F. L. Anderson and S. G. Knees, “STUDIES IN THE FLORA OF ARABIA: XXXII. VACHELLIA PENNIVENIA (LEGUMINOSAE: MIMOSOIDEAE) – A LITTLE-KNOWN TREE SPECIES ENDEMIC TO THE ISLAND OF SOCOTRA”, Edinburgh J. Bot., vol. 76, no. 3, pp. 313–318, May 2019, doi: 10.1017/S0960428619000076.