Caerau Road Cutting ST135748

Every time I head into Cardiff on the western access road I tell myself, one day I must stop and look at the road cutting flora. The sparse vascular plant cover and abundant bryophytes on the eroding banks always looks promising. Yesterday I was nearby with a spare couple of hours, so I parked in Caerau and climbed over the fence.

For ref the BGS website shows the geology to be a combination of Blue Anchor Formation and Mercia Mudstone Group, these Triassic deposits exposed by the A4232 cutting. The lack of any top dressing has allowed an interesting assemblage of 26+ terricolous species to colonise. Hypnum cupressiforme var. lacunosum, Ctenidium molluscum (only on the S.E. side of the road) Fissidens adianthoides and Trichostomum crispulum were all abundant, with other frequent species noted including Aloina aloides, Dicranella varia, Didymodon acutus, Didymodon ferrugineus and Homalothecium lutescens.

Didymodon acutus

Didymodon ferrugineus

Didymodon ferrugineus

The central reservation and verge 'dirt zone' held locally abundant Didymodon australasiae and occasional Weissia controversa var. densifolia was noted under the crash barriers.

Didymodon australasiae

Sychryd scramble

On the 20th a climb up through the complex of boulders and falls along the Glamorgan side of the Sychryd boosted the totals for SN90D from 90 to 159 and SN90E from 41 to 106. Highlights from the limestone section included scattered colonies of Cololejeunea calcarea (photo 1 below), Neckera crispa (just one small tuft noted), Oxyrrhynchium schleicheri (one small colony), Rhynchostegiella teneriffae (sheets of it above water line, photo 2), Seligeria acutifolia (small amounts at 2 locations, photo 3), S. donniana (only 1 fruiting patch seen,, photo 4), Taxiphyllum wissgrillii (1 patch noted on a small embedded rock) & a little Dermatocarpon miniatum (photo 5).

A couple of logs in the higher acid section of the gorge supported species including Barbilophozia attenuata, Blepharostoma trichophyllum, Cephalozia catenulata (photo 1 below), Dicranodontium denudatum & Riccardia palmata, plus there were a couple of nice patches of Hymenophyllum tunbridgense half way up the valley side.

Of note for the wrong reason was a single 10cm x 10cm patch of Lophocolea semiteres established on the track as you walk down the north side of Dinas Rock.

Earlier in the day on the way up the Neath Valley, three lay-by stops along the A465 all showed that the putative Didymodon australasiae is a well established component of the verge dirt zone along this road. A little Ephemerum minutissimum was also collected and checked under microscope at one of the stops.

Didymodon cf. australasiae update

Didymodon cf. australasiae 'dirt zone' habitat

I've been back to Dafen and noted the putative Didymodon australasiae was locally frequent in the 'dirt zone' of the road verge, the population appearing in patches (some very extensive) for over 1 km of the A4138. Yesterday I pulled into the lay-by of the Loughor bypass section of the A484 (Glamorgan) and walked back to a suitable looking dirty verge at SS56359793. Sure enough there was a good scattering of the same taxon. To assist potential searches the following pointers and photos should help build a search image:

• Forms mid-dark green patches, darker than frequently associated Barbula spp. and lacks brownish tones of D. tophaceus and orange tones of D. fallax.
• Grows both as mono-specific turf and as occasional shoots mixed with other spp.
• Leaves spreading-patent, tapering, the tip sometimes appearing pinched towards to a moderately cuculate tip.
• Some plants have broader leaves and the pinched leaf tip is more evident, these may be younger plants?
• The strong nerve is very evident on the upper surface of the leaf in certain light.
• Contrary to my earlier comments the species does crisp up a bit when dry as shown below.

It seems reasonable to suspect this species might be frequent in and around the Swansea-Llanelli area and possibly further afield, so if folks can take the opportunity to check the dirt zone of our major roads it will be interesting to find out how widespread the taxon really is - hopefully further clarification of its identification will come in good time.

Image above showing a couple of shoots mixed in with D. tophaeceus, B. convoluta and P. hornschuchianum.

Stumped on the hard shoulder

Apologies for bringing this post to the top, but it's an intriguing taxon worth bringing attention to (additional text shown yellow). Using the key to North American Didymodon I was taken on a pretty unambiguous journey to australasiae, a taxon which appears to be recognised in other parts of Europe as well as North America. The last part of the key identifies the key characters separating this species from umbrosus, which even with my limited experience, really looks very different and distinctions are clear. Interestingly David Holyoak's comments on Cornish material indicates that both australasiae and umbrosus occur there, both even confirmed by DNA. Given all this information I'm confused as to why australasiae is not included on the British list.

For the record the following additional images show the extra characters referred to in the key i.e. the bistratose margin towards the leaf tip (NB the proximal 2/3 of the margin is unistratose), strongly papillose cells, quadrate adaxial cells (presenta long the full length of the costa).

As can be seen below, the habitat was very mundane, the species occurring as patches in the outermost zone of colonised dirt (arrowed white, although I think my specimen came from the area indicated by the yellow arrow SN53100107). Direct associates in my sample include Didymodon tophaceus, Barbula unguiculata and Bryum dichotomum. PS. Thanks for the earlier comments, which prompted further examination of my sample.

Maybe it's just because I've had a long day but this one has me stumped. It was growing in the gritty debris of a roadside near Dafen, Llanelli, the most frequent associates including Cochlearia danica, Barbula unguiculata, Plantago coronopus, etc. Help please!