Oxygen availability is one of the main factors affecting seed germination capacity. On floodplains, oxygen supply is seasonally restricted because of flooding events. Seed ecotypes are able to cope with total submergence to different extents, depending on the species and its position in a given environmental gradient. This investigation tested three provenances of common ash (Fraxinus excelsior L.), one from a lowland site and two from upland sites, for germination capacity and germination velocity under water. The final germination capacity of all provenances was unaffected, but the germination velocity was decreased for all provenances. The adaptational significance of these results is discussed.