MIGLIA <MIGLIA%BITNET.IRMICMAT at vm.cnuce.cnr.it> wrote:
> Black leaves are not uncommon. Everybody knows the dark-red varieties
>of Prunus and Beechwood. The leaves of these plants look quite brown, e.g.
>very close to black and the trees do not show any impairement.
These plants are the result of selection for ornamental use aren't they?
The 'copper' beech has anthocyanin in its leaves (which is not uncommon as
a response to various stress-induced damage in many plants). The 'advantage'
to the tree in this case would appear to be the aesthetic qualities of its
leaves, rather than their photosynthetic potential but, I agree, that they
appear to grow normally.
>In these cases however it seems that leaves are rejecting not just green but
>also red,and the mix of green + red is brown. So the trees shouldn't have
>a problem of overheating.
>There is not clear reason why plants are green and not black, or brown. But
>probably the reason is in the phylogenesis. Terrestrial plants originated
>from chlorophyta, e.g. from green algae and still are green as those weeds
>What do you think ?
I think it is often the case that 'vestigial' traits persist because they
are not a selective _disadvantage_ and, indeed, they may confer an advantage
to a species by providing a gene pool from which adaptations can be made in
response to rapid changes in the environment.
This may be very important if the 'chaos' predictions of climate change
are correct: see Rind, D. Drying out the tropics (1995) New Scientist, 146
(1976), 36-40. We may *want* trees with black leaves to reduce the radiation
load on crops struggling to survive in the severe droughts anticipated.
Dr. A.J.Travis, | mailto:ajt at rri.sari.ac.uk
Rowett Research Institute, | http://www.rri.sari.ac.uk
Greenburn Road, Bucksburn, | phone:+44 (0)1224 712751
Aberdeen AB2 9SB, Scotland, UK. | fax:+44 (0)1224 716687