Five go to Colonsay

Lochan on Colonsay: spot the botanist!
Image: K. Walker

The two members of BSBI's Science Team (Head of Science Kevin Walker and Scientific Officer Pete Stroh) have been working incredibly hard writing scientific papers, preparing Species Accounts and of course seeing their book Threatened Plants in Britain and Ireland through to publication. 

They certainly deserved a break, but of course for botanists a break means... going out looking at plants! Read on to hear Kevin's account of his and Pete's latest botanical adventure: 

"Botanising on Colonsay is always an adventure and this June was no exception for the “famous five” botanists who assembled in Oban on the 16th June: myself, Pete Stroh, David Pearman, Simon Leach and Stephen Bungard standing in for Owen Mountford who has been a regular team member but went earlier this year to take part in the Colonsay Spring Festival. This was our fifth successive trip to record the flora of the island for a new Flora to update the checklists produced by McNeill (1910) and Clarke & Clarke (1991).

David Pearman on Colonsay
Image: K. Walker

"Colonsay is small by Hebridean standards; nine miles long and four miles at its widest. It actually comprises two islands: Oransay, the smaller of the two and reputedly the landing place for St Columb before he settled in Iona, is connected to the “mainland” by a wide sandy bay (The Strand) which is walkable at low tide. The geology is uniformly acid with a few bands of limestone that outcrop in a few places (e.g. Kiloran Bay). 

"It is low-lying (the highest point is 143 m) with a rugged terrain covered in deep heather and bogs contrasting with large expanses of tightly grazed machair on the dunes and where sand has been blown inland. The coastline is mainly rocky, with some impressive cliffs with large seabird colonies, and fragments of saltmarsh in less exposed locations. 

Ajuga pyramidalis
Image: K. Walker

"There are about a dozen lochans, the largest of which (East, West and Middle Loch Fada) support an internationally important aquatic flora due to its populations of Slender Naiad (Najas flexilis). It is largely unwooded although two ancient woods survive on its east coast, the largest (Coille Mhor) supporting a remarkable diversity of hyperoceanic vascular plants, lichens, bryophytes and ferns.

"Despite its small size Colonsay is a haven for wildlife. Although most famous for its breeding bird populations which include Chough, Hen Harrier, Golden Eagle, and Corncrake (Jardine et al., 2017) its flora is equally impressive. Since 2014 we have recorded nearly 700 species with an average of around 171 species per monad, despite the fact that many coastal monads only have a small area of land. 

"Although Colonsay has a number of rarities such as Irish Lady’s-tresses (Spiranthes romanzoffiana), Slender Naiad (Najas flexilis), Pyramidal Bugle (Ajuga pyramidalis) and Dune Gentian (Gentianella uliginosa), it is the abundance of the supporting cast that really grabs the attention. 

Utricularia stygia
Image: K. Walker

"For us “southerners” these include Hay Scented Buckler Fern (Dryopteris aemula) which is ubiquitous in shaded habitats, often growing with Lesser Twayblade (Neottia cordata) and Wilson’s Filmy-fern (Hymenophyllum wilsonii) whereas numerous bog-pools support a distinctive assemblage including Slender Sedge (Carex lasiocarpa), Bog Sedge (C. limosa), Great Sundew (Drosera anglica), White-beaked Sedge (Rynchospora alba) and Nordic Bladderwort (Utricularia stygia) and more locally Oblong-leaved Sundew (Drosera intermedia) and Bog Orchid (Hammarbya paludosa) (a third site in 2018). 

"Flushes abound with Dioecious Sedge (Carex dioica) and Pale Butterwort (Pinguicula lusitanica) and in 2015 we found Broad-leaved Cottongrass (Eriophorum latifolium) new to the island in a small valley mire on the east coast. 

"Around the coast Saltmarsh Flat-sedge (Blysmus rufus) is almost guaranteed in reasonably sized saltmarshes whereas Scots Lovage (Ligusticum scoticum) and Roseroot (Sedum rosea) are locally abundant on seacliffs and rocky shores. 

Euphrasia sp. - you'll need the
Eyebright Handbook to
work out which one!
Image: K. Walker

"The edges of rough tracks are “festooned” (that maybe overstating it!) with Chaffweed (Centunculus minimus) and All-seed (Radiola linoides) and less occasionally Chamomile (Chamaemelum nobile). 

"Hay meadows abound with Hay-rattle (Rhinanthus minor) and Euphrasia arctica whereas E. nemorosa is widespread and E. confusa, E. tetraquetra and E. micrantha more localised in coastal habitats and heaths. “Northerners” may be surprised by the abundance of Bugloss (Anchusa arvensis), Scarlet Pimpernel (Anagallis arvensis), and Blunt-flowered Rush (Juncus subnodulosus) and the occurrence of Marsh Helleborine (Epipactis palustris) which still occurs in the coastal marsh where it was discovered in 1906 (Somerville, 1907).

