Andreaeobryum macrosporum (Andreaeobryopsida) in Russia, with additional data on its morphology

Andreaeobryum macrosporum is newly found in Yakutia, in the Sette-Daban Mountain Range, ca. 3000 km west of its known localities in Alaska. This is the first record of the genus and the class Andreaeobryopsida outside of North America. The species was found on calcareous rock outcrops, above the tree line in the Pinus pumila altitudinal belt. The morphology of the Siberian plants is described, focusing particularly on characters less studied in previous observations. Among these are: (1) axillary hairs with a complicated beak structure, apparently regulating mucilage exudation; (2) anacrogyny and the ability to substitute half of a leaf with an archegonium; (3) specific and relatively long sporophyte development within the epigonium, which is filled with mucilage mixed with macerated cells from the inner wall of the epigonium; (4) foot formed by cells with numerous chloroplasts, with inflated surface cells, sometimes forming finger-like protrusions and with the labyrinth ingrowth in 1–3 layers of the foot surface cells and also labyrinth structures on the surface cell wall facing placental space, whereas gametophyte cells have no ingrowth; (5) lobate archesporial tissue, not fully overarching the columella, which has membranaceous connectives between its segments and reaches the poorly differentiated outer spore sac, being thus similar to Andreaea in many respects; (6) flattened seta, which is not due to drying but lacking radial symmetry from the outset; (7) spore walls lacking or almost lacking an exine. It seems that Andreaeobryum plant possesses an ability to concentrate light, as the physiologically important parts of the structure, the haustorial part of the foot, the urn base, the archegoniophores and the meristematic zones near leaf bases, look considerably brighter in comparison with other parts of the plant.