Well, it looks remarkably like Iris pseudacorus. There's a cultivar called Roy-Davidson which has those more pronounced brown markings. But usually it's a marginal pond plant.

Thanks floral

'Ray Davidson' and 'Berlin Tiger' are both cultivars of I. pseuodacorus, but I eliminated them as I.p is an aquatic/bog plant. These are growing in an herbaceous border. The plant behind it is a Hydrangea.

Afaik I pseudacorus can be grown in a normal bed as long as it gets sufficient moisture.

Eyebright...Dwarf Bearded Iris?

Link..Click to see.

It looks too tall and slender for a dwarf. And the rippling on some of the leaves is very pseudacorus-like.

when I worked as a student at some botanical institute, those ripple were drummed into us as a sure sign for Iris ps., instead of Acorus calamus, it was a tiny institute and they even had a ditch with tose two species growing next to each other,

the markings make it a fancy or hybrid I pseudacorus, in water it is a total thug, in moist soil probably still formidable

PS: I looked it up on a very interesting perennial nursery in Germany, they describe its water demands from moist (like most regular garden perennials) till in shallow water, it is supposed to tolerate occasional flooding

the photograph showed a flower with tiny dark purple markings, so perhaps the one on this thread it is just a selection