Every morning I drive by a string of globe willows by an apartment complex a couple blocks from my office. For the past 2 weeks, they’ve been showing hints of green, and I thought I should take a closer look. So yesterday at lunch I walked over to the apartment complex, camera-phone in hand (I have got to start taking my real camera with me everywhere if this blog thing is going to work), entered the parking lot through a hole in the fence, and checked out the willows.
Tangent: My father put my siblings and me through college largely by buying, fixing up and flipping slightly run-down apartments in various lower-middle class suburbs around
As a kid in
Peking Willow (Salix Babylonica) from
There are somewhere between 350 and 400 species of willow in the world. Many look very similar and many hybridize freely, which means that a) nobody can agree on how many species there really are, and b) they’re tough to tell apart.
Most willows I’ve been familiar with as an adult have been the brushy kind that grow in canyon bottoms and whack you in the face as you’re trying to bushwhack- one nearly put my right eye out in a side canyon of the Dirty Devil River (pictured) in 2001.
There’s a stand of willow- maybe Coyote Willow (Salix Exigua)- along my usual morning mtn bike route, at the mouth of Dry Creek, which is still completely brown. (Photographed this morning… photo not saved on hated camera-phone…)
But down in the valley, the Globe Willows are coming to life. Globe Willows seems to show green so early, because the very twigs turn green even before the buds start to bloom. In this shot here you can see the strong green tint if the twig bark, as well as the now active (green) leaf buds bursting from the older (brown) bud sheaths which covered the juvenile, then-dormant buds over the winter.
I haven’t been able to find out about the green bark, but I wonder
if this is an adaptive advantage of photosynthesizing via chlorophyll directly in the bark, getting a pre-bloom jump on growth, through a mechanism similar to Palo Verde, for example.
So other than there being lots of them and some turning green early, what’s so great about willows? Here’s what: Pollination.
Willows, like all flowering plants, are angiosperms. It’s thought that all angiosperms descended from a common ancestor. There’s a lot of background behind this consensus, but the Reader’s Digest version (I haven’t seen a “Reader’s Digest” since about 4th grade- do they still exist?) is that the way in which angiosperms reproduce is so phenomenally complicated and bizarre (and I’ll cover it in a future post) that it seems terribly unlikely to have evolved more than once.
It’s also thought that this common angiosperm ancestor was insect-pollinated. Today, many angiosperms are insect-pollinated, and many are wind-pollinated. Overwhelmingly, the wind-pollinated angiosperms- including aspens, cottonwoods, oaks, maples, beeches- have really lame-looking flowers, while all the plants with spectacular-looking flowers- orchids, roses, cherry trees- are insect (or bird or bat) pollinated, the thinking being that if you don’t have to attract a bee or a hummingbird, why spend so much energy growing a showy flower? But even in the lame-o wind-pollinated flowers, there are remnants of the showier, more extravagant flower-structures (petals, etc.) that hint at a glitzier, insect-pollinated past. So modern oaks for instance, apparently descended from insect-pollinated ancestors who for whatever reason later abandoned insect-pollination for the wind-pollination of their ancient, ancient, ancient gymnosperm ancestors.
Willows are dioecious, meaning that a given plant will have either all male or all female flowers, but not both. But male or female, their flowers are pretty lame (see diagram.)
And because they’re so lame, it was assumed for a long time that willows were wind-pollinated. But it turns out that they’re in fact insect-pollinated, and that apparently, they went through an evolutionary-pollination-strategy-story (EPSS?) that went something like this:
Ancient, ancient wind-pollinated gymnosperm ancestor evolved to…
Ancient common insect-pollinated angiosperm ancestor evolved to…
Ancient wind-pollinated ancestor of Salicae family (willow and poplars) evolved to…
Modern insect-pollinated willows.
Which means that willows have switched between wind and insect pollination at least 3 times. This is what’s so cool about plants; every plant tells a story, and the more you know about plants, and better understand their stories, the better you can see the Beauty of the World.