Abstract: Pistacia is an economically important genus because it contains the pistachio, P. vera, which has edible seeds of considerable commercial importance. The evolutionary history of the genus and the taxonomic relationships among the species are equivocal. This study is part of a comprehensive phylogenetic study that has been conducted on this genus in order to refine taxonomic and evolutionary relationships by utilizing different types of data (including morphological, cytological, anatomical and molecular). We aim to investigate the evolutionary and taxonomic relationships among Pistacia species. Here we present the first investigation of the leaf structure in all Pistacia species. The following species were studied: Pistacia aethiopica J.O. Kokwaro, P. atlantica Desf., P. chinensis Bunge, P. eurycarpa Yaltirik, P. falcata Becc. ex Martelli, P. integerrima Stew. ex Brand., P. khinjuk Stocks., P. lentiscus L., P. mexicana HBK, P. mutica Fisch. and Mey., P. palaestina Boiss., P. terebinthus L., P. texana Swingle, P. vera L. and P. weinmannifolia Poiss. ex Franch. Leaflets of P. vera, which have random orientation, were isobilateral, while leaflets of the other species were dorsiventral and were oriented horizontally.