Molecular phylogeny of horsetails (Equisetum) including chloroplast atpB sequences

Abstract

Equisetum is a genus of 15 extant species that are the sole surviving representatives of the class Sphenopsida. The generally accepted taxonomy of Equisetum recognizes two subgenera: Equisetum and Hippochaete. Two recent phylogenetical studies have independently questioned the monophyly of subgenus Equisetum. Here, I use original (atpB) and published (rbcL, trnL-trnF, rps4) sequence data to investigate the phylogeny of the genus. Analyses of atpB sequences give an unusual topology, with E. bogotense branching within Hippochaete. A Bayesian analysis based on all available sequences yields a tree with increased resolution, favoring the sister relationships of E. bogotense with subgenus Hippochaete.

Reconstruction and Phylogenetic Significance of a NewEquisetumLinnaeus Species from the Lower Jurassic of Cerro Bayo (Chubut Province, Argentina)

“…Molecular phylogenetic analyses recovered the monophyly of the Hippochaete clade, but not that of the Equisetum clade (Des Marais et al, 2003;Guillon, 2004Guillon, , 2007 due largely to the inconsistent placement of Equisetum bogotense Kunth, 1815 in different studies (see Guillon, 2007 and references therein).…”

“…The two modern Equisetum subgenera -Equisetum and Hippochaete-have been historically distinguished based on numerous morphological features (Hauke, 1963(Hauke, , 1978Des Marais et al, 2003). However, their morphological differentiation has been recently questioned on the basis of molecular phylogenetic inferences (Des Marais et al, 2003;Guillon, 2004Guillon, , 2007. In these studies, Equisetum bogotense, a species classically assigned to the subgenus Equisetum based on morphological features, has been recovered as basal to subgenus Hippochaete (Guillon, 2007) or sister to both subgenera (Des Marais et al, 2003;Guillon, 2004 the genus (see Guillon, 2007).…”

“…However, their morphological differentiation has been recently questioned on the basis of molecular phylogenetic inferences (Des Marais et al, 2003;Guillon, 2004Guillon, , 2007. In these studies, Equisetum bogotense, a species classically assigned to the subgenus Equisetum based on morphological features, has been recovered as basal to subgenus Hippochaete (Guillon, 2007) or sister to both subgenera (Des Marais et al, 2003;Guillon, 2004 the genus (see Guillon, 2007). Nonetheless, the fossil record indicates that modern representatives of Equisetum constitute only a minute sample of its past diversity (Boureau, 1964;Stewart and Rothwell, 1993;Taylor et al, 2009) and therefore conclusions on character evolution exclusively based on extant species may be poorly supported.…”

Horsetails Are Ancient Polyploids: Evidence from Equisetum giganteum

“…Despite its limited number of species, its plasticity and survival through multiple geological time scales and extinction events render Equisetum a very successful lineage (Rothwell, 1996). The relationships between the different horsetail species is now well resolved with Equisetum bogotense basal to both the subgenera Hippochaete and Equisetum that each contain seven species (Guillon, 2004(Guillon, , 2007, while the Equisetopsida are most likely sister to both the whisk ferns (Psilotales) and ophioglossoid ferns (Ophioglossales; Grewe et al, 2013). Both molecular dating studies (Des Marais et al, 2003;Pryer et al, 2004) and fossil evidence (Stewart and Rothwell, 1993) indicate that extant horsetails diverged in the Early Cenozoic, not long after the Cretaceous-Paleogene (K-Pg) boundary ;66 mya.…”

The ultrastructure of epidermal surface of stem internods of horsetails of subgenus Hippochaete (Equisetum, Equisetaceae)

“…Важной особенностью является интенсивная гибридизация внутри каж-дой из двух групп и отсутствие достоверно вы-явленных гибридов между видами из Equisetum и Hippochaete, что также является одним из до-казательств их самостоятельности. Разделение на эти группы подтверждается и молекулярными исследованиями (Des Marais et al, 2003;Guillon, 2004Guillon, , 2007.…”