A boat-shaped collective phyllome structure (PO:0025023) that consists of the two lowest petals (PO:0009032) of a papilionaceous corolla (PO:0009059).
Source:ISBN:9780023681905
Comment
The two petals of the keel are often fused at the apex and free at the base. The keel projects toward the front of the flower. Found in the flowers of some Fabaceae.