Reinstatement of Bulbophyllum quadrangulum (Orchidaceae) from B. chondriophorum with morphological and molecular evidence

The orchid species Bulbophyllum quadrangulum (Orchidaceae) was previously considered synonymous with B. chondriophorum. However, a thorough examination of the protologues and type specimens has revealed that B. quadrangulum is, in fact, distinct from B. chondriophorum. Its elongated, narrowly lanceolate lateral sepals (1.9–2.5 cm), with a caudate-acuminate apex, are quite different from the shorter, obliquely ovate and acute lateral sepals (7–8 mm) of B. chondriophorum. The two species do not overlap geographically and differ in flowering period and altitudinal range. Phylogenetic analyses based on plastid genome sequences also strongly support the independence of the two species. Consequently, this study reinstates the species status of B. quadrangulum and presents an updated morphological description, phenology, and distribution based on comprehensive information. Furthermore, the study also provides a distribution map, color photographs, detailed floral dissection, and habitat information.