These two species of plant have similar-looking flowers but are most easily told apart by their different leaves. The common name Blue Larkspur usually refers to Delphinium parryi which has narrow palm-like leaves, while Spreading Larkspur is Delphinium patens and has broader 3-parted leaves. The flower stalks of Delphinium parryi are shorter (less than 1 1/2 inches) relative to Delphinium patens. Blooming occurs in June and July for the slender-leaved Delphinium parryi but earlier - March to May, or sometimes through summer into fall - for Delphinium patens.
The flowers of both species are a striking blue-purple and have the characteristic shape suggested by their common name. The spur of the flower is actually one of its 5 sepals. There are 4 petals, 2 white and the other 2 white or blue-purple. Leaves appear at the base of the plant.
These plants have narcotic properties (known for cattle poisoning) and were also used as a tincture to treat lice, scabies etc.
The species name Delphinium is Greek for dolphin, referring to the larkspur shape. The species name parryi is for Dr. Charles Christopher Parry, a 19th century botanist, and patens means spreading.