Sirindhomia, a new orchid genus from Southeast Asia

The new orchid genus Sirindhomia , named after H. R. H. Princess Maha Chakri Sirindhorn of Thailand, is established to accommodate three species from Thailand (Chiang Mai and Tak provinces), Myanmar (Shan State), and China (Yunnan province). Two new species are described and a new combination, based on Habenaria monophylla Collett & Hemsl., is made; all of the three species are illustrated, and a distribution map is provided. Sirindhomia belongs to subtribe Orchidinae and has an overall similarity with Ponerorchis, Hemipilia , and Amitostigma. However, it significantly differs in its column morphology which is more reminiscent of that found in the vegetatively distinct genus Orchis. The new species, Sirindhomia pulchella and S. mirabilis , seem to be local endemics, as they are only known from the Thai mountains Doi Chiang Dao and Khao Hua Mot, respectively. Sirindhomia monophylla , on the other hand, is known from a very large part of the range of the genus. All Sirindhomia species known are restricted to limestone mountains at 800–2200 m alt., mainly growing in rock crevices and among scrub as well as on grassy slopes. They flower from April to June.