Some similarities to : Stinging Nettle (Urtica dioica ssp. dioica) and to Small Nettle (Urtica urens) (see respective entries for differences), but Fen Nettle is much less frequently found, although it is thought it might be found anywhere in the UK.

It prefers damp places such as riverbanks and especially fens, particularly those around Wickham, Cambridgeshire and also in damp places or riverbanks, but unlike Stinging Nettle cares not for weedy places.

Un-like both Stinging Nettle and Small Nettle it is mostly without stinging hairs, but is covered in a dense mat of smaller and finer non-stinging hairs.

The only true way of differentiating between the two sub-species, Stinging Nettle and Fen Nettle, however, is by a chromosome count using a microscope and other instrumentation: Stinging Nettle is a tetraploid, with 2n-48 to 52, whereas Fen Nettle is a diploid with 2n=26. But usually, as a rough guide, Stinging Nettle flowers mostly between the 7th and 14th node up from the base of the plant whereas with Fen Nettle the flowers are usually to be found between the 13th and 22nd nodes from the bottom.