Globally, Euphorbiaceae Juss. comprises about 330 genera and 6,300 species, with new genera continuously being added through taxonomic revisions substantiated by molecular phylogenetic studies (Cheek et al., 2016) and recently discovered novelties (Athiê-Souza et al., 2015; Zhou et al., 2017). Generally, members of the Euphorbiaceae are found in tropical climates characterized by warm, humid environments. However, some species grow in subtropical and temperate regions with mild winters and hot summers. The highest diversity is observed in the tropical areas of Africa, and the Americas, with notable hotspots in Madagascar, Central and South America, and Southeast Asia.

In Bhutan, the Euphorbiaceae was reported to comprise 29 genera and 82 species, according to the works of Grierson and Long (1987). These include Euphorbia L. (12); Pedilanthus Poiteau (1), Bridelia Willd. (5), Phyllanthus L. (11), Flueggea Willd. (1), Glochidion J.R.Forst. & G.Forst. (8), Breynia J.R.Forst. & G.Forst. (1), Sauropus Blume (3), Drypetes Vahl (2), Aporosa Blume (1), Antidesma L. (3), Baccaurea Lour. (1), Jatropha L. (2), Croton L. (5), Codiaeum Jussieu (1), Manihot Millier (1), Ostodes Blume (1), Claoxylon Jussieu (1), Mercurialis L. (1), Acalypha L. (3), Alchornea Swartz (2), Trewia L. (1), Mallotus Loureiro (4), Cleidion Blume (1), Macaranga Petit-Thouars (2), Homonoia Loureiro (1), Ricinus L. (1), Baliospermum Blume (3), and Sapium Browne (3). However, due to taxonomic revisions, many species names have been synonymized, and several names have been reclassified based on molecular phylogenetic studies (Wurdack et al., 2004, 2005; Hoffmann et al., 2006; Tokuoka, 2007). The heterogeneity, circumscription, classification, and affinities of the Euphorbiaceae have long been controversial (Tokuoka, 2007), and an attempt to dismember the family and species has been proposed (Webster, 1987). For example, the genus Antidesma L., Aporosa Blume, Baccaurea Lour., Bridelia Willd., Breynia J. R. Forst. & G. Forst., Flueggea Willd., Glochidion J. R. Forst. & G. Forst. Phyllanthus L. historically placed under Euphorbiaceae, has been reclassified to the Phyllanthaceae. At the same time, Drypetes Vahl is moved to Putranjivaceae due to plastid rbcl DNA analysis (Wurdack et al., 2004), which are listed (Table 1). This reclassification includes 32 and 2 species from Phyllanthaceae and Putranjivaceae respectively, which were reported by Grierson and Long (1987) within the Euphorbiaceae. Considering these taxonomic advancements, Bhutan has 17 genera, and 40 species under the Euphorbiaceae, with accepted names ascertained through the online databases such as World Flora Online (WFO), Plants of the World Online, and the Global Biodiversity Information Facility. Acalypha spiciflora Burm.f. (synonym: Cleidion spiciflorum (Burm.f.) Merr.) is currently unresolved name in Plants of the World Online and has been excluded from the species list (Table 1).

The classification within the Euphorbiaceae has undergone significant revisions, as illustrated by the reclassification of Sumbaviopsis J. J. Sm. This monotypic genus was described by Johannes Jacobus Smith in 1910, a Dutch botanist, based on specimens from the Indonesian archipelago. The genus Sumbaviopsis is derived from the genus Sumbavia Baill., which was named after the island of Sumbawa in Indonesia. The suffix “-opsis” means “resembling,” reflecting its similarity to Sumbavia. Initially, species were described under the genus Sumbavia: S. rottleroides Baill. in 1858 and later S. macrophylla Müll. Arg. in 1864 (Shaw, 1960). After its initial description, Sumbaviopsis albicans was classified under several different genera, including Rottlera, Croton, and Cephalocroton, before Smith established it under Sumbaviopsis. Additionally, Müller-Argoviensis independently described it as Coelodiscus speciosus Müll.Arg. in 1865 (Muller, 1866). However, S. rottleroides was later found to be antedated by Doryxylon Zoll., with the correct name being Doryxylon spinosum Zoll., restricted distribution in Philippines, Java, Bima, and Sumbawa. Doryxylon and Sumbaviopsis can be subsumed into one genus by Balakrishnan (1967). Further, a close examination of preserved material at Kew determined that S. macrophylla is the same species as S. albicans, which was first described by Blume in 1825 and provisionally placed in the genus Adisca Blume (Shaw, 1960; Welzen, 1999). The study of Sumbaviopsis is complicated by the rarity of mature flowers in collected specimens, leading to an incomplete understanding of its unique reproductive structures and variability in features such as the torus, leaf shape, and fruit morphology (Welzen, 1999). The species Sumbaviopsis albicans has not been recorded in Bhutan, despite similar climatic conditions existing in the southern belt of the country. This highlights a gap in Bhutan’s botanical records. This research aims to establish a database for Sumbaviopsis albicans in Bhutan, addressing this gap and contributing to the understanding of this species. By documenting this species for the first time in Bhutan, the study will update the floristic records and provide insights into the distribution and ecological significance of Sumbaviopsis.

During a field visit to the subtropical belts of Bhutan by the Nature Guide and Professional Forester, the species was observed along the feeder road connecting Panbang and Mothanguri in the Zhemgang District. Specimens were collected, and photographs of different plant parts were taken to examine morphometric traits. The herbarium specimens were collected and maintained as per the guidelines of Jain and Rao (1977), Woodland (1997), and Thiers (2017). Photographic images and herbarium specimens were later examined using a digital floral database including World Flora Online, Plants of the World Online, and the Global Biodiversity Information Facility. The species morphometric characters were validated using related articles by various authors (Welzen, 1999; Wurdack, 2004; Kathriarachchi et al., 2005; Huaxing and Gilbert, 2008) and compared with regional floral databases such as the eFloras of India, China, and Thailand. This analysis confirmed that the species is Sumbaviopsis albicans, which had not previously been recorded in the flora of Bhutan.