterile condition confusion with Ricinodendron (Euphorbiaceae) might be possible, but the latter has persistent stipules.

Balsa (Ochroma pyramidale) and Pachira spp. have been introduced, the former for its timber, balsawood (from which the Kontiki raft was made) and Pachira for its seed oil. Both seem to be planted only for decoration, and make fine specimen trees.

Flowers (÷ in Ceiba) ⊕, 5-part. Calyx lobed (Adansonia) or ± cupular. Corolla contorted. Stamens united to form a staminal tube, which is joined basally to the corolla, with filaments in bundles arising from its upper edge (free in Adansonia and Ochroma); anthers 1-celled, folded (linear in ‘Bombax’ sp.). G(2–5), with as many cells (opposite the petals) and stigma lobes as carpels; ovules 2 to many on axile placentae.

Pollination By bats in the white-flowered genera Adansonia and Ceiba, where the flowers have a characteristic stale smell. The red-flowered Bombax spp. are pollinated by birds, but the white-flowered ‘B.’ brevicuspe needs investigating. The deciduousness of the calyx in red-flowered species may give access to nectar.

A pantropical but especially Old World family of woody plants, found in West Africa mainly as shrubs, lower-storey trees and lianes in forest. Only four species are recorded for Gambia, Hexalobus monopetalus and Annona senegalensis in savanna, A. glabra in coastal swamps, and Xylopia aethiopica in forest-savanna mosaic.

Members of the family may be recognised by their two-ranked (alternate), conduplicate, simple, existipulate, entire leaves, aromatic wood and fragrant three-part, often downward-facing flowers, with many spirally arranged stamens and carpels. The fruits are also distinctive and contain large arilloid seeds, which are mottled or streaked in section (ruminate endosperm).

Artabotrys spp. are forest lianes with thick flat peduncles formed as hooks (Cremers, 1973), A. velutinus, a yellow-flowered species, being fairly widespread. The other c. 10 species in the genus are very locally distributed, as is common in many other genera in the family.

Flowers ⊕ and. Sepals 3, petals 3+3 (Uvariopsis ♂ or ♀ K2 C4; Enantia C3, the petals opposite the sepals; Hexalobus, Isolona C(6), Monodora C(3+3)). Stamens numerous, with a thickened connective, tightly packed in a spiral on the convex receptacle. G∞ free and spirally arranged (joined and in 1 whorl only in Isolona and Monodora); ovules 1 to several per carpel, attached to the adaxial carpel margin where the carpel is free, or basal (parietal only in Isolona and Monodora; Deroin, 1985).

PollinationAnnona is reported to be pollinated by beetles, but only handpollination seems to ensure adequate fruit-set.

A mainly tropical and woody family in which, in common with the previous family and the next one, the pod is the principal kind of fruit.

The family is relatively small in West Africa, its members being recognised by their bipinnate stipulate foliage with, in approximately half of the genera, one or more glands on the leaf rachis of petiole. The leaves often fold down if touched (Fleurat-Lessard, 1985) a response provoked by grazing herbivores, and likely to limit their predation. In so far as the existence of glands encourages the presence of an ant guard, these could also be construed as defensive. The leaflets are conduplicate in the bud.

The inflorescences are spikes or heads, brush like, and made up of small five-part actinomorphic flowers with prominent stamens. The pods, which follow, tend to hang in bunches.

Prickles and/or spines occur in a number of genera. Various Acacia spp. may possess stipular spines or prickles, and pseudo-galls may also be present. Dichrostachys has branch spines. The introduced weeds Schrankia leptocarpa (with four-angled stems, small balls of pink flowers and unjointed four-ridged pods) and Mimosa pudica (with terete stems, mauve flowers and flat-jointed pods) are prickly herbs. The indigenous M. pigra (also in Gambia) is a prickly riverside shrub forming tangles. Young shoots of the forest-emergent Cylicodiscus gabunensis and the swamp and riverain forest trees Cathormion spp. are also prickly.

Although very large on a world basis (20,000 species) the family is only modestly represented in West Africa, by under 300 species. These are mostly annual or perennial herbs or undershrubs, with alternate and/or opposite, simple exstipulate leaves, a few genera having milky juice (Berkheya and the Cichorieae tribe).

Members of the family may be recognised by the inflorescence, a racemose head ‘composed’ of very small flowers (florets), each gamopetalous and, if ♀ or with an inferior ovary. The axis (‘receptacle’) of the head is surrounded by an involucre of bracts, a feature also seen in Protea (p. 58), which fortunately possesses other distinguishing characters. The heads (in spikes) are ♂ (above) and ♀ (below) only in Ambrosia maritima, a whitely hairy undershrub in drier savannas. Compound heads (heads of heads) are seen only in Echinops and Elephantopus (white, blue or mauve heads), Sphaeranthus (red-purple heads) and Blepharispermum. B. spinulosum is a scrambling shrub (Côte d'lvoire– Ghana) with greenish-white compound heads, in forest regrowth. It is one of the few West African woody species and it has unique spines, one pointing down the stem from the base of each petiole.

In ‘woody’ species, no great quantity of wood is developed (see under Microglossa and Vernonia below). The remaining species which can be considered woody are of restricted distribution, i.e. Pluchea spp. in dry savannas from Sénégal to Sudan, Tanzania and Angola; Erlangea and Mikaniopsis spp. of upland shrubs and shrubby climbers from Guinée–E.

