Freshwater pearl mussels spend their adult lives anchored to the river bed, filtering water through their gills and improving the quality of the water for other species.

The Sitka spruce was introduced into the UK from North America in the 19th century. It has been widely planted as a forestry tree; look for classic needle-like leaves and pale brown, domed cones…

Introduced from Japan in the 19th century, Japanese knotweed is now an invasive non-native plant of many riverbanks, waste grounds and roadside verges, where it prevents native species from…

Toadflax-leaved St John's-wort has star-shaped, bright yellow flowers. It is a rare plant, with most of its population existing on Dartmoor. It likes steep, sunny slopes, acidic soils and…

These non-native limpets arrived from America in the 19th century and are now widespread in the UK. They form stacks and have a specially adapted shell which, when flipped upside down, looks like…