For some reason, many amateur gardeners I encounter think Delphinium and larkspur are two different flowers. It's alway a little tricky with common names — that's why the pros use latin names — but larkspur is the common name for the Delphinium genus.
This patch (Delphinium grandiflorum?) is the progeny of seed brought originally from Wisconsin to Riverside Park nearly 20 years ago. They bloomed prolifically for a few years, then disappeared for a while, then came back with staying power, springing up each year here and there, or where some gardener sows collected seeds. These were collected last fall by volunteer gardener Melanie Bean and sown around the perimeter of her garden.
While we seemed to have only blue flowers in the early years, there are now white and pink too — due to recessive genes in an isolated breeding population?
Larkspur along the Hudson RIver Greenway at about 97th Street.