Superficially grass-like herbs, in ecological descriptions grouped with grasses as graminoids. The family is a mainly temperate one, occurring also in arctic areas. Most sedges are helophytes or mesophytes growing in seasonally wet places. There are a few hydrophytes in West Africa (Websteria confervoides and a few species of Eleocharis and Scirpus). West African species are mainly perennials, the widespread ones also tending to occur in most of the rest of tropical Africa at least. Less than half West African genera extend to Gambia. Habitat lists of species are to be found in Chapter 2.

Some of the terminology developed for describing grasses is also applied to sedges. The leafy erect aerial shoots (culms) are rosette shoots, the leaves mostly basal and separated from each other by only very short internodes. In perennial species, the culms arise from slender sympodial rhizomes, each culm terminating an increment of growth. The internodes of the rhizome may be long, resulting in a spreading habit, or very short, when a tufted habit similar to that of annual species results. Stem tubers are developed in at least two forms. Terminal tubers on stolons (Solanum tuberosum fashion) occur in nut grass (Cyperus rotundus), one of West Africa's most pernicious weeds, and the edible tiger nut (C. esculentus). Each tuber then produces a culm and several more stolons (but see Lorougnon, 1970).

A mainly tropical and subtropical family of varied habit, though all with opposite or whorled, exstipulate and sometimes fragrant leaves, often on four-angled stems. Ptyxis is conduplicate as a rule, conduplicate-plicate in Tectona. The inflorescences are racemose (less often cymose – Clerodendrum, Premna, and Vitex), but often congested, and made up of small five-part flowers with a two-lipped corolla, four stamens and a two- to eight-celled ovary with a terminal style. The fruit is a drupe, or a schizocarp splitting into four nutlets.

Several ornamental species have been introduced from tropical America, e.g. Petrea volubilis, a climber in which the persistent blue calyx lobes act like helicopter rotors in dispersing the fruit. Duranta repens (now D. erecta: Bromley, 1984), a shrub commonly planted as a hedge, has tubular blue flowers and yellow ‘drupes’. Lantana camara (wild sage or curse of Barbados) has short spikes of yellow or reddish flowers and does not set fruit in West Africa. In the West Indies it is probably pollinated by butterflies.

From tropical Asia, Gmelina arborea, with large flowers suitable for investigation, and Tectona grandis have been introduced as plantation trees, while Holmskioldia sanguinea (Chinaman's hat) and Clerodendrum spp., e.g. C. fragrans (now C. philippinum; Howard & Powell, 1968), are ornamentals.

Black mangrove (Avicennia Africana) is now placed in its own family Avicenniaceae, Congea tomentosa (with three large persistent bracts and bracteoles per flower) in Symphoremataceae. The former family is monogeneric, the latter trigeneric, both with free central placentation.

A cosmopolitan family, mainly of herbs, represented in West Africa by erect perennial herbs and undershrubs rarely over 2 m high, and a very few shrubs, in savanna and upland grassland. Apart from a few weed or culinary species introduced from the New World, our flora has only Old World affinities. Almost all West African genera have at least one species which also occurs in other parts of tropical Africa, sometimes in southern Africa and the Old World tropics in general as well; but within West Africa, most species have only local distributions. Gambia is recorded as having only five species (four genera), only Leucas martinicensis being indigenous.

Members of the family may be recognised by their four-sided stems bearing simple, exstipulate opposite or whorled leaves, which are often glandular and generally aromatic when crushed, small, toothed and either petiolate or sessile. Only lcomum (one to two species of tiny herbs in Guinée) has alternative leaves. The flowers are small, two-lipped, with four stamens, which usually lie on, or rise from, the bottom lip in West African species. White, pink, blue, violet and purple are common flower colours; yellow, orange and red are quite rare. Inflorescences are short axillary cymes, assembled in various ways into, for example, terminal and axillary interrupted spikelike structures (Ocimum), dense cone-like ‘spikes’ (Haumaniastrum, Hyptis), globular nodal clusters (Leonotis) or lax, spreading panicles (Englerastrum, Hoslundia). There is some doubt as to whether Haumaniastrum can be maintained as a genus separate from Acrocephalus (Robyns, 1966).

This is a small family in West Africa, of nine genera and c. 80 species, of entirely woody plants, trees, shrubs and lianes. Guiera is a monospecific genus endemic to West Africa, while Conocarpus and Laguncularia, of two species each, and Anogeissus (11 species), are each represented by a single species in West Africa. Only Combretum and Terminalia are represented by several to many species. All the above genera are, however, important ecologically, Terminalia also economically.

Members of the family may be recognised by their simple, exstipulate entire leaves and congested racemose inflorescences which may be axillary, extraaxillary or terminal. The flowers are small, actinomorphic and epigynous, and are followed by winged fruits. Both opposite (verticillate) and alternate leaf arrangements occur in the family. Ptyxis is usually conduplicate, in Quisqualis and Terminalia supervolute.

Introduced species include Terminalia catappa (Indian almond), a handsome tree with ‘whorls’ of branches and red senescent foliage. The fruit is a green fibrous drupe, which floats in water.

The indumentum (in all hairy species) is characteristically composed of non-glandular compartmented unicellular (‘combretaceous’) hairs, ± glandular multicellular stalked glands and ± glandular multicellular scales, these last being distinguishable by a hand lens. Quisqualis, for example, has stalked glands, Guiera scales, but Combretum spp. may have either, while Pteleopsis, Terminalia and Conocarpus have neither.