Dandelion Reprise
(This column was first published in the June 2,
2003 issue of The Buffalo News.)
That was news to
me. Like most of us, I had seen bees actively probing the bright yellow flowers
for pollen and nectar, I assumed pollinating them in the process as they moved
from flower to flower. As a youngster I had also often contributed to the
distribution of the seeds that formed in those spherical seedheads by blowing
them off into the welcoming breeze.
All that seemed
quite normal. It took some research to find that my understanding of these
weeds was not only limited but in some ways quite wrong.
First I learned
that each dandelion blossom is not a single flower with many petals but instead
is a collection of many flowers, each yellow ray one of them. By dissecting a
blossom I found well over a hundred of those rays. It is this feature that
assigns the dandelion to the composite family along with the daisies,
goldenrods and sunflowers. Unlike those other composites, however, the
dandelion's individual flowers are all alike.
Dandelion
blossoms close up at night. (Their appearance in this form is the source of one
of the weed's most descriptive common names: swine's snout.) I followed the
instructions in the Stokes' Guide to Enjoying Wildflowers and picked a
blossom shortly after it reopened early one morning and was able to see the
progression the individual flowers followed. In the middle of the blossom each
ray was still tightly closed into a tube. Farther out these tubes had already
opened to disclose delicate little Y-shaped stigmas. Looking at the blossom
from the side, I could see them waving gently above the rest of the blossom.
They are the female parts and the tubes the fused male parts of the individual
flowers.
That sequence
still seemed to me to fit the normal pollination sequence. Wouldn't a bee or
other pollinator inadvertently take pollen from one flower to another and
wouldn't the close proximity of these sexual parts make that all the easier?
It turns out
that this normal cross-pollination does not take place. Instead, like other
composites, the dandelion is apomict, that is, each of those tiny flowers
produces its seed without pollination.
Apomixis is like
cloning in that the offspring is usually genetically identical to the parent.
But it is that word "usually" that creates problems for botanists.
Every time a significant mutation occurs to change an individual flower's
genetic code and the seed of that flower germinates successfully, a new variety
or even species is produced.
My field guides
list several dandelions: common, red-seeded, fall and dwarf, the last two even
in different genuses from our common dandelion. But botanists identify hundreds
of additional mini-species: in England alone, for example, more than 150.
We can leave
those problems to the professionals, but there are other composite yellow
wildflowers with which dandelions are often confused. Like the common dandelion
most of these look-alikes are aliens. And they all have those many-rayed yellow
blossoms. The earliest blooming is coltsfoot. You need only look at its
asparagus-like stem to see that it is different. And its flowers disappear
early too.
The sow-thistles
differ in other ways. Unlike dandelions they usually have more than one blossom
on a stem that divides near the top and their leaves are prickly-edged. And the
yellow goat's beard has grass-like leaves. The cat's-ear has hairy leaves and
the lamb succory has stems that are swollen near the blossom.
These
ubiquitous wildflowers (a.k.a. weeds) may not be our favorites but they
add their lovely yellows to our summer fields.-- Gerry
Rising