Bryophytes of Dorchester (Oxfordshire)

Three bryologists met at Dorchester Abbey (SU5794) on a grey, drizzling morning for the fifth excursion of the season. The Abbey graveyard and buildings proved to have a lot to offer, with a grand total of 41 species, pipping our previous season's best churchyard at Bletchingdon (36 species). Probably the top find was Gyroweisia tenuis on the east facing walls of the Abbey. Gyroweisia can be easily confused with other species, particularly Leptobarbula berica, and the Sussex Bryological Group have an excellent blog on this topic.

Gyroweisia tenuis habitat (with Porella platyphylla in foreground)

The other nice find in the churchyard was Syntrichia papillosa. This is a species that appears to be spreading in lowland Britain, possibly helped by eutrophication of a range of substrates from various sources of nitrogen (e.g. NOx from car exhausts). On the other hand, it may be that the species is just recovering from losses during an earlier period of substrate acidification from SO2 pollution (and the loss of hedgerow elms). For example, Eustace Jones notes that Herbert Napier (recording in Oxon. 1909-1914) reported it as "not uncommon" and suggested that the species had increased since the time of Boswell (recording in Oxon. 1858-1897). Jones himself reported S. papillosa as "certainly rare" (this would have applied to the 1935-1953 period) and describes the species as typically only found in single locations within sites (and gives hedgerow trees, "usually elm", as the habitat). Perhaps at this point the species was still widespread but locally rare, meaning that it was often overlooked during surveys. Certainly it appears to have subsequently declined, as it was only recorded twice in Oxon. in the period 1953-1991 (Jones, 1991).

At Dorchester we found nice stands of the plant on a tombstone, but also on the slats of a park bench, suggesting a novel mode of gemmae movement! See the two pictures of the photogenic S. papillosa below:


The full list from Dorchester Abbey appears below:

Amblystegium serpens	Grimmia pulvinata	Rhynchostegium confertum
Barbula convoluta var. convoluta	Gyroweisia tenuis	Rhynchostegium murale
Barbula unguiculata	Homalothecium sericeum	Rhytidiadelphus squarrosus
Brachythecium rutabulum	Hypnum cupressiforme	Schistidium crassipilum
Bryum argenteum	Hypnum cupressiforme var. lacunosum	Syntrichia latifolia
Bryum capillare	Kindbergia praelonga	Syntrichia montana
Bryum rubens	Orthotrichum anomalum	Syntrichia papillosa
Calliergonella cuspidata	Orthotrichum cupulatum	Zygodon viridissimus var. viridissimus
Didymodon fallax	Orthotrichum diaphanum	Lophocolea bidentata
Didymodon insulanus	Oxyrrhynchium hians	Lunularia cruciata
Didymodon luridus	Phascum cuspidatum	Porella platyphylla
Didymodon nicholsonii	Plagiomnium rostratum
Didymodon sinuosus	Pseudocrossidium hornschuchianum
Didymodon vinealis	Pseudoscleropodium purum
Fissidens taxifolius var. taxifolius	Rhynchostegiella tenella

After lunch we walked a circuit through the Dyke Hills (SU5793) west of Dorchester, and then followed the Thames anti-clockwise back to the town.

The (flooded) Dyke Hills in winter.

The Dyke Hills are an Iron Age earthwork, and covered in a slightly improved form of calcareous grassland, the hills themselves presumably being formed from river gravels excavated locally. The bryophyte flora reflects this. After some time searching, we came up with the following, fairly meagre, list:

Weissia species	Homalothecium lutescens
Barbula unguiculata	Oxyrrhynchium hians
Brachythecium rutabulum	Phascum cuspidatum
Bryum rubens	Plagiomnium affine
Fissidens dubius	Pseudoscleropodium purum

The riverside circuit turned up several expected riverside bryophytes, including Syntrichia latifolia, Cinclidotus fontinaloides, and Dialytrichia mucronata, whilst the close inspection of a multi-stemmed willow in the floodplain of the River Thame at SU580937 yielded an impressive 15 epiphytes on one tree, including more S. latifolia and S. papillosa.