O. minuta Thunb. var. callosa Salter was included in section Sagittatae of the genus Oxalis L., based on superficial morphological resemblance to O. minuta var. minuta. We questioned this placement due to the reticulate pollen grains displayed by this taxon, whereas members of section Sagittatae have rugulate-reticulate pollen grains. A lack of good herbarium and living specimens prohibited a better taxonomic placement of this taxon. Living plants were recently found in the Pakhuis Pass (Western Cape, South Africa), which enabled this re-assessment of its taxonomic affinities. A suite of morphological and palynological characters were identified that differ significantly from both the typical variety and all other members presently included in section Sagittatae. These include the ovate to elliptic anthers, the orientation of long and mid-level reproductive organs, the absence of an indumentum on the leaves, the presence of calli on the leaflets, sepals and petals, reticulately deposited epicuticular wax on the leaves, the broadly funnel-shaped corolla tube and the basally fused anthers. We therefore raise Oxalis minuta var. callosa to specific rank as O. hygrophila Dreyer, and transfer it from section Sagittatae to section Latifoliolatae.
Kumwenda, M., Dreyer, L. L., & Marais, E. M. (2004). A taxonomic reassessment of the varieties of Oxalis minute (Oxalidaceae) and the change of O. minuta var. callosa to specific rank as O. hygrophila. South African Journal of Botany, 70(2), 259–264. https://doi.org/10.1016/S0254-6299(15)30244-1