Molecular systematic studies in cycads: Evidence fromtrnL Intron and ITS2 rDNA sequences

The results of a pilot DNA sequencing study of cycads conducted at the new molecular systematics laboratory at Fairchild Tropical Garden are presented and assessed with reference to previous phylogenetic analyses and classification schemes based on morphology and anatomy. Two DNA regions were sequenced and analyzed for variation, an intron in the trriL gene in the chloroplast genome (trriL intron) and the internal transcribed spacer region between the 5.8S and 26S ribosomal DNA subunits (ITS2). The trnL intron proved to be relatively conservative among cycad genera, while the ITS2 region contained higher levels of variation. Parsimony analysis of the sequences suggests a number of relationships, some of which were inferred by previous morphological studies, some of which are new. The sequences ofCycas are the most divergent among cycads, suggesting the longest isolation.Dioon is relatively isolated from the other genera and contains two major clades.Stangeria does not appear closely related toBowenia but does seem to have a weak affinity withZamia andMicrocycas. Lepidozamia is more closely related toEncephalartos than toMacrozamia. Sequence variation among the species ofCeratozamia is low.Microcycas andZamia are closely related.