Thursday, 11 January 2018

Hinksey Heights Bryophytes

Botanists enjoying a coffee break in the wood along the valley
Sunday was another winter outing for local botanists, this time on the Hinksey Heights south of Oxford and better attended than the last. Hinksey is in vice county 22 (Berkshire) meaning a day off recording vascular plants for me, but the meeting was focused on bryophytes anyway. The main interest was one of a series of long narrow valleys draining north off the heights, fed by calcareous groundwater emanating from the limestone along the valley sides. There is peat in the upper part of the valley, and it was once an open fen rich in plants such as grass-of-Parnassus but now mostly covered in willow and reed.

The valley is a nature reserve and can be reached from the Hinksey Heights Golf Club via a footpath and board walk leading north-west from the car park (the temptation to botanise which was resisted). The valley opens out at the entrance near its bottom where there are fabulous views of Oxford and its encircling hills to the north and east. The southern slope here supported the only area of Juncus subnodulosus (blunt-flowered rush) fen we came across, but it was rather overgrown.

The stream tumbling over its tufa weirs
This is where we set to bryologising, and as there were a few new-comers to the subject we could share the revelation that is the tiny world of bryophytes, with ample demonstration material provided by the several common species growing on the accumulated fen litter. The only fen moss we found, however, was a scrap of Bryum pseudotriquetrum. The stream within the woodland in the valley bottom had me fantasising of Eucladium and Gymnostomum species, with its spectacular tufa weirs (or barrage tufa) and drifts of petrified leaves and twigs. Tufa is formed where limey waters precipitate calcite (the principle calcium carbonate mineral) onto lower plants and debris, encasing them in stone, and has a specialist bryophyte flora adapted to this highly alkaline environment. The bryophyte flora, however, was rather dull, most surfaces being covered in the pleurocarp Cratnoneuron filicinum, or the thallose liverworts Conocephalum conicum and Pellia endiviifolia. This suite of species followed us up the valley, dominating the weirs, dripping banks of the stream and springs.

The peaty springs higher up were a little richer, but mostly covered in wefts of the common mosses Plagiomnium affine and P. undulatum. Exceptionally, however, and the highlight of the meeting, both species were producing sporophytes, which for P. affine is a very rare occurrence. Most species of Plagiomnium are dioecious (sexes on separate plants) and are shy to produce sporophytes — the only currently known record of P. affine in fruit in Oxfordshire or Berkshire is from nearby Bagley Wood, found by Watson many decades ago.

Fruiting Plagiomnium affine growing with Cratoneuron filicinum in a tufa spring
Like the two Plagiomnium species, most of the mosses and liverworts we recorded were general calcareous woodland plants rather than specialists of wet woodland or fens. We recorded a number of epiphytes such as the increasingly common Orthotrichum pulchellum and O. stramineum, as well as the uncommon and Brachythecium salebrosum growing on an elder. Altogether we recorded 9 liverwort and 38 moss species, but with a few specimens yet to be examined this is not the final tally. Thanks to everyone for an enjoyable meeting!

Brachythecium salbrosum growing on elder (left). The meeting was too early for the pretty capsules of Orthotrichum stramineum (right, April, Blenheim Park) but old dry capsules are distinctively red-brown and flask-shaped.

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