A MONOGRAPH OF THE GENUS MUELLERIELLA DUSÉN

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  A worldwide study indicates that the genus Muelleriella (Musci, Orthotrichaceae) consists of four species and one subspecies. The genus is indigenous to the subantarctic and south temperate regions of the Southern Hemisphere, and considered most closely related to Orthotrichum. Two species new to science, M. aucklandica Vitt and M. engelii Vitt are described and M. crassifolia subsp. acuta (C.M.) Vitt is recognized as distinct. A population study, utilizing several morphological characteristics of M. crassifolia, shows that this circum-subantarctic species consists of three intergrading, yet distinct populations, centering around Tierra del Fuego, the Australasian subantarctic islands, and Kerguelen Island. It is hypothesized that from this variable, widespread, lowland species, at least three species endemic to particular subantarctic islands have arisen, these tending to occur at higher elevations.