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Phylogenetic relationships and evolution of extant horsetails, Equisetum, based on chloroplast DNA sequence data (rbcL and trnL-F)

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Date
2003-01-01
Authors
Des Marais, DL
Smith, AR
Britton, DM
Pryer, KM
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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 article
Subject
Science & Technology
Life 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
Permalink
https://hdl.handle.net/10161/21862
Published Version (Please cite this version)
10.1086/376817
Publication 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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Scholars@Duke

Pryer

Kathleen M. Pryer

Professor of Biology
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