Rotundatin, a new 9,10-dihydrophenanthrene derivative was isolated from the orchid, Dendrobium rotundatum, which also afforded the known stilbenoids 2,7-dihydroxy-3,4,6-trimethoxyphenanthrene, 2,7-dihydroxy-3,4,6-trimethoxy-9,10-dihydrophenanthrene, nudol, moscatin and batatasin-III. Rotundatin was shown to be 2,5,9-trihydroxy-4-methoxy-9,10-dihydrophenanthrene from spectral and chemical evidence. © 1992.