#ranunculaceae

I thought this was the European Water-crowfoot, Ranunculus trichophyllus, but according to naturalist89577 on iNaturalist the aquatic buttercup in New Zealand is anatomically distinct.

The New Zealandish Batrachium is not identical with northern hemisphere R. trichophyllus (the pedicels are longer, the achenes have a persistent style). The whitish stem and the slightly winged achene might indicate relationship with R. baudotii.

Ranunculus means 'little frog' and may refer to the number of species of buttercup that grow near water - admittedly not all of them to the degree of Batrachium, which just means 'frog'. Water-crowfoots may have two different kinds of leaf - thread-like leaves underwater and broader leaves floating at the surface. In some species a third, intermediate leaf type can be found.

Crowflowers are mentioned in Hamlet - see this article for an investigation into what flowers Sir John Everett Millais’ included in his famous 1852 painting of Ophelia.

The genus probably evolved in Northern Eurasia in the late Eocene or Oligocene, and rapidly spread worldwide. They were even growing in Antarctica until the second half of the Pliocene, as the continent was starting to freeze up.

Old man's beard

f. Ranunculaceae