Euphorbia balsamifera subsp. adenensis (Euphorbiaceae) new to Socotra and notes on its taxonomy

• Published in: Nordic journal of botany Vol. 2025; no. 9
• Main Authors: Thulin, Mats, Weber, Michael H., Mubarak, Sami Ali Mohammed
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.09.2025
• Subjects: Canary Islands; disjunct distribution; Yemen
• ISSN: 0107-055X; 1756-1051
• DOI: 10.1002/njb.04842

Euphorbia balsamifera Aiton has been treated since 1965 as a disjunct species with two subspecies, subsp. balsamifera in the Canary Islands (Spain) and adjacent parts of northwestern Africa, and subsp. adenensis (Deflers) P.R.O.Bally in southwestern Asia and northeastern tropical Africa. However, in 2021, E. adenensis Deflers was resurrected based mainly on molecular and morphological data. We now record this taxon (as E. balsamifera subsp. adenensis) for the first time from Socotra, where it grows as small trees. Only three plants were seen in the southwestern part of the island. We also discuss the claimed morphological differences between E. balsamifera and E. adenensis that mainly concern size and habit of the plants, leaf shape, degree of fusion of styles, and presence or absence of pubescence on ovaries and fruits. We show that none of these characters can be used for species distinction and suggest that the best way to handle the situation taxonomically is to continue to treat E. balsamifera as a widespread and variable species with two geographical subspecies.