The common walnut tree produces a large, brown nut that is familiar to so many of us. It is an introduced species in the UK, and can be seen in towns, gardens and parks.

This small, white heron is an increasingly common sight in parts of the UK as it spreads north from continental Europe.

This slim fish is usually found on gravelly parts of the seabed, close to shore, but can turn up in rockpools.

The Marsh helleborine is a beautiful orchid of fens, wet grassland and dune slacks. Growing in profusion in places, look for reddish stems and white-and-pink flowers.

Red squirrels are native to the UK but are a lot rarer than their grey cousins. They live in a few special places across the UK thanks to reintroduction projects.

The delicate, tube-like, violet-blue flowers of Skullcap bloom from June to September in damp places, such as marshes, fens, riverbanks and pond margins.

The fine, downcurved bill of the treecreeper makes this tit-sized bird unmistakeable. Look out for it in woodlands and parks, literally 'creeping' around tree trunks.

Ground-elder was likely introduced into the UK by the Romans and has since become naturalised. A medium-sized umbellifer, it is an invasive weed of shady places, gardens and roadsides.

The Norway spruce was introduced into the UK from Scandinavia in the 16th century. It is familiar to us all as the 'original' Christmas tree and displays hanging, reddish-brown, oblong…