Identification notes
This southern rarity is a warmth-demanding species and the majority of its recent populations are not far from the sea. So, if you are bryologising in dry calcareous ground in maritime areas and find a Weissia with a long seta and a capsule that has a thin membrane across its mouth in lieu of a peristome, there’s just a chance it could be W. condensa rather than W. brachycarpa, which is similar.
Spray up the leaves and take a look at the nerve – it’s really stout in W. condensa. The only other similar species with such a wide nerve is W. controversa var. crispata, but that has peristome teeth, of course.
A word of warning – the capsules have to be at just the right stage of maturity for unequivocal identification. Like most Weissia species, you’ll normally have to wait until spring before the capsule lids fall. Then, the membrane across the mouth is intact for only a short time before it starts to disintegrate. So, if the capsules are a bit over-mature, it may not be possible to see the membrane at all, although if you slice off the capsule mouth and mount it on a slide you might be able to make out some tattered remnants. There’s a good example this in the photo gallery below.