In southern African savannas, geoxylic suffrutices or ‘underground trees’ attain only a hundredth to a tenth the height of normal trees, but other traits have received little attention. Geoxylic suffrutices and congeneric trees were compared for minimum and maximum values of seven morphological traits. Thirty-six geoxyle-tree pairs co-occurring in Katanga (Democratic Republic of the Congo) were compared, based on data from standard floras. The tree/geoxyle ratio ranged from 0.92 to 1.67 and was greater than 1 in 12 of 14 trait comparisons. However, the difference was significant in only five comparisons. Reproductive traits generally did not differ. The maximal value of leaf traits (lamina length, lamina width, petiole length) was 33–67% greater in trees. The morphological traits of geoxyles are not much altered compared with their tree counterparts, especially for reproductive traits. For vegetative traits, geoxyles express a restricted part of the phenetic space of trees, being unable to attain trait values as high as those of their tree congeners. However, unlike bonsais or alpine dwarfs, the leaves of geoxyles are not much smaller compared with normal trees.