The herbarium collections of Odontoschisma denudation and O. sphagni from The Netherlands have been revised in connection with a study of the phenotypic variation and ecology of these species. In O. denudatum two natural modifications can be distinguished. Mod. pachyderma is more common and grows in young, open Erica-Calluna heath vegetation, on sandy ridges and rarely on tree trunks. Mod. mesoderma occurs in old, often N-exposed ( Erica-)Calluna heath vegetation on shaded substrates. O. sphagni is far more common than O. denudatum and morphologically less variable. It is a characteristic species of oligotrophic bogs and wet heath vegetation. Rarely O. sphagni grows on tree trunks or in rather dry heath vegetation together with O. denudatum mod. mesoderma. In these atypical habitats O. sphagni remains a distinct species, readily distinguished from O. denudatum by the absence of gemmae.