Phylogenetic relationships and evolution of extant horsetails, Equisetum, based on chloroplast DNA sequence data (rbcL and trnL-F)
Abstract
Equisetum is a small and morphologically distinct genus with a rich fossil record.
Two subgenera have been recognized based principally on stomatal position and stem
branching: subg. Equisetum (eight species; superficial stomates; stems branched) and
subg. Hippochaete (seven species; sunken stomates; stems generally unbranched). Prior
attempts at understanding Equisetum systematics, phylogeny, and character evolution
have been hampered by the high degree of morphological plasticity in the genus as
well as by frequent hybridization among members within each subgenus. We present the
first explicit phylogenetic study of Equisetum, including all 15 species and two samples
of one widespread hybrid, Equisetum x ferrissii, based on a combined analysis of two
chloroplast markers, rbcL and trnL-F. Our robustly supported phylogeny identifies
two monophyletic clades corresponding to the two subgenera recognized by earlier workers.
The phylogenetic placement of Equisetum bogotense, however, is ambiguous. In maximum
likelihood analyses, it allies with subg. Hippochaete as the most basal member, while
maximum parsimony places it as sister to the rest of the genus. A consensus phylogeny
from the two analyses is presented as a basal trichotomy (E. bogotense, subg. Hippochaete,
subg. Equisetum), and morphological character evolution is discussed. We detected
rate heterogeneity in the rbcL locus between the two subgenera that can be attributed
to an increased rate of nucleotide substitution (transversions) in subg. Hippochaete.
We calculated molecular-based age estimates using the penalized likelihood approach,
which accounts for rate heterogeneity and does not assume a molecular clock. The Equisetum
crown group appears to have diversified in the early Cenozoic, whereas the Equisetaceae
total group is estimated to have a Paleozoic origin. These molecular-based age estimates
are in remarkable agreement with current interpretations of the fossil record.
Type
Journal articleSubject
Science & TechnologyLife Sciences & Biomedicine
Plant Sciences
divergence times
Equisetum
fossil record
horsetails
likelihood ratio test
molecular clock
morphological character evolution
penalized likelihood
phylogeny
CLOSEST LIVING RELATIVES
SUBGENUS EQUISETUM
SEXUAL-BEHAVIOR
REPRODUCTIVE-BIOLOGY
LIKELIHOOD APPROACH
DIVERGENCE TIMES
GENUS EQUISETUM
SEED PLANTS
GAMETOPHYTES
ORIGIN
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https://hdl.handle.net/10161/21862Published Version (Please cite this version)
10.1086/376817Publication Info
Des Marais, DL; Smith, AR; Britton, DM; & Pryer, KM (2003). Phylogenetic relationships and evolution of extant horsetails, Equisetum, based on
chloroplast DNA sequence data (rbcL and trnL-F). International Journal of Plant Sciences, 164(5). pp. 737-751. 10.1086/376817. Retrieved from https://hdl.handle.net/10161/21862.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Kathleen M. Pryer
Professor of Biology

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