Help: humongous leaves!

MEK104 at psuvm.psu.edu MEK104 at psuvm.psu.edu
Tue Oct 27 13:57:20 EST 1992


>A twelve-year-old kid in our neighborhood (southern Maryland, USA) recently
>found an oak leaf (Quercus velutina, I think) about four times larger than
>any I've previously seen -- it's about 35 cm long by 30 cm broad.  He and
>some neighbors are very excited about this find and have called the local
>newspaper (it's a small town) and asked the local botanist - me - for some
>sort of explanation.  I haven't the slightest clue.

>Can anyone offer a plausible suggestion of some things that might cause one
>enormous leaf on an otherwise normal tree?  Somatic mutation?  Some odd sort
>of double development (maybe two buds fused or something)?  I'm 90% sure the
>blasted newspaper is going to call me for an "expert opinion," and they're
>not going to take any disclaimer like I'm only a recently displaced
>Californian physiological ecologist and so how should I know.  So any help
>would be VERY welocome!!

Black oak (Q. velutina) is notorious for dramatic differences in sun versus
shade leaves.  Sun leaves have much deeper sinuses and shade leaves often
have no sinuses at all, only the small bristles at the end of secondary
veins (where the lobes should be).  I've seen rediculously large black oak
leaves in forest understories in Pennsylvania many times.  While I agree
that 35 cm is probably the largest I've heard of, its probably just an
extreme case of the polymorphic nature of black oak (25-30 cm lenghts are
not uncommon).  In fact, we teach our dendrology students here to look for
the polymorphism in sun versus shade leaves as one way to help ID black oak
from northern red, scarlet, and pin oak.

Other morphological traits typical of shade leaves are: lower specific leaf
mass and leaf density, thinness, fewer stomata per unit leaf area and larger
guardcells.

Mark Kubiske
School of Forest Resources
Penn State University


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