A rare aquatic specialist of temporary ponds. Now only found at two sites in the UK.
Adder’s-tongue Spearwort is a rare aquatic annual plant which is part of the buttercup family. It looks similar in appearance to the common Lesser Spearwort, but can be separated once plants are mature and in flower. The lower leaves of Adder’s-tongue Spearwort are more or less heart shaped in appearance, whilst the leaves of Lesser Spearwort are only ever lanceolate. The flowers of Adder’s-tongue Spearwort are small (5-9mm), whilst the flowers of Lesser Spearwort are large (7-25mm). Later in the season (August), once fruits have developed in place of the flowers, further confirmation is possible – Adder’s-tongue Spearwort fruits are tuberculate (covered in tiny lumps) whereas the fruits of Lesser Spearwort are smooth.
Adder’s Tongue Spearwort is a specialist of open wetland habitats, where it is dependent on poaching and seasonal inundation to supress competing plant growth and to create bare unshaded pond margins. It favours temporary ponds on grazed commons and roadside greens. It is a poor competitor and therefore requires extremely intensive grazing, or similar disturbance, to control emergent vegetation growth.
In areas where it is particularly abundant it has been found growing in more permanent grazed waterbodies. However in the UK it is only currently present in seasonal ponds.
Adder’s Tongue Spearwort is a classic mud plant, it germinates and starts to develop while water levels are still high, but typically doesn’t fruit until later in the summer once the water has dried out. Livestock poaching is very beneficial to seed germination by controlling competing plant growth and by turning over the soil, bringing seeds to the surface. Even a thin layer of leaves and silt could inhibit germination of seeds.
Distribution and threats
Adder’s Tongue Spearwort is listed as Vulnerable in the Red Data List of Great Britain and is protected by law as a section 41/42 Priority Species.
Although always a rare plant Adder’s Tongue Spearwort has now declined to just two sites in the Gloucestershire. The principle causes of this have been intensification of farming practices, infilling of ponds, artificial regulation of water levels, loss of grazing and nutrient enrichment. Adder’s Tongue Spearwort is intolerant of competition, without clean unpolluted water, intensive disturbance and control of competitors it is quickly lost from a site.