Tortula

Introduction

The genus Tortula Hedw. represents one of the most complex and diverse genera in terms of morphological variation in the family Pottiaceae. It includes approximately 100 species in the world, distributed mainly in temperate areas of North Hemisphere.
Its taxonomic circumscription has been controversial during the last two centuries, and there has been no consensus about which species or even other genera should be included in it. The genus, as emended by Zander (1993), is characterized by stem with central strand and absence of sclerodermis and hyalodermis, colour KOH leaf reaction usually yellow, costa in cross-section with dorsal and ventral surface cells developed, with hydroids, band of ventral stereids absent and dorsal band of stereids well-differentiated, usually semicircular in shape.
With the exception of the Brotherus´s (1924) treatment, the genus Tortula has never been monographed or critically revised. Only regional treatments exists which have been included in diverse floras.