A Small Piece of a Complicated Puzzle: The Resurrection of Randia tomatillo Loes. from the Randia aculeata L. Complex (Rubiaceae)

Within the Rubiaceae family, the genus Randia comprises approximately 90 species, with significant morphological diversity in growth forms, leaf shapes, and floral sexuality. In particular, Randia aculeata is a taxonomically challenging species distributed from the southern United States to South America and the Antilles that exhibits high morphological variability and ecological adaptability. One of its synonyms is Randia tomatillo, originally described from coastal dunes in Veracruz, Mexico, and it has been inconsistently described in the taxonomic literature either as a distinct species or as a synonym for R. aculeata. This study aimed to resolve the taxonomic identity of R. tomatillo through morphological observations from herbarium specimens, and transverse sections from mature leaves were observed using SEM microscopy to explore crystal types. Morphological traits, such as lifeform, twig pubescence, stipule persistence, fruit size, and pericarp texture, are critical in distinguishing R. tomatillo from morphologically related species, such as R. aculeata and Randia thurberi. Anatomical features, particularly the presence of prisms in the leaf mesophyll and epidermis, are unique to R. tomatillo, suggesting their diagnostic value. Ecological adaptations, such as scandent growth and spongy pericarps for hydrochorous fruit dispersal, further support its distinction as a species adapted to coastal environments. These findings highlight the need for a comprehensive taxonomic reassessment of Randia, integrating morphological, anatomical, and ecological evidence.