Yams (Dioscorea species L.) are among the most important of the tuber crops mainlyrncultivated in the tropics. They are also an important source of diosgenein, a startingrnmaterial for the industrial production of sex hormones and steroidal drugs withrnpharmaceutical properties. Despite their cultural and economic importance, there arerntaxonomic confusions in the groups called Guinea yams that belong to the D. cayenensisrncomplex. Identification of living or dried specimens using the currently used classificationrnscheme can be extremely difficult. Establishing the taxonomic identity and understandingrnthe systematic and genetic relationships among the accessions of Guinea yams and theirrnwild relatives is vital to the conservation and management of the crop. Therefore, the majorrnobjectives of this study were to evaluate the existing taxonomy and to determine thernamount and distribution of genetic variation within Dioscorea cayenensis complex inrnEthiopia. Collections of plant material were conducted between the months of July andrnSeptember 2005 and 2006 from different localities in South and Southwestern parts ofrnEthiopia.rnMorphometric analyses were carried out based on a similarity matrix constructed using 26rnmorphological characters on 40 accessions of Dioscorea cayenensis complex . The resultsrnof the cluster and ordination analyses revealed that the wild and cultivated Guinea yamsrnare closely related. None of the UPGMA clusters entirely contained those accessionsrnconsidered as discrete taxa according to the existing classification system.rnThe three primer combinations used in the Amplified Fragment Length Polymorphismrn(AFLP) analyses generated 158 scorable bands, with an overall polymorphism of 78%.rnOrdination and cluster analyses of AFLP data failed to produce any clear species boundaryrnbetween the species within D. cayenensis complex. The average genetic similarity betweenrnthe accessions ranged from 60 % to 100 %. The first, second and third principalrncoordinates axes cumulatively account 77.5 % of the total variation. AFLP analyses alsornrevealed a higher genetic divergence among cultivated Guinea yams accessions of thernSheko cultivars. Estimates of population parameters using microsatellite or simple sequence repeat (SSR)rnmarkers were made by studying 7 loci. The total number of alleles amplified for the 7 locirnwere found to be 60, with an average of 8.6 alleles per locus. Analyses of the datarnindicated that Guinea yams and their wild relatives in the study area displayed arntremendous genetic diversity. The wild forms exhibited greater allelic diversity than therncultigens. Contrary to what is expected in vegetatively propagated crops, none of the sevenrnloci studied showed a significant excess of heterozygotes. The levels of heterozgosityrnfound in the study group were, in most cases lower than expected. Analyses of therntaxonomic status using microsattellite data also revealed comparable results with bothrnmorphometry and AFLP. The accessions tended to group based on their geographicalrnorigin rather than their supposed taxonomic identity.rnIn the present studies, the phenograms and scatter plots based on morphological, AFLP andrnmicrosatellite markers failed to produce a clear partitioning of the study individuals studiedrninto discrete taxa according to the existing classification system. Therefore, we believe thatrnat least the wild or managed populations and cultivated Guinea yams of South andrnSouthwest Ethiopia form a single taxonomic entity. It also appears that the Shekornpopulation displayed the greatest genetic diversity. From a conservation perspective, it isrnimportant that both the range of cultivars and the diversity within them is protected bothrnin-situ in the Sheko region, and perhaps also in ex-situ in selected areas in gardens. Futurernstudies must be undertaken at the population scale and in a broad range of ecosystems, sornas to take the diversity of each of the yams currently regarded as distinct species intornaccount.rnKey words: Guinea yams, morphometry, AFLP, microsatellite, taxonomic status,rnGenetic diversity.