Macro- and micromorphology reveal four entities in the highly variable Oxalis polymorpha Mart. ex Zucc. (Oxalidaceae)

Leaf morphoanatomy can provide useful information for the taxonomy of morphologically similar species or the recognition of infraspecific taxa. Here, we evaluated the taxonomic utility of leaf morphological and anatomical characters for the recognition of distinct morphologies currently placed under Oxalis polymorpha Mart. ex Zucc., a highly polymorphic species of Oxalis from the Brazilian Atlantic Forest. We analyzed leaves of 13 specimens gathered from five populations throughout the species' geographic distribution. Leaf samples were analyzed under light and scanning electron microscopy. We observed differences in the leaf blade venation patterns, in the indumentum of petioles and leaf blades, in the pulvinar vascular tissue configuration, and in the midrib tissue organization. The variation in these characters allowed us to recognize four different morphotypes among these samples. These morphotypes are geographically disjunct and differ among each other in additional morphological features, such as leaf arrangement along the stem, leaflet shape, inflorescence position, petal color, and fruit shape. Oxalis polymorpha is a good candidate for investigating if phylogenetic relationships support recognition of each of its morphotypes at the species level.