New plant growth regulators, named myxostiolide (1), myxostiol (2), and clavatoic acid (3), have been isolated from Myxotrichum stipitatum, and their structures have been established by spectroscopic methods including 2D NMR. The biological activities of 1, 2, and 3 have been examined using tea pollen and lettuce seedling bioassay methods. With tea pollen, compound 1 inhibited the pollen tube growth to 14% of control at a concentration of 100 mg/L. With lettuce seedlings, compound 2 accelerated the root growth from 1 mg/L to 100 mg/L and compound 3 inhibited the root growth, to 52% of control, at a concentration of 100 mg/L.
