Taxonomic reappraisal of Henckelia hookeri and H. collegii-sancti-thomasii (Gesneriaceae): two little-known endemic species of the Eastern Himalaya in India

Summary Henckelia hookeri (C.B.Clarke) D.J.Middleton & Mich.Möller and H. collegii-sancti-thomasii A.Joe, D.Borah, Taram & Sandhya are two lesser-known, narrow endemic species occurring in the eastern Himalaya of Arunachal Pradesh in India. In this study, the correct taxonomic identity of H. hookeri is discussed, and second-step lectotypification for its basionym, Chirita hookeri C.B.Clarke is carried out. Henckelia collegii-sancti-thomasii, a recent synonym of H. hookeri, is reinstated based on morphological and molecular evidence. The present study represents the first detailed documentation of H. hookeri . Taxonomic descriptions, colour photographs and a distributional map are provided for H. hookeri and H. collegii-sancti-thomasii . A table comparing significant morphological differences between H. hookeri , H. collegii-sancti-thomasii and their allied species, and a key to the species occurring in the Indian Himalayas and northeast India are also provided.