II. A. ALBIDA

2.1 A. albida: Relationship

A. albida is a very distinct and systematically isolated species, without any close relatives.

2.2 A. albida: Generic position

As indicated (p.6) Chevalier (1934) separated A. albida from the rest of Acacia as Faidherbia albida (Del.) A. Chev. The following are some of the unusual or anomalous characters supporting this:-

1. Tree leafless during rains, leafy in dry season (see below).

2. Seedlings produce bipinnate leaves from start (no pinnate leaves).

3. No gland on petiole, but glands between all pinna-pairs.

4. Stamen filaments shortly connate at base.

5. Anthers large, eglandular.

6. Pollen polyads 30-celled; pollen tectum with large areoles.

Other anatomical and biochemical evidence is referred to by Polhill & Raven (1981). Most recent authors have maintained A. albida within Acacia, although often with hesitation. Elamin (1977) considered it as an Acacia, but “in a monotypic group to emphasize its anomalies”. Ross (1979), after summarising the differences, wrote - “Although differing from the other African acacias, A. albida does nevertheless share many characters in common with them. It may ultimately prove better to transfer the species to Faidherbia”. Polhill & Raven (1981, p.170), however, consider that A. albida should be placed in a separate genus Faidherbia.

2.3 A. albida: Recognition

Although it is not possible to indicate a single feature that alone makes recognition of A. albida certain, yet it shows so many unusual characters combined that recognition is normally easy and without doubt. It is normally a sizeable tree leafy in the dry season but losing its leaves with the rains. The leaf-petioles always lack a gland (a rare feature in this group of Acacia), but there is a gland on the leaf-rhachis at the junction of each pair of pinnae. The stipular spines are straight and the inflorescence elongate. The very characteristic pods, orange or red-brown, coiled, falate or twisted, and indehiscent, have given A. albida the popular and apt name “Apple-ring Acacia”. A. albida shows other very unusual characters less obviously seen.

Although Davidson & Jeppe (1981) state that A. albida is the only Acacia with straight spines and elongate inflorescences, and this is true for Southern Africa, other species in tropical Africa share these features.

2.4 A. albida: Summary of previous taxonomic work

A. albida was first described as long ago as 1813 by Delile from a specimen collected in Egypt. As will be seen from the synonymy on p.7, a few specific names described during the nineteenth century, and a few varieties also, have been found not to be separable. In general, however, the synonymy of A. albida is limited, because it is an easily recognisable and taxonomically isolated species.

It has been however, fairly recently subjected to two detailed studies both from the taxonomic and other viewpoints (Ross, 1966; Wickens, 1969). Its distribution in Israel and the Near East has been analysed by Karschon (1961). Its relationship with other African Acacia species has been set out by Ross (1979). A good general account of A. albida is given in Anon. (1979).

Chevalier (1934) considered that the anomalous features, especially the stamen filaments shortly connate at the base, were sufficiently important to justify the placing of A. albida in a new monotypic genus Faidherbia. The matter is discussed more fully under 2.2 on p. 5.

2.5 A. albida: Brief description

Usually a tree 4–30 m high, sometimes shrub-like. Trunk usually solitary, up to 2 (rarely to 6)m in diameter. Bark brown to dull grey or whitish, rough and somewhat corky, scaly and fissured. Young shoots ashen to whitish. Crown rounded in outline and spreading, with branches often drooping in mature trees. Spines paired, 0.2–3.2 cm long, stipular in origin, straight, never enlarged or inflated, especially when young often tipped with orange or brown. Leaves shed at start of dry season; new leaves produced at the start of the rainy season. This may occur twice where (as in East Africa) there are two rainy seasons. Davidson & Jeppe (1981) state that it may bear leaves all the year round where there is no waterlogging. Leaves bipinnate. Petiole eglandular. Pinnae 2–12 pairs, with a single conspicuous gland on the rhachis at the junction of each pair. Leaflets 6–23 pairs per pinna, glabrous to pubescent, 2.5–12 mm long, 0.7–5 mm wide. Flowers in a spicate inflorescence 3.5–15.7cm long borne on a peduncle 0.8–6.3 cm long; flowers creamy yellow, sweetly scented. Stamen filaments shortly tubular at base. Anthers 0.2–0.4 mm across, eglandular even in bud. Pods bright orange to reddish brown, falcate, curved into a circular coil or twisted, when straightened out 6–35 cm long and 1.4–6 cm wide, indehiscent. Seeds 11–29 per pod, lying transversely to long axis of pod.

