Three Sphagna from two sites and three sections gave an opportunity to get out the books and learn to love Sphagnum. Not quite there yet, but they are kind of attractive and they can't be that difficult, can they?
The BBS field guide operates on four groups, which Smith says there could be 11 and Frey says the molecular data supports not more than 4. In terms of field ID though as long as the groupings get you to a species I don't mind arguing about the rest later.
Now I've started to get a feel for them I'll have to seek out some more to play with
S.palustre - section Sphagnum
Hooded branch leaves get you into the section and it's a pretty closed group. It also has a fat stem cortex but you don't necessarily need to see that. S.palustre is a common one and a big blousy affair, with fat branches and of course hooded leaves. This one was picked up in woodland and with pretty catholic tastes this seems like the most likely one to find in that environment. The capiltula is darker than the surrounding branches.
S.capillifolium - section Acutifolia
This section has a rosy pin-red tint (pigment anthocyanin) which is detectable with alkaline. I applied some KOH to the leaves to get a blue reaction here. A slender species with a red stem, S.capillifolium also has the centre of the capitulum a deep red and deeper than its edges. A paler centre sends you in another direction.
S.denticulatum - section Subsecunda
This is the section of bendy branches, and in this case at least a bendy capitulum too. denticulatum is a common bog moss and likes ditches. Once you get into the section by the manifest bendiness of it all (English name "cow horn bog moss"!) this species is separated from its buddies by having particularly pointed (lanceolate) branch leaves.
Sphagnum: A Field Guide, Hill, M.O.
Mosses and Liverworts of Britain and Ireland: A Field Guide, Atherton,D.M & Bosanquet,S.D.S.
The Liverworts, Mosses and Ferns of Europe, Frey,W & Frahm,J-P (trans. T.Blockeel)
The Moss Flora of Britain and Ireland, Smith,A. J. E. & Smith,R