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fruits and nuts

David W. Kramer kramer.8 at OSU.EDU
Sat Jun 27 12:31:10 EST 1998

You can add beechnuts (also in the Fagaceae) to your list and some authors
have also called the fruits of basswood (Tilia) nuts!

If your students are learning the various fruit types they might enjoy
using Steve Wolf's Fruit Key at his outstanding web site, CSUBIOWEB:


If you compare introductory botany textbooks, you find lots of confusion
and errors about fruits in general and nuts in particular.  Field manuals
often perpetuate the errors probably because the authors know they will be
used by many amateurs (and professionals!) who are unaware of the subtle
distinctions or do not want to bother with them!  Thus, most field manuals
use "nut" as it is used in the vernacular.

Some authorities (Esau, Eames, et al.) treated nuts as morphologically like
achenes (dry, indehiscent) except for being 1) larger, 2) syncarpous
(having two or more, fused carpels), 3) having an extremely hard, thick
outer wall, and 4) usually surrounded by a "cap" or "husk" derived from
bracts.  One response to your inquiry said walnut (and the closely related
butternut and hickory nut) is a nut but others consider it to be a drupe
(just as almonds also are the stones of drupes).  The debate hinges on
whether the fibrous outer husk of the walnut (and the others) is derived
from ovary tissue (making the "nut" a stone of a drupe) or bracts and
hypanthium (making it a true nut)!

Good luck finding "an authoritative source" for this information!  I've
spent most of an hour (thanks for the incentive!) looking through more than
a dozen "authorities" and I can find no agreement!  It's enough to drive
you nuts!

>Will someone please give me some examples of plants that bear fruit in the
>form of true nuts?  I know hazelnut and acorn are, and that most others
>called nuts are not, but I cannot find an authoritative source of this
>Peggy E. Pollak
>Department of Biological Sciences
>Northern Arizona University
>Flagstaff, AZ 86011-5640

Dr. David W. Kramer
Department of Plant Biology
Ohio State University at Mansfield
1680 University Drive
Mansfield, OH  44906-1547
(419) 755-4344  FAX:  (419) 755-4367
e-mail:  kramer.8 at osu.edu

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