When nettles don’t sting

Spotting the botanical look-alikes at Thorpe Marshes: a walker's guide to the plants that masquerade as nettles.

We all learn, sometimes by experience, that stinging nettles are best avoided. Stinging nettles have some wildlife value, not least as a larval food for the caterpillars of peacock and small tortoiseshell butterflies, and sometimes comma caterpillars too, but in general we avoid a close encounter.

Most of us also learn that if a ‘nettle’ has a flower, then it’s a dead-nettle and it doesn’t sting. I say ‘most’, though from my experience of guided walks at NWT’s Thorpe Marshes, not everyone has learnt this important life lesson.

New growth by a riverside path of mixed stinging nettles and dead-nettles, encouraged by the recent rain after the summer’s drought, reminded me how similar the leaves of these two species can look. That was before the helpful appearance of the white flowers of dead-nettles or the greenish-white, tassel-like strings of a stinging nettle.

White dead-nettle

It seems less well-known that dead-nettles and nettles are unrelated, taxonomically speaking. Dead-nettles are in the mint family, or labiates (Lamiaceae), while stinging nettles are in Urticaceae. "Labiates" is a fancy name for lipped flowers, featuring a ‘lip’ on the lower part of the bloom that is rather similar in shape to some orchids. This structure is easiest to see on large white dead-nettle flowers, rather than the smaller red dead-nettle.

All labiates, and this includes woundworts and several garden herbs such as thyme and sage, have square stems. On a guided walk I encourage people to feel this squareness, and that can take courage for a plant that looks somewhat like a stinging nettle. While stinging nettles also have angled stems, a specimen with a distinctly square stem and a lipped flower is sure to be a harmless dead-nettle.

Lesser known, also growing at Thorpe Marshes, is a plant called the stingless nettle. This species, also known as the fen nettle, wasn’t on my radar for many years: it’s absent from the field guide that was my ID bible for decades, the usually thorough Collins guide by Fitter, Fitter and Blamey.

Stingless or fen nettle.

Actually, "almost-stingless nettle" would be a more accurate name, though it’s pretty safe to handle — if you can be sure of its identification. The leaves are narrower than on a stinging nettle, it doesn’t flower until July and somehow looks less fierce. The fen nettle name is a useful hint: it always grows by water.

Stingless or fen nettle again - OK to touch!

There is another flower that masquerades as a nettle at Thorpe Marshes. This is gipsywort, and it’s also a labiate, though the tiny white flowers in a whorl around the stem are much less obvious than on a dead-nettle.

Gipsywort

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Chris Durdin lives in Thorpe St Andrew. He runs Honeyguide Wildlife Holidays www.honeyguide.co.uk and is the guide for the monthly guided walks at NWT Thorpe Marshes. This blog was first written as an article for Just Thorpe St Andrew.