Cytochalasin H is a cell-permeable fungal toxin used in actin polymerization studies and cytological research. Isolated from the solid fermentate of Phomopsis theicola, an endophytic fungus isolated from the leaves of an endemic Formosan plant Litsea hypophaea Hayata. It is also a progesterone receptor antagonist. Cytochalasin H is a cell-permeable fungal toxin used in actin polymerization studies and cytological research. Isolated from the solid fermentate of Phomopsis theicola, an endophytic fungus isolated from the leaves of an endemic Formosan plant Litsea hypophaea Hayata. It is also a progesterone receptor antagonist.