5th October 2009 – Rosebay Willowhearb.
During the summer months the very tall flowering stems of rosebay willowherb were conspicuous especially where they occurred in large beds on the sides of roads. A few of the loose tapering spikes of large bright pinkish purple flowers are still persistent but they are being replaced by the white, plumed seeds that flow over the countryside at the slightest breeze. The densely clustered flowers are always held horizontally and can be up to 48 inches high. The leaves on the upright and usually unbranched stems are arranged in spirals with each leaf being narrow at both ends, like those of a willow. They are hairless and have slightly toothed edges. The success of this willowherb is because it spreads in two very different but highly successful ways. The downy billows of seed are carried to new areas and then once established at a new site the plant can spread by the thick, woody roots which spread horizontally. These roots send up new shoots at intervals and large dense clumps are formed. The clumps can be so dense that they exclude most other types of plants although an exception is the foxglove and they can often be seen growing side by side.
Rosebay willowherb is now one of the most widespread of plants in the Highlands and is common in some parts of the Northern Isles but less common on the Western Isles. Its abundance tends to hide the fact that a hundred years ago it was rare as a wild plant although it was grown in a few gardens. In one of the old floras for the Highlands by G C Druce ‘The Flora of West Ross’ published in 1929 he describes the plant as being found at Gairloch, Loch Broom, Coigach and Applecross. He noted it as ‘certainly native on Knockan Rocks’ near Ullapool and that ‘In East Ross it ascends to nearly 2,000 feet’. The mystery is what turned this comparatively rare plant, one that is hardly likely to go un-noticed, into one that so readily colonises bare or disturbed places such as cleared woodland, roadside verges, railway embankments and even cracks in walls and chimneys.
The most marked change occurred in the two World Wars in the first by the extensive felling of woodland, including burning, as part of the war effort. In the second the bombing of areas gave disturbed and burnt areas that the willowherb relished and so much so this habit gave it its other common name of ‘fireweed’. This is not the complete answer as the spread in fact, particularly in the south, started before these two events. Perhaps it has been a combination of the wars and other factors such as new roads and the railway system all of which helped the remarkable spread. It could be that new areas to colonise is not the whole answer and the plant underwent a genetic change that made it a more vigorous and adaptive plant. It is easy to see why it could happen as the seeds of the plant are so small and light and each plant produces about 80,000 and all transportable by the wind. Over the years there have been theories that perhaps a new strain of rosebay willowherb came from abroad such as France or America, in the latter it is simply known as fireweed. Such theories have never been proven from the genetical examination of plants from various parts of the country. To see the splendour of this plant, its colourful flowers, and the vigour of the plumed seeds then simply drive or walk along the southern bypass around Inverness.