The consumption of energy in plants is important so one would suppose it is functiona.
Exactly, Peter,
Any such structure, (with decreasing benefit to survival), gets minimal resources and shrinks to get the plant a competitive advantage over other variants.
So now, as an extraordinarily thin wisp of a leaf in your photograph, is it “highly selected” and advantageous? Or perhaps now a vestigial non-functional remnant. How can we know? Study of variants versus the pollinators and ecosystem might have already been done?