The Families and Genera of Cycads: A Molecular Phylogenetic Analysis of Cycadophyta Based on Nuclear and Plastid DNA Sequences

Abstract

A phylogenetic analysis of cycad genera was conducted using sequences of plastid rbcL (coding), trnL‐F (largely noncoding) regions, nuclear internal transcribed spacers (ITS), and part of the adjacent 26S rDNA gene. Trees were constructed from each region separately and a combined data set. The combined analysis yielded greater resolution but with a consensus tree that was not completely consistent with any published morphological studies or recent taxonomic classifications. The analysis supports a tree topology of (Cycas (Stangeria (Dioon (Bowenia (Macrozamia (Lepidozamia, Encephalartos)))), (Ceratozamia (Microcycas, Zamia)))). This topology implies inclusion of Epicycas in Cycas and Chigua in Zamia. Cycas is a distant sister to the remaining cycads, which form a coherent natural group, supporting recognition of two higher taxonomic groups.