The arrowhead leaves of Cuckoo Pint.
It's also a garden plant in my garden, popping up all over the unmown lawn and in the flower beds. Not so welcome there but quite difficult to eradicate as the roots go deep.
BTW I haven't heard a cuckoo in Thornbury for decades.
Photo: Chris Romeiks
In April come she will
In May she comes to stay
In June she changes her tune
In July she prepares to fly
In August go she must