Morphology, anatomy and phylogeny of the two sister halophytic genera Microcnemum and Arthrocnemum (Salicornioideae/Amaranthaceae)

The intensive study of the genera Microcnemum and Arthrocnemum based on their morphological and anatomical characteristics and their phylogenetic relationships has led to a notable advance in the knowledge of both taxa, almost two centuries after their publication. Morphology and anatomy were analyzed using optical (OM) and scanning (SEM) and transmission (TEM) electron microscopy techniques. Phylogenetic reconstruction was done by Bayesian inference through the ITS molecular marker. For the first time, a phylogeny is presented focused exclusively on both halophyte genera, showing a separation between the two species of Arthrocnemum described for the Mediterranean territory (Arthrocnemum meridionale and Arthrocnemum macrostachyum). In Microcnemum, the redefinition of its floral formula is noteworthy mainly after the first observation of individual hermaphrodite and proterandrous flowers in each cyme, in contrast to the structure established by previous authors. A micromorphological pattern was also discovered in the exotesta for each species: smooth in Microcnemum coralloides, slightly striated in A. meridionale and strongly striated and granular in A. macrostachyum.