Tavistock. Report from the Botany Section

Tavistock nestles in the Tavy valley on the west side of Dartmoor so has a mild wet climate. Interesting habitats in the area include old walls and railway lines in the town, the Dartmoor commons of Whitchurch, Plaster, West and Buckland Downs, the wooded Tavy, Tamar and Walkham valleys and of course the tors, bogs and moorland of Dartmoor.

Hawkweeds (Hieracium) are a group of yellow-flowered perennials in the Daisy family. There are 411 microspecies in Great Britain, 35 in Devon and 10 in the Tavistock area. They are often very restricted in distribution, often endemic and difficult to identify. Tavistock is the home to two that occur nowhere else in Britain. These are the Nipple-toothed hawkweed (Hieracium monstrosum) and the Tavistock hawkweed (Hieracium medium). Both were originally introductions, probably via the railway and are found on a few old walls near the old railways in the town. They both have purple spotted leaves. Other hawkweeds are frequently found on old walls in the town and on dry banks.

Another common plant on walls is the little Fairy foxglove (Erinus alpinus), an introduction, with purple flowers; Tavistock has the best population in Devon.

The very rare Diaphanous Bladder-fern (Cystopteris diaphana) occurs in some abundance on dripping wet rock in the old railway cutting west of the viaduct over Bannawell Street and further down the line. These are the only sites in Devon although there are a couple in Cornwall. Another rare fern the Lanceolate spleenwort (Asplenium obovatum) is quite common on south-west facing old granite walls on the edge of Dartmoor.

Another rarity largely restricted in Devon to the south-west of Dartmoor is the little Cornish moneywort (Sibthorpia europaea), which is locally found on damp shaded walls and banks.

The Tamar valley is home to another introduced plant, Purple toothwort, (Lathraea clandestina) which is parasitic on willows and poplars and is found in flower in spring near rivers. A good site is at Morwellham. Wild daffodils (Narcissus pseudonarcissus) give a splendid show in places at Endsleigh in March.

Dartmoor tors are home to both Tunbridge and Wilson’s filmy ferns (Hymenophyllum tunbridgense and Wilsonii). Wilson’s is largely confined to tors such as Great Mis Tor whereas Tunbridge filmy fern is also found in woods such as in the upper Walkham valley. They are found in damp shaded crevices on tors and in deep clitter.

Fir clubmoss (Huperzia selago), another member of the fern family on the edge of its range on Dartmoor is found on ledges on many tors such as Leeden and Great Mis Tors near Tavistock.

The south-west Dartmoor commons occur on the metamorphic aureole around the edge of the Dartmoor granite and are generally heavily grazed which favours certain plants including the nationally scarce and declining Chamomile (Chamaemelum nobile) and the little Birdsfoot (Ornithopus perpusillus). The commons are a mosaic of dry acid grassland, with scrub, some poorly developed heath and wetter areas with some valley mires. The mire on Whitchurch Down is a good example with White-beak sedge (Rhynchospora alba), Ivy-leaved bellflower (Wahlenbergia hederacea), Pale butterwort (Pinguicula lusitanica), Lesser skullcap (Scutellaria minor) and both Round and Oblong-leaved sundews (Drosera rotundifolia and intermedia). The most remarkable plant on this site was the Irish Lady’s-tresses (Spiranthes romanzoffiana) found in 1957 but not seen since 1994. The nearest sites are in western Ireland and the Inner Hebrides, so why this plant should have been found in Devon remains a botanical mystery.

The Lesser butterfly orchid (Platanthera bifolia) is probably commoner on Buckland down than anywhere else in Devon and the Greater butterfly orchid (Platanthera chlorantha) gives a splendid display in Horndon churchyard.

Lastly Creason wood near Hillbridge has one of the few sites for Water Avens (Geum rivale) in Devon as well as Bog asphodel (Narthecium ossifragum), Royal fern (Osmunda regalis), Heath-spotted orchids (Dactylorhiza maculata), and eleven species of sedge.

Bob Hodgson