Fig. 2. Acacia albida. Habit. of large tree near Omaruru railway bridge, Namibia, S.W. Africa (J.D. Keet)

2.6 A. albida: Synonymy

A. albida Del. var. senegalensis Benth. (1842)

A. saccharata Benth. (1842)

A. gyrocarpa Hochst. ex A. Rich. (1847)

A. mossambicensis Bolle (1861)

Prosopis? kirkii Oliv. (1871)

A. albida Del. var. microfoliolata De Wild. (1925)

A. albida Del. var. variofoliolata De Wild. (1925)

Faidherbia albida (Del.) A. Chev. (1934)

2.7 A. albida: Distribution

The main area of distribution of A. albida is Africa, where in the northern part of the continent it extends from Senegal and Gambia in the west to Egypt, the Sudan (see Elamin, 1977), Ethiopia and Somalia. It extends southwards through East Africa to the Transvaal, Natal and Lesotho, and going westwards south of the equator to Angola and Namibia.

Wickens (1969) refers to a single doubtful record from Libya but possibly an introduction.

Beyond Africa A. albida occurs as a native in the Yemen and also in Israel and Lebanon.

It has been introduced into Ascension, possibly the Cape Verde Islands (Wickens, 1969), Cyprus and Pakistan (Ali, 1973).

Fig.3. Acacia albida. Map showing approximate distribution of the species and races.

2.8 A. albida: Variation

Brenan (1959) drew attention to the occurrence of the two well-marked geographical races in East Africa:-

1. with young branchlets glabrous or almost so, also the inflorescence-axis, calyx and corolla; leaflets ciliolate on margins otherwise glabrous or nearly so, usually rather small, to 6 mm long and 1.5 mm wide.

2. with young branchlets pubescent, also the inflorescence-axis, calyx (and often corolla); leaflets pubescent on surface, often larger than in A, and up to 12 mm long and 4 mm wide.

No formal taxonomic names were given to these races as too many intermediates are present in certain parts of their ranges. Ross (1966) states: “The characters typifying each of Brenan's races are not necessarily correlated, appearing more as inconsistent tendencies so that, as mentioned by Brenan, intermediates possessing attributes of both races are common”.

However, this confusing situation is only found in certain areas. The geography of these two races has been studied and extended by Ross (1966) and Wickens (1969).

As Ross (1966) states, all specimens (with the exception of a few doubtfuls) from the southern part of the range of the species are referable to race B, which is the only one to occur in South Africa, Lesotho, Namibia, Zimbabwe, Zambia, Mozambique, Malawi and Tanzania (except for Northern, Tanga and Eastern Provinces). Race A is the only one to occur in Northern, Tanga and Eastern Provinces of Tanzania, Uganda, Kenya, Ethiopia and Somalia. In Sudan, Ethiopia and West Africa, race B is common but many specimens combine the small leaflets of race A with the pubescence of race B, while others are glabrous as in race A, but with the large leaflets of race B. In Egypt and northwards to Lebanon, the specimens are mostly intermediate between A and B, usually with somewhat pubescent leaflets, but smaller than usual in B. Probably the same applies to the Yemen, but the material is inadequate. In Cyprus glabrous leaflets are prevalent, but larger than usual in A.

It may be noted that A. albida var. senegalensis Benth., var. microfoliolata De Wild. and var. variofoliolata De Wild. are all referable to race B.

2.9 A. albida: Further work needed

It would appear that races A and B (p. 9) have rather different geographical ranges and thus very possibly different ecological and climatic tolerances. It would be useful to have trials of comparative performance. Also, the provenance of seed is likely to be an important factor in the success or otherwise of introduction programmes for A. albida.

2.10 A. albida: Literature consulted and cited