The willows on the creek banks are big. I’d like to say they’re ancient, but I don’t know that. My parents planted a willow at the home place in West Texas when my younger brother was born. The last time I saw it, almost 60 years later, it was still smaller than these trees along the creek. Are the bigger trees older? Or is it just that these trees along the creek beds have better access to water?
Colin Tudge says that Salicoceae has about 400 species. They can be found in deserts, near coasts and beside glaciers.
Willows are full of surprises. Many species have 11, 12 or 19 chromosomes. But some have 224. The explanation is what biologists call polyploidism.
In humans, two individuals with 23 chromosomes provide egg and sperm that fuse to form a zygote. The haploid number for humans is 23. The diploid number is 46.
Sometimes, a chromosome doubles within a cell, but the cell doesn’t divide. That cell is a tetraploid. It’s rare in mammals but common in plants. The potatoes in your pantry are tetraploid versions of wild diploids.
Odd things can happen. A tetraploid crossing with a diploid yields a triploid. They’re sterile plants, meaning they must reproduce vegetatively. It’s why bananas have no seeds. Triploids double to hexaploids, which are fertile. Bread wheat is an example.
Willows tend to hybridize, and some hybrids are all one sex. Individuals are clones of the parent, reproducing from suckers. Is that a species? Every time I pass the big willow just north of the Commerce Street Bridge, I wonder if I could even tell you what a species is.
• Source: Colin Tudge, The Tree: A Natural History, 2006.
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