Larkspur, Delphinium and the closely allied annual delphiniums, is a tall spike-flowered plant of the buttercup family, its blossoms most often a brilliant blue. Two names describe the flower's shape: larkspur, for the long backward spur of each bloom, likened to the hind claw of a lark; and delphinium, from the Greek for dolphin, for the resemblance of the unopened bud to a dolphin's body. It is a plant to admire and not to eat: larkspur is genuinely poisonous in all its parts, a serious hazard to grazing livestock, a fact stated here plainly as caution.
Despite its toxicity, or rather because of it, larkspur had a genuine practical use: a tincture made from the seed, rich in the alkaloid delphinine, was a standard folk and even early pharmaceutical treatment for head lice and body lice into the twentieth century, applied externally to the scalp and clothing rather than taken internally, a documented use of the plant's poison turned to a specific practical purpose. The same alkaloids that made it dangerous to livestock are still studied today for their action on the nervous system, though none of this makes any part of the plant safe to handle carelessly, since the alkaloid is absorbed readily even through the skin.