Racomitrium lanuginosum (Hedw.) Brid.


Racomitrium lanuginosum is most commonly found on exposed rock surfaces and boulders. Patches of this species can also be seen growing with Racomitrium elongatum on gravel on the roof of the UBC Biological Sciences Building.

In the photo to the left, R. lanuginosum is growing in a bog.





Overall Structure:

Racomitrium lanuginosum is an acrocarpous moss that grows in hoary grayish-green to whitish-green mats.




Shoots are irregulary-pinnately branched. The conspicuous, whitish awns are rather flexuouse when dry.






Leaf Structure:

The leaves are a linear-lanceolate shape. The presence of a broadly decurrent, hyaline awn with strongly dentate margins makes recognition of this species relatively straightforward.




A cross-section of the distal part of a leaf reveals that sharp papillae are confined to the hyaline marginal areas which correspond to the decurrent strips of the awn. Also note that the lamina is wholly unistratose while the costa is bistratose.



The costa extends beyond the leaf apex into the awn.



The leaf cells are variously short-rectangular to elongate, with thick, sinuose walls.




The hyaline awn is decurrent, with sharp papillae and large, multicellular teeth.






Racomitrium lanuginosum sporophytes, youngOverall, sporophytes are uncommon but may be abundant in coastal areas.






Racomitrium lanuginosum, sporangia with calyptraeYoung sporangia are capped by  mitrate calyptrae. Note the fringe of lobes radiating from the calyptrae bases.






Racomitrium lanuginosum sporangium, young, with operculumright: a young sporangium minus calyptra








Racomitrium lanuginosum sporangium, oldleft: an old sporangium that has lost its operculum










The seta is twisted near the base of the sporangium. It moves hygroscopically to aid with spore dispersal.