That exact hypothesis has been mentioned before with regard to Alstroemeria leaf resupination: "...resupination may be an adaptation to the versatility of Bomarea vines to climb upwards, downwards, and grow horizontally, always orienting the ab.-top surface of the leaf toward light, even if this leads to untwisting or double twisting (Hill, 1939)." http://ncbi.nlm.nih.gov/pmc/articles/… The above work cites this paper from 1939 for that hypothesis: Hill A. W. (1939). Resupination studies of flowers and leaves. Ann. Bot. 3, 871–887. The discussion in the first paper on the interaction between resupination and phyllotaxis with regard to Alstroemeria leaf symmetry is an interesting read. Nathan At 11:33 PM 1/31/2013, you wrote: >Alstroemeria and Bomarea are relatives, they share a common ancestor. >Bomarea stems climb on other plants and if you look closely they actually >twist their leaves so that the leaves face the sun (I went out to look at >my plant just now and it did exactly that!). As a result, some of the >leaves will be resupinate (twisted), others will be non-resupinate >(regular). This may be the case with Alstroemeria too, but they don't climb >and the chances of them falling over isn't too great. But if that did >happen, maybe they too can untwist their leaves (experiment with your >plants and see). So perhaps somewhere in the common ancestor of Bomarea and >Alstroemeria, the leaves acquire this twisting mechanism and Bomarea kept >it, some Alstroemeria kept it, and others lost it as Jane pointed out. It >makes sense. If you don't use it, you loose it. > >Nhu