Another look at bog myrtle
After completing the drone photography on 18th October (Little Assynt in Autumn – 1) we made our way back along the All Abilities Path to the carpark (photo 1). We were once again struck by the appearance of the bog myrtle bushes flanking the Path, the subject of an article posted earlier in the year. We had finally located some female plants in fruit on a visit to Airigh na Beinne on Quinag on 28th August (photo 2), but these looked different (photo 3).
Since the rest of the party were ahead of us, we collected samples for closer examination later on. The fruits were more mature than those found earlier, but some of the catkins were rather odd. Female flowers, which had produced fruits, were clustered together at the tip, but nearer the base were the remains of male flowers, with obvious spent stamens (photo 4). We had thought that male and female flowers were normally borne on separate plants (the arrangement known as dioecious), but this was obviously too simplistic.
The Flora of the British Isles by Clapham, Tutin and Warburg (2nd edition, 1962) is beloved of an older generation of botanists, partly because it contains notes on the biology of the species described. The entry for Bog Myrtle or Sweet Gale Myrica gale, on p.568, reads ‘Fls mostly dioecious but plants may change sex from year to year and monoecious and hermaphrodite plants also occur’.
Monoecious individuals presumably have separate male and female catkins on the same plant, and hermaphrodite ones flowers of both sexes in at least some catkins, as in this case. Which poses the intriguing question – why and how do particular plants change sex?
A later visit
We were back walking the All Abilities Path on the sunny afternoon of 7th November, after a period of quite heavy rain. This had stimulated the production of fungal fruiting bodies across Assynt.
A large old downy birch, beside the wooded path leading up from Loch h-Innse Fraoich to the Viewpoint, had a conspicuous clump of reddish-brown gill fungi protruding from its gnarled trunk (photo 5). We later keyed these out as the wood-rotting species velvet shank Flammulina velutipes, a reminder that relationships between fungi and trees morph from mutual benefits in mycorrhizae to less friendly ones as the trees age.
Star jelly
On our way down from the Viewpoint, we began to notice small dark patches in the fine sandy gravel at the edge of the Path. They were most conspicuous in seating areas beside the Path (photo 6), and on closer inspection resolved themselves into pleated gelatinous masses of the cyanobacterium Nostoc (photo 7).
These somewhat mysterious objects have acquired an assortment of popular names, including star jelly and trolls’ or witches’ butter. They are probably the species N. commune, one of few terrestrial members of a mainly aquatic genus. Nostoc is also the photosynthetic partner in some lichens, such as jelly lichens and lungworts, characteristic of our local Atlantic Rainforest. In other parts of the world it is eaten or used as a traditional medicine.
Cyanobacteria are quite a large group, with some 2,700 species named and probably many more yet to be described. Some cause problematic ‘blooms’ in freshwater and marine habitats. Others form the structures called stromatolites found in lagoons on the west coast of Australia, fossils of which occur in the ancient Torridonian rocks that outcrop near the Split Rock at Clachtoll.
Although now relatively insignificant, they were for over a billion years the dominant photosynthetic organisms on the Earth’s surface, generating the oxygen that changed the nature of the biosphere.
Formerly known as ‘blue-green algae’, they are now recognized as Bacteria, one of the three highest groupings or domains into which all living organisms are divided. Animals, plants, and fungi, much more familiar to us, are a small part of the huge diversity of life forms in a second domain known as the Eucarya. The third domain in the Phylogenetic Tree of Life (photo 8) is the Archaea, specialized microorganisms that live in extreme habitats such as hot springs and deep-sea ‘smokers’.
Ian M. Evans and Gwen Richards