Build It and They Will Come (a year or two later.....)

I’ve had to build a few things on the farm here, and have experimented with various different roofing types. The thatched pig-sty, unsurprisingly, has yet to attract any passing spores of thatch moss, Leptodontium gemmascens, instead having a sparse cover of common epiphytes. The turf roofs are too grassy to have much more than a few tufts of Weissia controversa in barer patches. But where I’ve just thrown up an infertile substrate and pretty much left nature to do the rest, there is now a much more diverse range of bryophytes.

The latest barn has a section composed of old lime-mortar rubble, donated by a friend who was renovating a church. Two years on, it’s mostly dominated by common species such as Barbula unguiculata, Didymodon rigidulus and Cratoneuron filicinum, but there's some Pseudocrossidium revolutum and a little bit of Gyroweisia tenuis on a couple of lumps of mortar – this was on the walls of the church.

Lime-mortar rubble on roof of cattle barn

Another section was composed of mixed sand and gravel from Lawrence Landfill near Haverfordwest. They quarry sandstone blocks for building stone, and the ‘washings’ are heaped up in a huge pile and sold cheaply. It seemed to me to the nearest approximation to the heathland soil at Marloes where I was collecting plants from for our commercial green roofing projects.

Quarry at Lawrence Landfill, Haverfordwest

The quarry itself is interesting but largely bare – the owners let me poke about for an hour or two, and I found some Aloina aloides and Fossombronia incurva. Earlier this year, a surplus pile of the aggregate tipped near the barn sprouted 3 tiny shoots of an Aloina which, on close-inspection, proved to be one of the two rare tiny species, A. rigida or A. brevicollis. I suspected the former, but without capsules it couldn’t be proven. The shoots didn’t make it through the summer.

'Obtuse' leaf tips of the tiny Aloina shoot

It was pleasing then yesterday when I found a tiny Aloina patch with ripe capsules on the barn roof. The narrow cells on the basal leaf margins again proved that it was one of the two, but this time, the spore size of 12-16 microns was enough to confirm it as Aloina rigida. The 3-cell high membrane at the base of the peristome teeth is also a useful character pointing away from the common A. aloides. If I hadn’t found Aloina rigida at Castlemartin (and Pendine) earlier this year, this ‘species of principal importance for conservation’ would have been new to west Wales. Rather remarkably, when I went back the following day to take a photo, I found a larger Aloina patch nearby, which proved to be A. ambigua. This lacks the elongate basal cells, has a taller 3-5 cell membrane below the peristome teeth, and larger spores. It's Nationally Scarce, but known from the old sand quarry near Trefigin - I also found it on a building site in Johnston this year. Just for good measure, there's some Aloina aloides on the roof too - a nice hat-trick.

The basal marginal cells of the Aloina rigida - elongated, hyaline and thin-walled

Elsewhere on the roof, the early abundance of the weedy Leptobryum pyriforme is being subsumed by Dicranella varia and some typical calcifuge species such as Ceratodon purpureus and Polytrichum juniperinum. A few thalli of Riccia glauca have appeared on one edge. Some Pseudocrossidium hornschuchianum is currently sporting young capsules; not a common occurrence according to the books. The English stonecrop that I dotted about has yet to achieve much coverage, but maybe that’s no bad thing.

Pseudocrossidium hornschuchianum with young capsules

Aloina rigida location on barn roof