Identifying Red Dead Nettle is relatively easy at the moment, in the lower North Island anyway. Maybe in other places too. It's in full flower round here, and apparently also all round Palmerston North. It's much easier for an amateur like me to identify when it's flowering.
This is a Red Dead Nettle plant in our garden.
Red Dead Nettle (Lamium purpureum) isn't really a nettle. It's from the mint family. Its leaves have a very mild taste, especially the small, young leaves. You can eat them raw or cooked. I prefer them cooked - they're a bit hairy raw!
We had some in an omelet the other night. That was nice.
Red Dead Nettle is closely related to Henbit (Lamium amplexicaule), which also has edible leaves ... However, both plants can be confused with Staggergrass - which I'm pretty sure is NOT edible. (I haven't found any references to people eating it yet, anyway.)
Staggergrass has a hairier stalk than the other two, so that's one way to tell the difference and avoid it.
There are a couple of websites that I've found helpful in telling these three plants apart (and reassuring me that what I have in my garden IS Red Dead Nettle). Firstly there's the Massey Weed Database. And then there's the Virginia Tech Weed Identification Guide.
I wouldn't eat the flowers of either Red Dead Nettle or Henbit. I haven't read anywhere that they're edible - but I'm always more than happy to be corrected!