Dandelion Reprise


(This column was first published in the June 2, 2003 issue of The Buffalo News.)


When our state botanist, Richard Mitchell, spoke at the Niagara Frontier Botanical Society banquet two years ago, he mentioned that the dandelion is propagated by a very unusual process.


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