BOGLER, DAVID J.* AND JAVIER FRANCISCO-ORTEGA. Research Center, Fairchild Tropical Garden, 11935 Old Cutler Rd, Miami, FL 33156. - Phylogeny of the cycads (Cycadales) based on chloroplast DNA gene spacers and ITS rDNA sequences.
The results of a 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.
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. 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 several chloroplast (trnL
intron, trnS-trnG, psbB-psbF, atpB-rbcL) and nuclear gene (ITS2)
spacer sequences suggests a number of relationships, some of which
were inferred by previous morphological studies, some of which are
new. The sequences of Cycas 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 to Bowenia,
but does seem to have an affinity with Zamia and
Microcycas. Lepidozamia is more closely related to
Encephalartos than to Macrozamia. Sequence variation
among the species of Ceratozamia is low. Microcycas and
Zamia are closely related.
Key words: Cycadales, cycads, molecular systematics, phylogeny