Abstract
Eighteen components were isolated from the methanolic extract of leaves of Rhododendron formosanum Hemsl. (Ericaceae), an endemic species in Taiwan, and evaluated for their allelopathic properties. Of the isolated compounds, 3 β-friedelinol, 5,6β-epoxy-5β-stigmastan-3β-ol, 5,6α-epoxy-5α-stigmastan-3 β-ol, lupeol and ursolic acid revealed inhibitory effects at 10−4 M or above, whereas α-tocopherol, friedelin and β-amyrin acetate exhibited stimulatory effects on the radicle growth of the test plants at the same concentration or above. However, squalene and α-amyrin showed either a stimulatory or inhibitory effect. The remaining four components, coumarin, β-sitosterol, adian-5-en-3β-ol and 3β-acetoxyurs-12-en-28-al, were not significantly effective in the present bioassay, but have been reported as allelopathic agents elsewhere.