Diapensia
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| Diapensia lapponica L. |
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Diapensia Diapensia lapponica is a plant in the family Diapensiaceae. It is a circumpolar arctic-alpine species which grows on exposed rocky ridges that are kept free from snow by high winds (Tiffany 1972).
It is a small cushion-forming evergreen perennial shrub, up to 15 cm in height. It has oval blunt leathery toothless leaves, up to 1 cm long, which are arranged in dense rosettes. It bears solitary white flowers, on stems up to 3 cm tall.
Day and Scott (1985), studying the plant in Newfoundland, discovered that it could be aged by counting growth-rings, and on this basis, many Canadian plants live to over a century old.
Two subspecies are recognised:
- Diapensia lapponica subsp. lapponica in eastern North America, Greenland, Scotland, Scandinavia, and western Arctic Russia
- Diapensia lapponica subsp. obovata in eastern Arctic Russia, Korea, Japan, Alaska and the Yukon
[edit] Status in Britain
In Britain, Diapensia is found only at a single site, Sgurr an Utha (grid reference NM889838), in the Glenfinnan Hills in southwest Invernessshire, the species' most southerly site in Europe. Here, the species occurs on acidic soil among stones on the ridge between the summit of Sgurr an Utha and the adjoining hill called Fraoch-bheinn, at 760 to 780 metres above sea-level. Its total extent at this site is less than 5,000 square metres. A total of 1200 clumps or mats have been counted, and monitoring since 1980 has not detected any change in this population.
The discovery of Diapensia took place in July 1951; C. F. Tebbutt, a birdwatcher, found the plant, recognising it as 'something different' (Grant Roger 1952). Diapensia was one of a trio of arctic plants discovered in Scotland in the early 1950s. Although no new species to Britain had been discovered in Scotland since Victorian times, in 1950, the arctic plant Iceland-purslane had been found on the Isle of Skye, and in 1952, Norwegian Mugwort was found on Cul Mor (Marren 1999). A photograph of the plant by Robert Moyes Adam taken on 14 June 1952 (soon after the initial discovery) is held by the St Andrews University Library [1].
It flowers at this site in May or June, the exact time varying from year to year. Some sources (e.g. Garrard and Streeter 1983 and the Glenfinnan Hotel website [2]) state that the species is found at a second site, but recent sources (e.g. Wiggington 1999, Preston, Pearman and Dines 2002) state that this is not the case.
The plant is listed in the 3rd edition of the British Vascular Plant Red Data Book (Wigginton 1999) as vulnerable. It is also protected under Schedule 8 of the Wildlife and Countryside Act 1981.
[edit] References
- Day, R. T. and P. J. Scott (1985) The biology of Diapensia lapponica in Newfoundland. The Canadian Field Naturalist 98: 425-439
- Garrard, Ian and David Streeter (1983) The Wild flowers of the British Isles. Midsummer Books, London
- Grant Roger, J. (1952) Diapensia lapponica in Scotland. Transactions of the Botanical Society of Scotland 36: 34-37
- Marren, Peter (1999) Britain's Rare Flowers. Academic Press, London
- Preston, C. D., D. A. Pearman & T. D. Dines (2002) The New Atlas of the British and Irish Flora. OUP, Oxford
- Tiffany, W. N. (1972) Snow cover and the Diapensia lapponica habitat in the White Mountains, New Hampshire. Rhodora 74: 358-377
- Wigginton, M. J. (1999) British Red Data Books 1. Vascular Plants (3rd edition). JNCC, Peterborough
