New begonia species found in Arunachal's Siang valley

Botanists have described a new species of wild begonia from the Siang river basin in Arunachal Pradesh and named it Begonia siangensis after the valley where it grows, the science news portal Research Matters reported.

The plant was found in 2024 by researchers from the Thackeray Wildlife Foundation in Mumbai during field surveys in Upper Siang district. It was growing beside a shaded mountain stream at about 600 metres above sea level, between Bomdo and Jengging.

How it was confirmed as new

The team collected both living plants and dried herbarium specimens. They compared them with records held in major herbaria in India and abroad, and checked digital collections from China and Myanmar, where many related begonias grow. The comparison showed the plant had not been described before.

Begonia siangensis is a creeping herb with pale pink flowers. It belongs to the Platycentrum group of begonias and looks most like Begonia iridescens, another species from the region. The two can be told apart by their leaves: B. iridescens has a bluish sheen and large silver spots, while the new species has plain dark green leaves. The underside of its leaves carries tiny blister-like bumps that give it a rough, ridged feel.

Other differences include drooping female flowers, flower stalks that are smooth or only lightly hairy, and a three-winged ovary in which the wings are almost equal in size. Its male flowers have a lopsided cluster of bright yellow stamens that point upward.

Known from one stream

So far the species has been recorded only from a single stream-side patch, growing with other plants that need constant moisture. Because its population size and range are unknown, the researchers have provisionally listed it as Data Deficient under IUCN guidelines.

They have called for focused surveys between 500 and 1,000 metres in the Siang valley to find out how widespread it is. The Siang basin lies in the Eastern Himalaya biodiversity hotspot, and Arunachal Pradesh has produced a steady run of new plant and animal records in recent years. The researchers say the find shows how much of the state's river valleys remains unexplored, and how much depends on protecting those habitats.