Caroxylon rising

Mucina, Ladislav, 2017, Caroxylon (Chenopodiaceae s. str.) in continental southern Africa and Madagascar: a preliminary nomenclatural synopsis and biogeographical considerations, Phytotaxa 312 (2), pp. 151-178 : 152

Caroxylon rising again

The wide diversity of life forms in Salsola sensu lato [annual, creeping and dwarf to high semi-succulent shrubs and even small trees— S. arborea C.A.Sm. ex Aellen (1963: 117) ], variable pollen morphology ( Toderich et al. 2000, 2010, Toderich 2008) and discovery of marked physiological variability involving several carbon assimilation syndromes ( Voznesenskaya et al. 1999, 2013, Pyankov et al. 2001b, Kadereit et al. 2003) were clear indicators of the non-monophyletic origin (and hence taxonomic heterogeneity) of the genus Salsola in its original or later traditional circumscriptions. The molecular phylogenetic study by Pyankov et al. (2001a) and Kadereit et al. (2003) provided further support to these observations. Pyankov et al. (2001a) revealed two main lineages in the tribe Salsoleae , having NAD-ME and NADP-ME C 4 photosynthesis, respectively with Caroxylon belonging invariably to the former syndrome (see also Sage et al. 2011). These two photosynthetic syndromes corroborated two sets of C 4 photosynthesis types in leaves and different structural and photosynthetic characteristics in cotyledons.

Kadereit et al. (2003) established that Salsola comprises two monophyletic groups, which were unformally named Salsola I and Salsola II. The molecular studies by Akhani et al. (2007) and Wen et al. (2010) went further and showed, beyond any doubt, that both nuclear and chloroplast markers render Salsola s.l. polyphyletic. Akhani et al. (2007) suggested resurrecting Caroxylon , and placed this genus, together with its sister clade ” Kaviria ” [including Kaviria Akhani & E.H.Roalson (2007: 948) , Halocharis Moquin-Tandon (1849: 201) , and Nanophyton Less. (1834 − 1835: 197)], within the new tribe − Caroxyleae (originally published as ” Caroxyloneae ”, but corrected in Akhani et al. (2014). A number of nomenclatural adjustments in Caroxylon taxa were made by Akhani et al. (2007) accordingly, and more combinations followed (e.g. Brullo et al. 2013, Akhani et al. 2016). Wen et al. (2010) confirmed the findings of Akhani et al. (2007), suggesting the monophyly of both Caroxylon and the tribe Caroxyleae . Studies of Feodorova (2011, 2012, Feodorova & Samigullin 2015) further demonstrated that the South African Caroxylon species of the sections Caroxylon and Tetragonae formed well-supported clades (in both MP and Bayesian analyses). Feodorova & Samigullin (2015), using rather limited sequenced material, suggested that at least some Northern Hemisphere taxa of Caroxylon might belong to different genera (see also Hernández-Ledesma et al. 2015). In a further step, they transferred 32 taxa of Salsola and Caroxylon (as defined by Akhani et al. 2007), all from the Northern Hemisphere, to Nitrosalsola Tzvelev (1993: 80) , which originally included only N. nitraria Tzvelev (1993: 80) . Their new combinations have not been effectively published in the mentioned online article; these were formally validated later by Feodorova (2015). Since these taxonomic changes do not concern the monophyletic southern African clade, we shall refrain here from discussing the merits of the proposed redefinition of Nitrosalsola .