Cycads are an ancient group of gymnosperms that were abundant and widely distributed during the Mesozoic, but are now largely confined to isolated tropical and subtropical regions. Many cycads are currently threatened with extinction and there is an urgent need for more information about their taxonomy and genetics. Extensive molecular studies of cycads were initiated at the molecular systematics laboratory set up in collaboration with Florida International University, utilizing the world renowned cycad collections at Fairchild Tropical Garden and the Montgomery Botanical Center. The 11-12 genera of cycads currently recognized are thought to comprise a monophyletic group, classified as a single order, the Cycadales, which is divided up into three or four families. Analysis of morphological characters could not fully resolve all the genera. We studied cycad phylogeny using a variety chloroplast genes and spacers (trnL intron, trnS-trnG, psbB-psbF, atpB-rbcL) and nuclear regions (ITS). The results of this study are presented and assessed with reference to previous phylogenetic analyses and classification schemes based on morphology and anatomy. Cycas is the most divergent genus, followed by Dioon, which is also isolated from the other genera and contains two major clades. Stangeria appears to be related to Ceratozamia, Zamia, and Microcycas. Lepidozamia appears to be more closely related to Encephalartos in Africa than to Macrozamia. Sequence variation among the species of Ceratozamia is especially low. DNA fingerprinting studies were also initiated with Microcycas to try and find molecular markers for sex determination of seedlings and markers for future conservation genetics projects.

Key words: cycadales, cycads, DNA, gymnosperms, phylogeny, sequencing