The primitive liverwort Haplomitrium hookeri, only twice recorded previously in Eastern North America in 1917 and 1956, is reported from north-facing rocks at 1300m in the Tuckerman Ravine on Mt Washington, New Hampshire. Its occurence here on vertical wet rocks associated with the liverworts Cephalozia bicuspidata, Scapania undulata and Solenostoma hyalinum and the mosses Blindia acuta, Philonotis fontana, Pohlia nutans, Racomitrium fasciculare and R. heterosticum is very different from its ecology elsewhere in the northern hemisphere. The plants were sterile but had extensive subterranean leafless fungus-containing axes. Future molecular analyses are expected to reveal that the endophyte in the Mt Washington plants is a member of the Mucoromycotina, the earliest fungal lineage known to form associations with land plants.