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Fifty species of flowering plants new to the mainland of Yemen are reported from field trips undertaken in 1992, 1995 and 1998. The species roughly fall into three ecological groups, (1) species from the coastal zone of Hadramaut and Mahrah regions, (2) species from the escarpment mountains and plateau in Hadramaut and adjacent areas, and (3) species from the monsoon woodlands of eastern Mahrah close to the Oman border. The species in group (1) were previously mostly believed to be endemics either of Oman or Somalia. Most of the species in group (2) are previously known front Oman and/or Somalia, and sometimes also from eastern Ethiopia and beyond. The largest group is group (3), with species from the "Dhofar fog oasis". The fog moisture here supports a woodland that is denser than anywhere else in Yemen. This vegetation is well known in the Dhofar region in Oman, but in Yemen it has remained practically unknown up to now. Many of the species in this group ha e previously been regarded as endemics of the Dhofar region of Oman, but some of them have more or less wide distributions in tropical Asia or in north-eastern tropical Africa.