By Brian Ballinger
Many people with an interest in plants are attracted by the concept of rarity. Native plants are usually regarded as being rare if they are found in fewer than 100 10 x 10 km squares in the UK. The separate Red Data Book list is different and based on threat.
Scarce native plants are often thought of as dwelling on remote mountains or wild land. However, some are found in urban areas, including the following in Scotland.
1. Asplenium septentrionale (Forked Spleenwort)
This clump-forming fern differs from other Spleenworts by having forked linear leaves. It is often to be found in mountainous places, but it does occur in Holyrood Park in Edinburgh, some plants being near the road. It grows in crevices in vertical rock faces and occasionally on walls.
2. Crassula tillaea (Mossy Stonecrop).
This tiny member of the Crassulaceae family is often overlooked, but can often be spotted by its tendency to have areas of red colouration. It often grows on gravelly tracks and similar habitats where there is little competition.
It was formerly limited to parts of Southern England but it has been spreading and has recently been found in numerous places in Northeast Scotland, perhaps being spread by vehicles. It may shortly be deleted from the scarce list.
3 Dianthus deltoides (Maiden Pink)
This beautiful plant is a member of the Caryophyllaceae family and grows in grassland, heath and rocky places. It is a tufted perennial with pink flowers.
It is found in Holyrood Park in Edinburgh. I saw it on a grassy bank in Dundee some years ago but it did not persist. It is scattered in the British Isles and some sites have been lost.
4. Lychnis (Silene) viscaria (Sticky Catchfly)
This evergreen plant is a member of the Carophyllaceae and has recently been renamed Silene. Its name derives from the sticky glands on the stems and it has been cultivated in gardens.
It is mainly confined to cliffs in rocky places. It tolerates drought but not shading.
Most of its British sites are in Scotland and it grows on the cliffs of Holyrood Park in Edinburgh. It is widespread in the Northern Hemisphere.
5. Polygonum boreale (Northern Knotgrass). This annual plant is a member of the Polygonaceae.
It looks similar to the common Knotgrass (Polygonum aviculare), but it has bigger broader leaves, pink and white flowers and longer petioles.
It is common in Orkney and Shetland but rare elsewhere in Scotland, although easy to miss. There is a persistent population at Burntisland in Fife and I have seen it on a pavement in Dingwall.
6. Potentilla verna (tabernaemontani). (Spring Cinquefoil)
This early-flowering species is a member of the Rosaceae. A complication has been its repeated name changes – it was also called P. neumanniana recently.
It has 5 petals and long rooting branches. It grows in base-rich ground including coasts and crags.
In Scotland its urban sites appear to be all in Edinburgh (Holyrood Park and Blackford Hill). It is found in a few rural locations in Scotland, usually on calcareous soils. Globally it is restricted to Europe.
7. Sorbus rupicola (Rock Whitebeam)
This a shrub or small tree in the rose family and like other apomictic Sorbus species it produces seed without fertilisation.
It tends to grow on cliffs and rocky sites where access is difficult. It is found at high altitude and by the coast, but in small numbers.
It has been recorded in Holyrood Park Edinburgh and it is endemic to North West Europe.
8. Zostera noltei (Dwarf Eelgrass). This Zosteraceae family member is less common than Eelgrass (Zostera marina which now incorporates Z. angustifolia). The two eelgrass species often grow in close proximity. Zostera species are unusual in being submerged in the sea, only emerging at low tide.
Dwarf Eelgrass has narrow leaves and tiny flowers
Although scarce, some populations are large. It reaches the shore in a few urban sites such as Tain and Dingwall.
Reference: Stewart A., Pearman D.A., Preston C. D. (1994). Scarce Plants in Britain. JNCC