Dandelion (Taraxacum officinale)
Composite (Compositae) Family
Perennial

 

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.

239t.JPG (12963 bytes) 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.

205t.JPG (10659 bytes) 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.
495t.JPG (10803 bytes) 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.

218t.JPG (14318 bytes) 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.

29t.JPG (11191 bytes) 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.
30t.JPG (12221 bytes) 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.

500t.JPG (12172 bytes) 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.

505t.JPG (10967 bytes) 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.

507t.JPG (12935 bytes) 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.

508t.JPG (12813 bytes) 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).

510t.JPG (6873 bytes) 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.

219t.JPG (10598 bytes) 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.


©jdekker-1998

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