Lax Midrib

Large vein that runs longitudinally in center of leaf appears flattened and broader than normal. Midrib is flexible so leaf appears to droop (Neuffer, Coe, and Wessler, 1997).

Four lower leaves show one leaf drooping significantly because of the flat vein; the other three leaves are slightly more upright because they're propped up together.
Lower surface of limp leaves.