I. INTRODUCTION

1.1 Background to and Outline of Study

This report was undertaken in connection with the FAO/IBPGR project on the Genetic Resources of Arid and Semi-arid Zone Trees, the aim of which is to foster the establishment of gene pools of tree species that will improve village life in these zones.

Several provenance collections of various trees will be made from countries where they occur naturally with a view to conducting comparative growth experiments in the participating countries.

It should be made clear that Acacia is a large genus with some 130 species in Africa and the Middle East. The present report focusses on only four species, with wide geographical distributions and complex variation patterns and of potential economic importance. It is important in conducting such provenance trials that the taxonomic identity of each sample is established as closely and accurately as possible and the aim of this report is to facilitate that. The four species are:-

1. Acacia albida

2. Acacia senegal

3. Acacia nilotica

4. Acacia tortilis

For each of these species a brief description will be given, with comments on recognition, relationships, distribution and a summary of previous taxonomic work. Under each species an account will be given of its variation, with descriptions of the formally recognised subspecies and varieties and keys where necessary. Attention will be drawn to problems still unsolved and suggestions made for future further study.

The synonymy is often complex. As most arises in Africa, and a full account with bibliography can be found in J.H. Ross's Conspectus of the African Acacia Species (Mem. Bot. Surv. S. Afr.) (1979), only the names of synonymes and their dates are cited in this report. An exception is made only for the Asiatic subspecies of A. nilotica not dealt with by Ross. Throughout the synonymy “A” is to be taken as short for Acacia.

1.2 Concordance

A report on the FAO/IBPGR Project has been published under the title “Genetic Resources of Tree Species in Arid and Semi-arid Areas” by F.B. Armitage, F.A. Joustra and B. Ben Salem (FAO, Rome, 1980). It may be helpful here to list the scientific names used in that report under the four Acacia species with their validity or otherwise in the light of the present report. It should be emphasised that this is only a nomenclatural exercise; it is not possible to be sure that plants referred to under these names are correctly identified without seeing them. Valid names are underlined; others, not under lined, are referred to what I believe to be their correct names:-

1.3 Occurrence of species, etc. in participating countries

In order further to assist the identification of material, it may be useful to list the species, subspecies and varieties concerned (according to this report) occurring in each of the participating countries:-

Senegal:- A. albida; A. nilotica subsp. adstringens, subsp. tomentosa; A. senegal var. senegal; A. tortilis subsp. raddiana var. raddiana.

Sudan:- A. albida (Race B, with intermediates with Race A); A. nilotica subsp. adstringens, subsp. nilotica, subsp. subalata, subsp. tomentosa; A. senegal var. senegal; A. tortilis subsp. raddiana var. raddiana, subsp. raddiana var. pubescens, subsp. tortilis.

Israel:- A. albida (Races A-B intermediates); A. tortilis subsp. raddiana var. raddiana, sunsp. tortilis.

P.D.R. Yemen:- A. nilotica subsp. indica; A. tortilis subsp. tortilis. This list is doubtless incomplete.

India:- A. nilotica subsp. adstringens (doubtful: see p. 30 subsp. cupressiformis, subsp. indica, subsp. subalata (doubtful: see p. 32); A. senegal var. senegal.

Fig. 1. Acacia albida (1) flowering branch (approx. x .4); (2) part of leaf-rhachis showing gland (approx. x 2.5); (3) juvenile shoot (approx. x .4); (4) flower (approx. x 3.6); (5) flower opened out to show ovary (approx. x 5); (6) anthers (approx. x 12); (7) pod (approx. x .4); (8) seed (approx. x .6). Reproduced from Flora Zambesiaca.