THE OCCURRENCE OF A NUT OF TRAP A NATANS L. IN THE OUTER HEBRIDES, WITH SOME ACCOUNT OF THE PEAT BOGS ADJOINING THE LOCH IN WHICH THE DISCOVERY WAS MADE

Abstract

For a number of years, expeditions organized by the Department of Botany, King's College, Newcastle upon Tyne, have been investigating the flora and fauna of the Inner and Outer Hebrides. During the course of this work, a number of plants new to, or rare in, the British Isles have been detected. Amongst these were American forms like Naias fiexilis Rostk. and Spiranthes stricta Nelson, Arctic-Alpine species such as Carex capitata L., C. bicolor All., C. glacialis Mack., Erigeron unifiorus L. and others, like Illecebruin verticillatum L., Juncus capitatus Weig, and Cicendia pusilla Griseb., only previously recorded from far-distant stations. To the latter may now be added Trapa nzatans L., although the material collected is not of recent origin. A single nut was found entangled in a dense mass of Potamogeton pectinatus L. debris washed up on the south-east shore of Loch Ceann a' Bhaigh, on South Uist, in the summer of I944. A careful examination of the fruit soon revealed the fact that it was not a living specimen, but that it must have been washed out of peat deposits somewhere in the vicinity of the intricate system of lochs and lochans of which Loch Ceann a' Bhaigh forms the lowest member. The nut was in perfect condition, and agreed in type with the var. coronata Nath. as described and figured by Schroeter (I899). However, it was more slender and possessed more acuminate spines than the example figured. It resembled, rather closely, one illustrated (fig. i88) by Gunnar Andersson (I898) from a peat bed in Finland. Trapa natans has not been known to occur in Britain since the Ice Age, although it has been listed from the Cromer Forest Bed by Reid (I899). Still, the present discovery, although important, is not very astonishing, as remains of the plant have been reported in post-glacial peats in Norway, Denmark, etc. (Gams, I926), in areas beyond the present European range of plant. From the facts outlined above it will be clear that the exact source whence the nut was derived is unknown, but, very fortunately, careful scraping of its surface yielded enough peat to provide a count of I40 tree-pollen grains. Furthermore, during the I939 expedition, several peat cuttings had been examined in the general neighbourhood, and samples taken for pollen determinations. Material was therefore available for attempts to discover the source and relative age of the specimen. Three of these peats have been examined, and two are reported on in detail. The first, about 2 m. in depth, was collected on the shores of Calvay Island, lying at the