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Virtual WeedPatch
Weed ID
dlion.html
Composite (Compositae) Family
Dandelion (Taraxacum officinale)
Dandelion is one of the most common weeds many of us encounter. They
infest many different habitats, including probably your lawn at home. They
are common in waste areas and in pastures. Dandelion do not thrive as well
in fields that are tilled every year. This is due to the fact they thrive
best when allowed to develop into perennials with large perennating taproots.
Dandelions reproduce in two ways. The first is
by seed, shown in the picture (left). The dandelion seeds below were
snatched out of a pasture in southern Ontario, Canada. Notice the brown
seed with the long stalk ending in the tuft of hairs at the
end. The tuft of hairs and slender stalk allow it to float on the wind.
This wind-blown dispersal and spread mechanism is the reason some neighbors
get angry when the seed from one blows over into the yard of the other.
We all have different weed management expectations.
Early in the spring dandelion shoots
from seed emerge from the soil, as you can see in the two pictures (left;
below). These leaves of dandelion remind me of lettuce for some reason.
Maybe I shouldn't work during lunch.
Here is another picture of dandelion emerging from
the soil in the spring. If the dandelion plant was a perennial it would
probably have a basal rosette already on the ground from the previous year.
Sometimes, though, tillage in crop fields breaks up the rosette and the
taproot remains alive in the soil. This perennial taproot can act like a
seed in the soil and germinate in the spring. The dandelion plants emerging
below could have come from either a taproot fragment or a seed. Vegetative
plant parts that act like seeds in the soil comprise the "bud bank",
which is similar to the seed bank.
Here is a worm's eye (do they have eyes?)
view of the dandelion plant, as well as the rosette. This intimate
look at the bud bank reveals several interesting features of dandelion.
First notice the leaves on top. They form what is called a rosette,
a cluster of leaves arising from a central axis with no stalk or stem. In
this southern Ontario dandelion I have cut away some of the leaves. If you
look closely at the area where the leaves are cut away you can see a white
milky juice. Below that is the taproot. These taproots can be
harvested and roasted and made into a coffee substitute, like chicory. I
used to do that as a starving grad student many years ago. This plant has
also been used as a folk remedy diuretic. The French common name for dandelion
is "pissenlit", which translates in English as "piss-in-bed",
so apparently it worked for some folks.
Dandelion, like all organisms, has a few oddballs
in the population. Here are mutants of dandelion. Notice the weird
stalk and seedhead. Both seem to be made from many stalks and flowers welded
together into a fat, grotesque part. This condition is known as fasciation.
My then 2nd grade daughter discovered them in our
pasture and brought them to my attention, and we published a research article
together on them. These dandelion mutants could be due to a different genotype
(genetic polymorphism), or they could be due to abnormal developmental changes
(somatic polymorphism) within a normal plant. Both are important types of
biodiversity in weeds we will learn more.
A dandelion plant in flower can
be seen in the picture below. The leaves of the rosette surround
a flower stalk that has grown up and ended in a yellow flower.
In this picture from Ontario dandelion are competing with equisetum (aka
field horsetail), an ancient plant that likes poor drainage and reproduces
by rhizomes, tubers and spores.
The Michigan pasture (left) is choked
with flowering dandelion. Although growers become concerned with this number
of weeds in their fields, dandelion usually doesn't cause much yield loss
to fields, they seem to cooperate with their neighbors. This cooperation
is due to many factors, including that they conduct their life cycles at
different times than pasture species and thus both avoid competition.
Left is a single dandelion flower. Notice
the yellow ray flowers that have emerged from the seedhead. In the center
of the flower head you can see nascent flowers in green getting ready to
do their thing.
The beautiful yellow flowers don't last
too long in the field. Soon the yellow petals give way to seed development
and they dry out with maturity. It is then that we see the white globe-like
balls of seed on the heads as in the picture below. Yellow flowers and white
seedheads on different plants of a population overlap in their development
as you can also see (left).
This picture below shows a closer look
at the mature dandelion seed (right) on the head before it is dispersed
away to some neighbors lawn. On the left side of the picture is a seedhead
after the yellow petals have gone (still visible at the flowerhead base),
but before it has opened. The white at the end of the seedhead (left) are
the tufts that carry the seed with the wind. On the right is the seedhead
as it next appears. The green enclosing flowerhead opens and the seeds form
their characteristic white globe of seed. The first puff of wind and the
seeds come loose and float into some nearby lawn.
Left is a closer look at this mature seedhead.
You can see the brown seeds attached to the flowerhead base, and the slender
stalk ending in the white tuft that catches the wind.
