Black Iris is a two-block high flower. It is a more common variant of the Yellow Iris, which is found exclusively in the Gladden Fields.
Black irisses are fairly common 'double flowers' in
Wilderland, Dorwinion and Rhûn Forest, where they grow in most sub-biomes.
Like any flower, these can be grown with a random chance of appearance by using
bonemeal on the soil of the biomes in which they naturally occur. Like other double-high flowers, it's also possible to use bonemeal on the plant itself.
This flower can be used in a regular crafting table or the player's inventory to create
dye, alike to other mod flowers. Unlike the name implies, it doesn't yield black, but two pieces of purple dye.
Wilderland (standard biome variant)
Dorwinion (standard biome variant)
Rhûn Forest (standard biome variant)