Stories from Staffa: Flower notes from a small isle

Sheep last grazed on Staffa in 1996, and since then a thick thatch of grass and other plants has developed. Despite the lack of grazing, the varying soil thicknesses, natural drainage, grazing by geese and the trampling of visitors’ feet continue to present a host of habitats and a wide floral diversity.

Staffa supports over 70 species of flowering plants as well as many mosses, ferns and liverworts. If you include the marine algae above and below the tide lines, this number would leap again.

Lichens and other fungi are usually left for botanists to describe, although in fact they differ from plants as much as insects, birds and other animals. Lichens are fungi which embody algal cells. The fungi provide a UV-protective, humid environment for the algae, which provide sugars and other foods to the fungi through photosynthesis.

The intimate relationship between fungi and algae is often cited as a special one in lichens. In fact, it’s unusual to find any organism which does not live intimately associated with microbes. All animals have gut bacteria essential for digestion, immune systems and general health, and virtually all plants have fungal and bacterial associations without which they would fail to thrive, or even die. Lichens, or ‘lichenised fungi’, are just one example among millions of such inter-specific relationships.

The lichen-covered rocks above are close to the high tide mark. There is in fact no rock visible in this image, as every square centimetre is covered by lichens!

The seemingly black Verrucaria maura grows extensively on rocks that are frequently washed or sprayed by salt water. Over it grows the orange Caloplaca thallincola and yellow Xanthoria parietina. The grey lichens may be Rhizocarpon, Ochrolechia or another species, all equally adapted to living in a salt- and mineral-rich environment.

The image of lichens simply co-existing belies their slow-paced struggle for space. A time-lapse sequence would show a scene of constant motion as individual lichen patches grow and shrink, battling with each other and the elements.

Lichens are believed to have been the first terrestrial organisms on land, preceding plants by a long time during the Precambrian era some 1,300 million years ago. Through photosynthesis, lichens would have helped to change Earth’s atmosphere from one rich in carbon dioxide to one rich in oxygen. Although this happened over many millions of years, in the scheme of Earth’s history this change was relatively rapid and is called the Great Oxygenation Event.

Bright orange lichen (Xanthoria parietina) grows on rocks close to the sea and in other environments rich in minerals. In fact, it’s one of the most pollution-tolerant lichens, often found in cities where the air is rich in sulphur compounds, metallic particulates and nitrogen oxides. The name Xanthoria comes from the Greek xanthos meaning yellow, and parietina means found on walls. Its colour gave rise to a belief in its use as a treatment for jaundice. While this is a fallacy, the lichen does seem to have interesting anti-viral properties such as in the treatment of human parainfluenza viruses. It’s also a source of a yellow dye – although the yellow pigment xanthorin is actually produced to absorb UV radiation and protect the underlying tissues.

Mostly of flowering plants, the photos below were taken between May and early August. They show just a small selection of those found on Staffa, with some notes about their names and other idiosyncrasies. The rich flora sustains an equally rich variety of insects, other invertebrates and terrestrial birds. I’ve included an image of the now nationally scarce common blue butterfly but some other creatures will be described in the next chapter of Stories from Staffa.