Summary The liverwort Riccia fluitans exists in two forms, a submerged living waterform and a landform with characteristic morphological differences. When treated with abscisic acid (ABA) the waterform converts into the landform. When the thallus of the submerged waterform is exposed to an agar surface or moist filter paper formation of the landform is induced and endogenous ABA is increased after a lag period of 2–3 hours by a factor of 10–30, although osmotic potential of the cell sap is only slightly affected. After Long-term exposure the ABA concentration in the landform is still higher by a factor of 2. While mineral deficiency and salt stress have no effect on the formation of terrestrial structures in the thallus of Riccia fluitans, excess of ammonium, nitrate or phosphate induces the landform, but no short-term increase of endogenous ABA can be observed.