"Colonsay also has a large non-native element, largely due to plantings in the policy wood at Colonsay House and Gardens, the centre of the main estate on the island. Notable escapes include Rhododendron (Rhododendron ponticum), which is well naturalised on moorland and bogs across the island, American skunk-cabbage (Lysichiton americanus) and Pink Purslane (Claytonia sibirica). Species regenerating prolifically in the policy woods themselves include New Zealand Privet (Griselinia littoralis) and Chilean Myrtle (Luma apiculata).

Elatine hexandra
Image: K. Walker

"Although we’ve visited 79 of the 81 monads that make up the island, we continue to make new discoveries. This year’s star finds were Six-stamened Waterwort (Elatine hexandra) in East Loch Fada where it has been known since the 1980s, Drosera x obovata growing amongst its parents near to Loch Cholla, Wood Avens (Geum urbanum) in the woods near Colonsay house and Gardens and Greater Chickweed (Stellaria neglecta) in a 100 year-old plantation near to Scalasaig. 

"But possibly the most remarkable find was Meadow Thistle (Cirsium dissectum). This was originally noticed by David Jardine in 2017 and confirmed by us after a chance encounter between the botany and bird teams. This appears to be the most northerly location in Britain, and just to the north of populations in similar habitats on Islay and in Knapdale.

Kevin and David on Colonsay,
testing the new Eyebright Handbook
Image: P. Stroh

"But many species have yet to be re-discovered; most notably Potamogeton x prussicus (P. alpinus x P. perfoliatus) recorded by Heslop-Harrison (1948) in 1940 and only ever recorded from one other site in Britain and Rock Samphire (Crithmum maritimum) first recorded by Alex Somerville along with Marsh Helleborine (Epipactis palustris) in 1906 (Somerville, 1907).

"As well as recording for the Flora we also tested out the new BSBI Euphrasia handbook, which helped us to more tentatively differentiate between Euphrasia confusa, E. nemorosa and E. arctica, although boundaries between these three species appear to merge on Colonsay! 

Kevin's NPMS plot on Colonsay
Image: K. Walker

"I also spent half a day recording my National Plant Monitoring Scheme (NPMS) square in the SW of the island which was set up in 2015 with single plots in five habitats – loch margin, acid mire, dry heath, saltmarsh and rocky shore. No significant changes as yet but fascinating to see the subtle shifts in composition and structure from year to year. 

"One of our group has developed a particular interest in plant galls.  Prior to our visits the only gall recorded for the island was of a rust, Puccinia magnusiana, on Creeping Buttercup (Ranunculus repens). This year we added eleven galls to the 53 recorded in the previous three years. Highlights included galls of sawflies Euura auritae on Eared Willow (Salix aurita) and E. weiffenbachii on Creeping Willow (Salix repens). As you’d expect, midge galls also feature prominently, although some species common on the mainland seem to be rare here, e.g. Dasineura urticae on Stinging Nettle (Urtica dioica), which we have so far found in only two places, despite the host plant being pretty widely distributed around the island. Another striking midge gall we were particularly pleased to find was that of Contarinia tiliarum on Lime (Tilia sp.) trees in the estate woodlands around Colonsay House. 

Drosera intermedia on Colonsay
Image: K. Walker

"Last but not least, Pittosporum species/cultivars planted in the gardens around Colonsay House have galls of Trioza vitrioradiata; this psyllid gall was first recorded in Britain in 1993, in Cornwall, and has since been spreading north and east. We were surprised to find it on Colonsay, at what must be the very northern limit of its current distribution in the UK.

"We also saw a few new birds (for us) on the island, including a pair of Whinchat and an Iceland Gull which was feeding on the carcass of a 70 ft Sei Whale that had been washed up on Kiloran beach in December.

"All in all we had another fantastic week on this Hebridean gem of an island – it is always sad to leave but this year our spirits were raised by a pod of Minke Whales breaching not far from the ferry; our first in five trips and well worth the wait! Next year we plan to see basking sharks…maybe…

References

Clarke & Clarke 1991. The Flowering Plants of Colonsay and Oransay. Privately published.

Heslop-Harrison, J.W. 1948. Potamogetons in the Scottish Western Isles, with some remarks on the general natural history of the species. Transactions of the Botanical Society of Edinburgh 35, 1-25.

Jardine, D.C., Peacock, M.A. & Fisher, I.A. 2017. The Birds of Colonsay and Oransay. The Argyll Bird Club, Lochgilphead.

McNeill, M. 1910. Colonsay. One of the Hebrides. David Douglas, Edinburgh.

Somerville, A. 1907. On the occurrence of the Rock Samphire (Crithmum maritimum L.) and the Marsh Helleborine (Epipactis palustris Crantz) on the west coast of Scotland.