On the hybrid origin of the C2 Salsola divaricata agg. (Amaranthaceae) from C3 and C4 parental lineages

<p>C₂ photosynthesis is characterized by recapturing photorespiratory CO₂ by RuBisCO in Kranz-like cells and is therefore physiologically intermediate between C₃ and C₄ photosynthesis. C₂ can be interpreted as an evolutionary precursor of C₄ and/or as the result of hybridization between a C₃ and C₄ lineage.</p> <p>We compared the expression of photosynthetic traits among populations of the <em>Salsola divaricata </em>agg. (C₂) from humid subtropical to arid habitats on the coasts of the Canary Islands and Morocco and subjected them to salt and drought treatments. We screened for enhanced C₄-like expression of traits related to habitat or treatment. We estimated species trees with a transcriptome dataset of Salsoleae and explored patterns of gene tree discordance. With phylogenetic networks and hybridization analyses we tested for hybrid origin of the <em>Salsola divaricata </em>agg.</p> <p>We observed distinct independent variation of photosynthetic traits within and among populations and no clear evidence for selection towards C₄-like trait expression in more stressful habitats or treatments. We found reticulation and gene tree incongruence in Salsoleae supporting a putative hybrid origin of the <em>Salsola divaricata </em>agg.</p> <p>C₂ photosynthesis in the <em>Salsola divaricata </em>agg. combines traits inherited from its C₃ and C₄ parental lineages and seems evolutionarily stable, possibly well adapted to a wide climatic amplitude.</p>