Juniper haircap moss is a botanical citizen of the world, occurring on every single major continent (including Antarctica!). Haircap mosses are so named because of the fibrous covering which protects the developing sporophyte from water loss. In botanical terms, the haircap would be known as a hairy calyptra, and is present within most genera of the group. When the sporangium matures and the spores are ready to be released, the calyptra falls off so that the spores can be dispersed unimpeded. To see what the mature sporangium looks like underneath the hairy calyptra, scroll down to the last four photographs on this page for the closely related Polytrichum commune.

Some of the other images on that page show cross-sections of the Polytrichum stem. Unlike most other mosses, members of the subclass Polytrichidae have tissue specialized for the transport of water and nutrients (the hydromes and leptomes), analogous to what can be found in ferns, gymnosperms and flowering plants. The presence of conducting tissue allows this group of mosses to be relatively large compared to other mosses, and indeed, the tallest known moss, Dawsonia superba of New Zealand, can grow to a height of 50cm. I haven't been able to find an online image that illustrates the size of Dawsonia superba, but you can get an idea by checking out Dawsonia grandifolia (image number 7) on this page with plants from New Guinea, though I only estimate the height of those mosses to be 20cm or so.

Botany / photography resource link: Epimediums via Darrell Probst, Epimedium guru. If you're interested in reading more about Darrell, check out this interview from Fine Gardening magazine.