Reinstatement of Thyrsacanthus Moric. (Acanthaceae) and taxonomic novelties in the genus

Abstract

Phylogenetic studies based on molecular data indicated that the Neotropical genus Anisacanthus Nees (Acanthaceae), as traditionally circumscribed, is not monophyletic. Based on the priority of the description of Thyrsacanthus ramosissimus Moric. versus the description of Thyrsacanthus Nees, we are reinstating the name Thyrsacanthus (Art. 42.1 of the ICBN) to include the South American species traditionally assigned to Anisacanthus. Drejera Nees is included in the synonymy of Thyrsacanthus, a new species (T. microphyllus A. Côrtes & Rapini) is described, three new combinations are proposed, two new taxonomic synonyms at the species level indicated and three lectotypes designated. The positions of Anisacanthus trilobus Lindau and A. pohlii Lindau are uncertain, requiring further investigations.

The Tetramerium lineage (Acanthaceae: Justicieae) does not support the Pleistocene Arc hypothesis for South American seasonally dry forests

“…The main clades recovered in our study generally agree with those in Daniel et al (2008). The primary difference is that among the South American species three (vs. one) clades are recovered here and new generic circumscriptions are needed to establish monophylesis for Schaueria ( sensu Nees, 1847), Pachystachys ( sensu Wasshausen, 1986), and Thyrsacanthus ( sensu Côrtes et al, 2010). These lineages are morphologically distinct and geographically structured between dry and moist forest biomes.…”

“…Species distributions were obtained from herbarium collections and literature (Wasshausen, 1986; Hilsenbeck, 1989; Ezcurra, 1994; Smick, 2004; Côrtes et al, 2010). For a definition of phytogeographic areas, georeferenced data were plotted on a map of ecoregions (Olson et al, 2001; available at: http://www.worldwildlife.org/science/data/terreco.cfm).…”

“…1). Each genus, as traditionally circumscribed, is essentially restricted to a single biome and has a relatively low number (< 20) of species (Nees, 1847; Wasshausen, 1986; Smick, 2004; Côrtes et al, 2010). Pachystachys , Streblacanthus , and Fittonia are almost exclusively distributed in lowland regions of the Amazon basin [excluding Streblacanthus monospermus Kuntze, which diverges close to the root of the Tetramerium lineage and does not pertain to this group (Daniel et al, 2008), and Streblacanthus cordatus Lindau, which occurs in the moist lowlands to the west of the Andes and in southern Central America].…”

“…Schaueria is endemic to the Atlantic forest (Bahia state, in Brazil, to southern South America), while Thyrsacanthus usually occurs in dry forests and restingas [coastal lowlands formed by Quaternary sandy sediments (Silva, 1999)], in northern (Venezuela and Guyana), northeastern (Bahia, Piauí, and Rio Grande do Norte states, in Brazil) and southwestern South America (Bolivia). The lineage does not contain any characteristic savanna species, but Thyrsacanthus ramosus (Nees) A. Côrtes & Rapini occurs in dry forests at the interface of the Cerrado and Atlantic forest domains (Goiás and São Paulo states, in Brazil) (Nees, 1847; Wasshausen, 1986; Smick, 2004; Daniel et al, 2008; Côrtes et al, 2010; Côrtes, personal observation).…”

“…Phylogenetic studies (Daniel et al, 2008) contributed to generic recircumscription within the Tetramerium lineage (Côrtes et al, 2010) and showed that colonization in Mexico ( Mirandea clade) probably proceeded diversification of the lineage in South America. However, none of the analyses to date adequately sampled the diversity of the South American clade.…”