Evolution of Lysichitum

From: mossytrail at hctc.com (mossytrail) on 2008.03.14 at 02:02:07(17178) I was in the wetlands today. Lysichitum americanum was abundantly in bloom. I found one group with all-green spathes. Now that is probably not so unusual in itself -- a spathe, after all, is not so very removed from a leaf. But still, most examples do have the clear, bright yellow spathe. These green-spathed ones appeared at first glance not to be in bloom. It made me wonder: what is the relative importance of spathe color vs. plant odor in attracting pollinators? I am not even certain what the pollinators are in this case -- perhaps the delicate, long-legged gnats I saw in a few inflorescences? As we know, the other member of the genus, L. camtschatcense, has white spathes. Presumably, it, too, is quite capable of producing abnormal green-spathed forms. They would be a different shade of green -- a plain green infusing an otherwise-unpigmented spathe, as opposed to the green overlying yellow of L. americanus. This started me pondering. Presumably, either L. americanus was the evolutionary ancestor of L. camtschatcense, or their common ancestor also had a pigmented (probably yellow) spathe. This is simply because it is easier for a colored plant part to lose its pigment, than for a white plant part to evolve pigment. Most likely, L. americanus will produce an occasional "albino" or white-spathed individual; but the likelihood of L. camtschatcense producing a yellow-spathed individual would be far more remote. There is of course no way to know the spathe color of the fossils L. washingtonensis and L. nevadensis (and in any case, these are only tentatively identified as Araceae), but (assuming they are in fact of this genus) at least one is likely to have had a yellow spathe. As I continued pondering, I wondered where the genus originated, and where it differentiated into the extant species. If the aforementioned fossils are valid, they suggest a North American origin, which would be consistent with the spathe colors: L. americanum having the primitive character and being geographically nearer the point of origin, L. camtschatcense having the derived character and being in the geographically remote range. One possibility is that the white-spathed population had some ability to spread to Asia that the yellow-spathed plants lacked. On the other hand, it is possible the genus had reached Asia before differentiating, and that the Ice Age glaciations then isolated the Asian population and allowed it to speciate in situ. +More The question then becomes, if we suppose the white spathe was originally an abnormality in an otherwise yellow-spathed population, what caused it to become the normal condition in the one species but not the other? An interesting aside: inside the spathes, I found small true bugs which may have been Miridae. If so, this is a parallel to the Xanthosoma inflorescences I sudies in Monteverde, Costa Rica, which had their distinctive Miridae communities inside the spathes. What is it with Miridae and Araceae spathes? Jason Hernandez Naturalist-at-Large

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