Species relationships and phylogenetic diversity of the African genus Encephalartos Lehm. (Zamiaceae)

The African endemic cycad genus Encephalartos consists of 68 extant taxa, that are of great conservation concern as 85% are threatened (CR, EN, or VU) and four, are extinct in the wild (EW). Due to there being no formally published monographs for the genus, there is lack of consensus on taxonomically significant characters. This lack of clarity regarding the species relationships and access to several taxa have made researching this group challenging. Nevertheless, numerous studies have proven that this genus has low levels of genetic variation over a wide distribution. The aim of this study was to produce the most robust phylogenetic reconstruction of Encephalartos to date. This was done by using markers from three different genomes – plastid (rbcL, matK-trnK, trnH-psbA, cab), mitochondrial (nad1) and nuclear (26S, AGAMOUS, NEEDLY, nrITS1) – for all currently accepted taxa. The results obtained show an increase in resolution for both the backbone and species level relationships compared to previous work. This genus can be separated into five new geographic groups – northern African, central African, eastern African, Mozambican-Zimbabwean, and southern African. There is also an indication that the evolution of the southern African group is driven by a form of reproductive isolation. Further studies on this group should be approached systematically based on the foundation provided by the linages that are shown in this study.