Molecular Ecology (2001) 10, 1947–1958 © 2001 Blackwell Science Ltd Blackwell Science, Ltd Geographical patterns of genetic variation in two species of Stylosanthes Sw. using amplified fragment length polymorphism M. C. SAWKINS,*† B. L. MAASS,‡ B. C. PENGELLY,§ H. J. NEWBURY,* B. V. FORD-LLOYD,* N. MAXTED* and R. SMITH¶ *School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK, ‡Institute of Agronomy in the Tropics, Georg-August-University, Göettingen, Grisebachstr.6, D-37077, Göettingen, Germany, §CSIRO Sustainable Ecosystems, Indooroopilly, Qld 4068, Australia, ¶The Royal Botanic Gardens, Kew, Richmond, Surrey, UK Abstract Understanding the extent and distribution of genetic diversity within a species is essential for the development of effective conservation strategies. The objective of this study was to assess genetic variation using amplified fragment length polymorphisms (AFLP) in two species of the tropical legume genus Stylosanthes Sw. Annual, S. humilis (2n = 20) and perennial, S. viscosa (2n = 20) are found throughout tropical America, and are sympatric for much of their range of distribution. One hundred and eleven accessions, covering a wide geographical range, were selected for AFLP analysis. Binary data matrices derived from DNA banding patterns were analysed using the software programs NTSYS-PC and ARLEQUIN. Several accessions were found to be misidentified. Of the S. humilis accessions, the overall average similarity value was (0.72) slightly higher than the value obtained for S. viscosa (0.67). Cluster analysis and principal coordinate analysis grouped accessions from both species by geographical origin, with a few exceptions. Analysis of molecular variance ( AMOVA) in S. humilis revealed 59.4% of the variation among groups formed from the cluster analysis. This was highly significant (P < 0.001). For S. viscosa AMOVA also revealed more variation among than within groups (66.5%). This was also highly significant (P < 0.001). The majority of accessions of both species conserved ex situ are of Brazilian and Venezuelan origin. This study has identified areas in Central America and Mexico for which novel genetic variation may be found and where conservation activities should be focused. Keywords: AFLP, conservation, genetic variation, geographical distribution, Stylosanthes humilis, Stylosanthes viscosa Received 19 January 2001; revision received 3 May 2001; accepted 3 May 2001 Introduction Stylosanthes (Aubl.) Sw. (Fabaceae, Papilionoideae, Aeschy- nomeneae, Stylosanthinae, Polhill & Raven 1981) comprises 30 –40 species and is found throughout the tropics and subtropics of the Americas, Africa and South-East Asia. The genus consists of herbaceous or suffruticose perennials and annuals up to a height of 1.5 m. Members of the genus are considered colonizers, found principally in open ground, along roadsides, grassland with low scrub and open woodland (Edye 1987). Considerable research has been undertaken into the genus since the discovery, over 50 years ago, of its use in improving pasture. The greatest impact has been the improvement of pasture in dry tropical regions of the world (Edye 1987, 1997). Species have been used as cattle fodder, as a cover crop and a green manure (Gardener 1984; Gillard & Winter 1984; Thomas 1984). The two species considered in this study are Stylosanthes humilis and Stylosanthes viscosa. S. humilis is an annual diploid species (2n = 20), found throughout tropical America, and is also adventive in Australia. In the Americas, it has a distribution similar to that of S. viscosa and is found from Mexico, Central America, through Colombia, Venezuela and Brazil. It is thought to originate primarily from Venezuela and Central America (Williams et al. 1984). It has previously been Correspondence: M. C. Sawkins. †Present address: Department of Ecology & Evolutionary Biology, 321 Steinhaus Hall, University of California, Irvine, CA 92697–2525, USA. Fax: +949 824 2181; E-mail: msawkins@uci.edu