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 7 many shapes DHJanzen100316.jpg high resolution
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| Leaves (and leaflets) come in many shapes, and many different selective pressures operate on them. While there are general correlations between certain leaf shapes (and sizes) and certain ecological circumstances (a correlation generated by both direct environmental responsiveness of the plant and by selection for certain leaf traits by certain environments), in many cases either the forces leading to given leaf shapes are invisble to us or lost in history (and the leaf shape is thus an anachronism). A specific example of leaf shape mystery is these leaf shapes, each from a different species of vine in the tropical genus Passiflora (the Passifloraceae, the passion fruit family). All were growing in the same place in Costa Rica, no two are the same yet since they are all of the same genus, presumably they all have the same ancestor. The only thing on can say for sure is that each species is accompanied in the habitat by one or more other species in other families with very similar leaves. It is tempting to call them mimics, but, if that is the case, mimics of what and what is the selection pressure for the resemblance. One possibility is that by looking like leaves of other species, the Passiflora gain protection from Passiflora-eating species of butterflies that cannot as easily locate the food plants on which to lay their eggs. | ||
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