In September, 2018, a research team carried out a field investigation in open deciduous woodlands covered by lava outcrops in Makueni County, southern Kenya. During the investigation, a shrubby Euphorbia with densely stellate hairs on abaxial leave surface attracted authors’ attention. In the following trip, researchers revisited the same area, performed more careful observations on its morphological characters, and collected enough specimens for further study.   

Supervised by Prof. WANG Qingfeng and Prof. HU Guangwan, PhD student WEI Neng from Wuhan Botanical Garden carried out the study of comprehensive morphology and molecular phylogeny around this Euphorbia. After sufficient literature consultant, specimens examinations, detailed morphological comparisons, as well as robust phylogenetic support, this species was finally confirmed to be new to science. The entitled paper, “Euphorbia mbuinzauensis, a new succulent species in Kenya from the Synadenium group in Euphorbia sect. Monadenium (Euphorbiaceae)”, was published in the taxonomic journal Phytokeys.   

Species epithet, ‘mbuinzauensis’, is named for the type locality of the new species. Morphologically, Euphorbia mbuinzauensis is most similar to E. pseudomollis, but differs mainly by its shrubby habit (up to 4 m), abaxial leaves surfaces with densely stellate hairs, 2-4-forked cymes, smaller bracts (ca. 2.5 × 3.0 mm), smaller cyathia (6 mm wide), crimson glands without narrow smooth margin, smaller fruits (ca. 8 × 7 mm) and ovoid seeds (ca. 1.8 × 2.2 mm).  

Euphorbia mbuinzauensis is distinct from other species in Synadenium group with strong morphological and phylogenetic support. The previously segregated genus Synadenium is tested as monophyly, using phylogenetic inference based on a nrDNA dataset. Nevertheless, an expand and dense sampling of closely related species is needed to draw this conclusion with greater confidence. It is worth mentioning that the phylogenetic relationships among the species in Synadenium group exhibite extremely short branches, indicating that this lineage is likely to have radiated very recently.   

According to the IUCN criteria, the new species is assessed as “Endangered status”, given the very limited populations and individuals in the wild. There is urgent need to take actions including in situ and ex situ conservation, to protect this fragile and lovely succulent plant.    

Morphological features of Euphorbia mbuinzauensis (Image by WEI Neng) 

The maximum likelihood tree inferred from the complete nuclear ribosomal DNA sequences (Image by WEI Neng)