PlantFiles: Hollyhock
Alcea rosea var. nigra 'The Watchman'

From your friends at Botanical Interests, inc.: These seductive towers of edible black satin blossoms are a wicked addition to the back of the flower border, along a fence, or as an accent in the cottage garden. From a distance, the dark color of 'The Watchman' is as black as the moonless night sky, but on closer inspection you can see its rich purplish burgundy cast. Bees and butterflies will be lured to the 3"-4" flowers that exude ample pollen. Try growing them as a backdrop for pink, red, yellow, or white flowers or anywhere with full sun where you can use something tall and exquisite.(Hardy to zone 2, but technically a biennial. Hollyhocks bloom in the second year after planting. However, they do reliably reseed themselves, making them seem more like a perennial.)

The particular "black" hollyhock that I grow is this one- 'Watchman'. There are several 'black' cultivars out there. In my humble, non-expert opinion there isn't much difference in them at all. The only differences I have noted are the fact that there are "black" single flowered varieties and also there are double flowered ones. Irregardless of what name they go by I love them!

From the Seed Saver's Exchange: "Grown by Thomas Jefferson at Monticello, but mentioned even earlier by John Parkinson in 1629. He described this single hollyhock as being "of a darke red like blackwood." Appears black on overcast days, but will have a hint of red in the bright sun. Plant next to a white fence for a spectacular contrast. Self-seeding biennial, 5-6' tall."