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Plant function and evolutionary biology
REVIEW

An overview of actinorhizal plants in Africa

Maher Gtari A and Jeffrey O. Dawson B C
+ Author Affiliations
- Author Affiliations

A Laboratoire Microorganismes et Biomolécules Actives, Département de Biologie, Faculté des Sciences de Tunis, 2092 Tunis, Tunisia.

B Department of Natural Resources and Environmental Sciences, 1316 Plant Sciences Laboratory, University of Illinois at Urbana–Champaign, 1201 South Dorner Drive, Urbana, IL 61801, USA.

C Corresponding author. Email: jdawson2@illinois.edu

This paper originates from a presentation at the 16th International Meeting on Frankia and Actinorhizal Plants, Oporto, Portugal, 5–8 September 2010.

Functional Plant Biology 38(9) 653-661 https://doi.org/10.1071/FP11009
Submitted: 12 January 2011  Accepted: 24 June 2011   Published: 16 August 2011

Abstract

A compilation and synthesis of information derived from plant databases and other sources on the occurrence, diversity and geographic distribution of actinorhizal plants in Africa is presented in this review. Actinorhizal plants are a specific group of non-leguminous, woody dicots having symbiotic, nitrogen-fixing root nodules that are induced on roots of actinorhizal plant species by soil actinomycetes of the genus Frankia. There is a lack of basic information on actinorhizal plants in Africa compared with other major land masses in the world. Results indicate that most, if not all, African countries and climatic regions have native or introduced actinorhizal species. A synthesis of available information indicates that there are six families, nine genera and 38 reported species of actinorhizal plants in Africa. Of these, 21 species are native and 17 are exotic. The families and corresponding number of species in each genus are: Betulaceae (native Alnus glutinosa (1), exotic Alnus (2)); Casuarinaceae (exotic Casuarina (5), exotic Allocasuarina (3), exotic Gymnostoma deplancheana (1)); Coriariaceae (native Coriaria myrtifolia (1)); Myricaceae (native Morella (19), exotic Morella cerifera (1)); Rhamnaceae (exotic Ceanothus caeruleus (1), exotic Colletia paradoxa (1)); and Elaeagnaceae (exotic Eleaegnus angustifolia (1)). Four reports of native, actinorhizal Ceanothus species in Africa found in the database were determined to be false, instead, being non-actinorhizal species. Widespread plantings of exotic Casuarinaceae have been introduced into tropical and arid zones of Africa as multipurpose trees, especially in arid regions where native species do not occur. There is a diverse assemblage of native species of Morella in Africa, mostly shrubs or small trees, which provide medicine, other useful chemicals and wildlife habitat. Many native Morella species are isolated in montane islands, apparently leading to greater speciation than in Eurasia from where the genus migrated into Africa. The current status and knowledge of African actinorhizal plants indicates a need to focus research on their biogeography, biology, ecology, genetics and use.

Additional keywords: actinorhiza, African plants, Frankia, nitrogen fixation, nitrogen-fixing trees.


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