Bryophytes usually grow as a colony (an assemblage of individual shoots), and the colony form often changes according to environmental conditions, especially water conditions. Sanionia uncinata (Hedw.) Loeske (=Drepanocladus uncinatus (Hedw.) Warnst.) has various habitats ranging from swampy ground to exposed dry ground in the polar tundra. In order to quantify the variations in the colony form of bryophyte due to water conditions, we examined the colony form and shoot morphology of S. uncinata growing in a fellfield and snowbed in the high arctic, Spitsbergen, Svalbard. The colony thickness of the fellfield type was significantly thinner than that of the snowbed type. The colony density (mg/cm^3) and the number of shoots per unit square of the colony surface (no./cm^2) were significantly higher or larger in the fellfield type than those in the snowbed type. The dense colony in the fellfield site appears to lead to strong resistance to evaporation from the colony surface. Frequency of branching in shoots from the fellfield type was higher than that from the snowbed type. The colony of the snowbed type was composed of many branchless shoots, while that of the fellfield type had few branchless shoots. Frequency of branching in the shoots from the snowbed type was lower in the upper part of shoot than in the lower part. However, frequency of branching in the shoots from the fellfield type did not significantly change according to the position of shoot. These results could explain why a dense colony is formed in the fellfield.

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Reexamination of the specimens on which the record of Jungermannia jenseniana Grolle from Japan was based, proved that they should be classified as Jungermannia sphaerocarpa Hook., and thus J. jenseniana is excluded from the hepatic flora of Japan.

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