MadSci Network: Botany

Re: Sweet Gum Tree Fruit - Why Bother ?

Date: Thu Mar 10 12:00:24 2005
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1110330299.Bt

Sweet gum (Liquidambar  styraciflua) seeds have wings, as you indicated, so are
mainly dispersed by wind. Ninety-six percent of the seeds usually fall within 61
meters of the tree with the record for dispersal at 183 meters.

The sweetgum fruit is a multiple fruit consisting of many capsules. A possible
"advantage" of that is that many seeds are produced in one structure. Multiple
fruits are produced when fruits produced by many separate flowers grow together.
Multiple fruits also occur in pineapple, mulberry, figs and Osage orange. 

The sweet gum fruits stay on the tree most of the winter so they may act
primarily as "launching platforms" for the seeds. It is perhaps analagous to the
cone of some pine trees, which also have winged seeds dispersed mainly by wind.

I agree that it seems unlikely that the sweetgum fruit is adapted for clinging
to fur. Who advocates that theory? There are some (Barlow and Martin 2002,
Barlow 2001) who believe that several native American trees have adaptations to
large herbivorous mammals that are now extinct. However, I don't believe sweet
gum was one of their examples. They usually mention the fruit of honey locust,
Kentucky coffee tree and Osage orange.


Sweetgum (Liquidambar styraciflua)

U.S. Department of Agriculture, Forest Service. 1965. Silvics of forest trees of
the United States. H. A. Fowells, comp. U.S. Department of Agriculture,
Agriculture Handbook 271. Washington, DC.

Unusual Fruits Called Capsules

Multiple Fruits

Barlow, Connie and Paul Martin, 2002. The Ghosts of Evolution: Nonsensical
Fruit, Missing Partners, and Other Ecological Anachronisms. Basic Books

Barlow, C. 2001. Ghost Stories From the Ice Age - methods of seed dispersal that
date back to Ice Age
Natural History. (Sept.) 

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