Linked from
The 9 pages that link to Kale, each with the reason it gives.
Brassica oleraceaBroader topic: It represents the species' leafy, non-heading crop forms.
BroccoliRelated: Kale demonstrates the species’ contrasting leaf-focused form.
CauliflowerCompared with: Kale is harvested for leaves, not undeveloped flower structures.
Collard greensRelated: Kale is a close leafy relative often compared with collards.