Unveiling the identity of Viburnum laterale (Viburnaceae), a mysterious species disappeared nearly 100 years, based on morphological and molecular evidence

Viburnum laterale Rehder is a poorly known shrub endemic to southeastern China that has remained taxonomically enigmatic since its publication more than a century ago. The species was known only from a few historical collections that lacking critical characters, and no living populations had been documented for nearly a century. Here, we report the rediscovery of this taxon and clarify its taxonomic identity using integrative approach combining morphological and molecular evidence. Observations of living plants reveal several previously undocumented reproductive traits, including inflorescences with conspicuous white sterile marginal flowers, as well as fruit and seed morphology. Comparative analyses of living material, type specimens, and protologues indicate that V. laterale is most similar to V. hanceanum Maximowicz, differing mainly in its nearly glabrous indumentum, longer peduncles, and more coarsely serrate leaf margins. Phylogenetic analyses based on chloroplast coding sequences, together with an expanded dataset comprising nuclear ITS and three plastid markers (rbcL, matK, and ndhF), consistently place V. laterale within sect. Tomentosa (Maximowicz) Nakai, where it forms a strongly supported clade with V. hanceanum. Based on morphological and molecular evidence, V. laterale is transferred to sect. Tomentosa and treated as a variety of V. hanceanum, namely V. hanceanum var. depilatum M. Tang & L.C. Zhao. Our study resolves a long-standing taxonomic problem and highlights the importance of rediscovering historically enigmatic taxa for accurate species delimitation in Viburnum.