Been really hot here the last few days and I'm noticing which established perennials are wilting. Purple leaved forms of Artemisia lactiflora and Lysimachia ciliata seem particularly bad and it got me wondering as to whether unnatuaral leaf pigmentations might somehow affect drought resistance. Has anyone noticed this in any other species?
I've never read anywhere that they have worse drought tolerance so I have no idea if this is the case or not, but since dark colors absorb heat, I would think it's possible that dark foliaged plants would transpire at a higher rate on a hot day than something with lighter colored leaves, and that would make them use up water at a faster rate. Many Mediterranean plants that are very drought & heat tolerant have silvery leaves, often with fuzzy textures, both of those contribute to helping them reflect sunlight instead of absorbing it, so it would make sense that having dark colored leaves could have an opposite effect.
Thanks for that, its a good point. I also wasn't sure whether having more purple pigment, might mean less chlorophyll and less efficient photosynthesis and less chance of closing stomata when under stress but its all a bit complicated. Your idea is more plausible. Its interesting to know if anyone else has noticed this, if indeed it really does make a difference. A guess a good way to test it is with purple leaved forms of waterlicsious things like lettuce.