Guwahati: A small flowering plant growing beside a perennial stream in Arunachal Pradesh’s Upper Siang district has turned out to be a species new to science, adding to the rich but still incompletely documented plant diversity of the Eastern Himalaya.
Named Begonia siangensis, the plant was discovered during a floristic exploration of the Siang River basin in 2024. Researchers found it in a shaded habitat between Bomdo and Jengging, at an elevation of around 600 metres.
The discovery has been formally described in the Edinburgh Journal of Botany.
The species belongs to the section Platycentrum, a group of begonias that is particularly diverse in Northeast India. Although it resembles the previously known Begonia iridescens, researchers identified several characteristics that distinguish it from its close relative.
The plant has a creeping stem that can grow up to 35 cm long, with thickened nodes that produce roots. Its dark green leaves are asymmetrical, while their undersides have small, oval projections that give them a corrugated appearance.
Its pink flowers provide another distinguishing feature. The female flowers droop, and the wings of the ovary are nearly equal in size and extend down towards the flower stalk.
These characteristics, taken together, helped establish that the plant represents a distinct species.
A closer look at the plant
The researchers, S. Kishwan, T. U. Thackeray and N. V. Page of the Thackeray Wildlife Foundation, compared the collected specimens with Begonia species recorded from India, Myanmar and China.
The examination included published descriptions, taxonomic keys and specimens held in several herbaria. The team also consulted digital collections and botanical databases before concluding that the plant had not previously been described.
The new species is most closely related to Begonia iridescens, which is also known from the Siang region and Myanmar.
However, the differences are significant. Unlike B. iridescens, which has conspicuous silver spots between the veins and blue iridescence on its leaves, B. siangensis has unvariegated leaves.
The new species also has less hairy flower stalks and nearly equal ovary wings. In B. iridescens, the wings are distinctly unequal, with the lower wing considerably longer than the two lateral ones.
The researchers have provided photographs, illustrations and a comparative table in the paper to help distinguish the two species.
The specimens collected during the study have been deposited in herbaria at the Botanical Survey of India, the Forest Research Institute and the Wildlife Institute of India.
A species known from just one location
The plant was found growing alongside other moisture- and shade-loving species, including Elatostema, Henckelia oblongifolia, Leptoboea and Selaginella.
For now, Begonia siangensis is known only from Upper Siang district, between Bomdo and Jengging.
Its restricted known distribution raises questions about how widely the species occurs in the region. However, the researchers have cautioned against drawing conclusions about its conservation status based on the limited information available.
The paper provisionally classifies the species as Data Deficient under the International Union for Conservation of Nature (IUCN) framework.
The researchers have called for systematic surveys of shaded, perennial stream habitats between 500 and 1,000 metres in the Upper Siang Valley to establish whether additional populations exist.
Such surveys would help determine the species’ actual distribution, population size and potential conservation requirements.
Arunachal’s botanical diversity
The discovery adds to the growing number of Begonia species documented in Arunachal Pradesh, which has one of the highest concentrations of the genus in India.
The paper notes that around 100 Begonia species and 13 varieties have been recorded in India, distributed across 11 sections. Northeast India is particularly diverse, with the Platycentrum section accounting for 55 species and nine varieties.
Arunachal Pradesh alone has 58 Begonia species and six varieties described across four sections.
The genus remains an active area of botanical research, with new species continuing to be described from tropical and subtropical regions. Researchers have attributed this to the high degree of endemism in Begonia and the lack of adequate documentation in species-rich areas.
The discovery of Begonia siangensis highlights the importance of field exploration in the Eastern Himalaya, where small, specialised plants growing in streamside and forest habitats can remain undocumented despite the region’s botanical significance.
For the researchers, the next step is to establish whether the plant is confined to the location where it was found or occurs more widely across the Siang Valley.
Until then, the newly described begonia remains a species whose known range is limited to a single location, with its broader distribution and conservation needs yet to be established.