CHAW, SHU-MIAW1*, TERRENCE W. WALTERS2, SHARON S. HU1, and HSIN-HSIAO CHEN1. 1Institute of Botany, Academia Sinica, Taipei, TAIWAN; 2Montgomery Botanical Center, Miami, Florida. - Phylogeny of extant Cycadales inferred from chloroplast matK gene.
Cycadales, the cycad order, has approximately 185 extant species in
eleven genera and three families (Cycadaceae, Stangeriaceae and
Zamiaceae) (Jones 1993). Cycads are confined to the tropical and
subtropical regions of both hemispheres. They were shown to be the
basal-most clade of living gymnosperms based on multiple gene analyses
(Chaw et al. 2000; Bowe et al. 2000), but relationship of their
families and genera are not completely known. In this report
chloroplast matK gene is used to infer the phylogeny among the genera
and higher taxa of cycads. Ginkgo is employed as the outgroup.
Analysis using either the nonsynonymous sites or the first two
position of matK gene identifies Cycas as the basal-most group
of cycads, Stangeria as the next basal, and the rest genera
form a well supported group, in which three subfamilies, Bowenioideae,
Encephalartoideae, and Zamioideae as defined by Stevenson (1992), are
each resolved as monophyletic. Traditionally the latter two
subfamilies constitute the family Zamaiaceae, which, howevevr, is not
sustained by the matk data. In contrast to morphological and
cytological studies, our data do not support inclusion of
Bowenia in the family Stangeriaceae. In addition,
Lepidozamia is shown to be sister to Encephalartos
rather than to Macrozamia. The nonsynonymous sites of matK gene
in cycads (except Lepidozamia) have evolved in a relatively
clock-like manner.
Key words: Cycadaceae, Cycadales, evolution rate, Phylogeny, Stangeriaceae, Zamiaceae