I don't really recognise it, its not what i thought when I read the title.

did they sting like a nettle first? The leaf does have a nettle type shape. There are several plants [non-nettle] that have sap that can do this. Keep your skin out of the direct sunlight as this can often make the rash worse.

Were any of them in flower? can you add a photo of the plant in the ground?

sorry I am not much help.

i thought it might be wilting nettles. Perhaps we could have a better picture of the leaves?