Dandelions are angiosperms, and even though I have yet to explain the amazingly elegant and complex mechanics of angiosperm reproduction, at a chromosomal level it (usually) works a lot like mammalian, or even human, reproduction: Every offspring has 2 parents. One parent- the male- provides a sperm. The other- the female- provides and houses an egg, or specifically an ovule. The sperm and the ovule both have ½ the number of the organisms standard, or fully diploid, number of chromosomes, and are said to be haploid.
Humans have 46 chromosomes, so each of our haploid sex cells has 23 chromosomes. Dandelions have 16 chromosomes, so each of their haploid sex cells has 8 chromosomes. Dandelion flowers are visited by bumblebees collecting nectar who inadvertently spread pollen from flower to flower, thereby pollinating various dandelions. And that’s how dandelions reproduce.
Only most of the time, it’s not. The vast majority of dandelions, including probably every dandelion you have ever seen (assuming you live in the continental US) is a chromosomal triploid that was created asexually from a parthenogenetic parent.
Side note: “triploid” is the specific instance of polyploidy- which we talked about when we looked at Sagebrush in the Newfoundland Mountains- in which the cell contains 3 sets of chromosomes, like a banana. (Only bananas can’t reproduce parthenogenetically.) So a triploid dandelion has 24 chromosomes.
That’s right, virtually all of the dandelions in your yard and your office park have not 16 but 24 chromosomes, and their ovules don’t need or accept pollen from other dandelions. Instead, they reproduce via a process called apomixis (or technically agamospermy in angiosperms) whereby ovules are created without meiosis, are therefore fully triploid right from the get-go, and set to develop into seeds without fertilization.
But some dandelions are sexual diploids and reproduce according to the standard angiosperm model. But to see this, we should leave
T. officianale in Central and
And now it gets even weirder. Some portion of the asexual triploids still produce viable pollen. Their sperm cells are diploid, and when they fertilize sexual diploid dandelions, they combine with the haploid ovule to create new asexual, parthenogenetic triploid lines. So new triploid lines are continually being created. Some of these lines exhibit high fitness and expand their ranges either locally, or when their seeds are introduced to a new locale, such as
T. officianale is therefore a species that has effectively hedged its bets when it comes to sex. When it has a good genetic model it runs with it asexually, but it still dabbles in sex to try out new lines from time to time, as a hedge against any possible threat (disease, parasite, predator) to which a given specific line might be vulnerable. It’s a reproductive schema far more sophisticated and nuanced than any of the other plants we’ve yet looked at, or our own for that matter.
Still another side note: The other day, when I was driving across town, past the House of 1000 Dandelions and such, I was struck by how much is blooming down in Yet another side note: The globe willows are now at their spectacular lime-green color peak in the valley. Here’s the group I photographed 3 weeks ago at the apartment complex by my office.
Yet another side note: The globe willows are now at their spectacular lime-green color peak in the valley. Here’s the group I photographed 3 weeks ago at the apartment complex by my office.
Next up: So what’s going on with the dandelions back here in