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Flowers and Fruits, part 6: 1-seeded Dry Fruits
A
fruit is a ripened ovary containing seeds.
There
are several different types of fruits. Many are crispy little
things that don't seem very fruity. Fruits can be loosely
categorized based upon whether they are dry or fleshy,
one-seeded or
several-many-seeded, whether or not they eventually split open and
release their seeds, etc. Also, some aggregate, multiple, and accessory
"fruits" are anomolous in
that they depart somewhat from the simple definition of "a
ripened ovary containing seeds."
First, let's examine one-seeded dry fruits that are indehiscent (don't
split open at
maturity). Most of these resemble, and are often casually referred to
as,
seeds.
Overview of the most
common one-seeded dry indehiscent fruits.
An
ACHENE is
a small, thin-walled one-seeded dry indehiscent fruit. It is a very
common fruit type, and the one most likely to be mistaken for a
(somewhat chunky) seed, given that it is nothing more that a
seed along with an additional thin covering, the "pericarp" (ovary
wall). It is the fruit type of our two biggest plant families --the
aster family (Asteraceae) and the sedge family (Cyperaceae), and is
found in many other families as well.
Below, a dandelion head in fruit. Dandelion is a member of the aster
family and, as such, has what appears to be a single blossom but is
actually a head-like cluster of many individually small flowers. Hence,
in fruit, the dandelion head is many small fruits. The individul fruits
are achenes. Or not. (See below).
MOUSEOVER the image
to see dandelion in flower.
Fruiting head of dandelion.
O.K. Maybe the
dandelion isn't the best example of an achene. Instead, it's a good
example of how picky-picky botanical terminology gets. That's because
according to this terrific book:
... we are informed of the existence of a "CLYPSELA" which is "an achene
that originates from an inferior ovary and has a hairy pappus." (The
pappus is the fluffy part of the dandelion fruit, consisting of highly modified sepals.)
Below, swamp buttercup, and a more technically correct example of an achene. Note that, here again, we see many small fruits
clustered together. This time however, the achenes are derived from the
separate carpels of a single flower (which therefore has an apocarpous
gynoecium).
MOUSEOVER
the image to see swamp buttercup in flower.
Swamp buttercup achenes.
Like
the clypsela, a few other, more widely recognized one-seeded
fruits
are best understood as being modified achenes. A NUT
is like an achene, but larger, and the pericarp (ovary wall) is thick and
bony.
Below, bur oak. Like the closely related chestnuts, acorns are
nutritious and were an important food source for native Americans. They
(red oak group acorns especially) contain bitter tannins that can be
leached out by boiling in water that is changed several times.
MOUSEOVER
the image to see bur-oak in flower.
Bur-oak acorns.
A GRAIN is like an achene, but the pericarp (ovary
wall) is papery-thin and tightly adherent to the seed. You cannot crack
open a corn kernel and remove a seed the way you can with a sunflower achene. The coat may be milled
off, as when white rice is manufactured by the processing of brown rice. The
grain is a fruit in one family only, but what a family! The grass family (Poaceae) is
very important because grasses are major components of
many ecosystems, and grass fruit forms the basis of practically all
agricultural economies, as rice, corn, barley, oats, wheat, and millet.
Below, foxtail-millet, a weedy
wild grass.
The grain is the
fruit of the grass family (Poaceae).
A SAMARA is an achene with a wing,
enabling dispersal by the wind. The whirlybirdy/helicoptery fruits of ash, elm, and maple are familiar examples os samaras.
Below, tree-of-heaven, an obnoxious Asian weed. It grows very fast. "The tree that grows in Brooklyn" is tree-of-heaven.
MOUSEOVER
the image to see a tree-of-heaven flower.
Tree-of-heaven fruits are twisted samaras with the seed in the center.
Another one-seeded
fruit that often gets mistaken for a seed is a peculiar one
found mainly in the parsely family (Apiaceae). Numerous
examples can be seen on the spice counter at the local grocery
store.
MOUSEOVER
the image for details of the cumin fruit.
The McCormick spice
company presents their excellent products in bottles
with beautifuly informative, botanico-anatomically correct labels.
Below, the woodland wildflower sweet-cicely. In the plant family
Apiaceae, the gynoecium is syncarpous with 2 carpels, each of which
contains a single ovule (seed). At maturity, each carpel continues to
enclose its seed, but the carpels separate from one another into
achene-like, one-seeded, "mericarps."
MOUSEOVER
the image to see sweet-cicely in flower.
The sweet-cicely fruit is a schizocarp that separates into one-seeded mericarps.
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