Sciency Answer: Variegated plants are liars

Dear Mister Greensparrow Gardens Person:

I have a SCIENCE QUESTION (dah duhduh DAAAH) about variegation. Isn't the point of a plant being green for good light wavelength absorbency? I mean, plants that are other colors besides green still absorb most of the spectrum because of different kinds of chlorophyll, etc. But what about the plants that are variegated to have mainly white leaves? What is up with that? Doesn't the color "white" mean that all the wavelengths are reflected back? So how would they photosynthesize properly if they couldn't trap light efficiently? With some of these plants, there is still some green or other color, but it doesn't seem like it would be enough to support such a big plant. 

-Hannah

You are absolutely right -- completely white sectors on leaves don't photosynthesize, and plants that produce whiter leaves are going to be inherently less vigorous than ones with green leaves. So why are they like that?

Most variegated plants are essentially man-made -- they are unhealthy, mutant freaks that would die if we didn't like them and keep them alive in our gardens. Sort of like chihuahuas (except chihuahuas are disgusting and variegated plants are delightful.) Surprisingly, however, some wild plants, like some caladium, begonia, and dieffenbachia naturally have white patches on their leaves. Breeding has increased the amount of white on the plants we grow, but still, the wild plant have distinct white patches on their leaves. Why?

Because they are liars.

Imagine for a moment that you are a expecting mommy-to-be leaf miner. You are flying about, looking for a good leaf on which to lay your eggs so your babies can happily start eating away at them. First you see a leaf like this:

photo credit

This leaf is already infested with leaf miners. Lay your eggs on that leaf, and your babies will starve, because there isn't enough leaf to go around. So you keep flying, and see a healthy, green leaf like this:

This looks perfect! You land, and lay some of your eggs, and then happily fly on to find a home for the rest of your brood. But the next leaf you see looks like this:

photo credit

This leaf looks TERRIBLE! There must be a million leaf miners and caterpillars already there, munching away for this leaf to have so little green on it. So you fly on... fooled by a sneaky, variegated plant. The plant has made a trade off: less efficient photosynthesis in exchange for not being eaten alive.

In other words, natural leaf variegation is the plant equivalent of pretending you have whiplash in order to get insurance money. This is a fact that should make those of you who don't like variegated plants because they look unhealthy rethink your position. That is just what those plants WANT you to think! You are being fooled, just like the little leaf miners. Go buy some today just to show those plants you are smarter than them.

If you want more of the science behind white leaves, here are some good papers (subscriptions required):
The history of research on white-green variegated plants
Ecology of a leaf color polymorphism in a tropical forest species
Leaf variegation in Caladium steudnerifolium (Araceae): a case of mimicry?

Have a question? Get a sciency answer! Just e-mail me: engeizuki at gmail dot com

More caterpillars eaten alive

I love wasps. I love them even more when they are killing caterpillars. Which was why I was excited to see this:

It is a tomato horn worm -- bane of the tomato growers existence -- covered with the pupal of a tiny little parasitoid wasp. A momma wasp finds a tomato horn worm, and cheerfully lays some eggs inside it. The little baby wasp larva hatch and happily munch on the innards of the caterpillar. Like all good parasitoids, they are careful to save the vital organs for last so the caterpillar doesn't die. Finally, they wriggle their way out of the body of the horn worm, build a little pupa (the white things in the picture) and transform themselves into lovely little adult wasps.
So so cool... Parasitoid wasps are the best. There are tons of different kinds -- some of which are so tiny they actually lay their eggs and grow up inside aphids!

Chair/pantry for wasp babies

I was sitting on my front porch when I noticed a little wasp hoving about in an annoyed manner. I got up, and she quickly landed on my chair and started poking around in the little decorative holes drilled in the wood.

 What is she up to?

 Oh, just shoving a live, but paralyzed, catepillar into one of the holes.

 All finished now -- she flies off. Probably to get another catepillar. When the hole if full, she cap it with mud, as you can see she's already done with several of the other holes in the chair.

Before she caps them, though, she'll lay some eggs. They'll hatch into little baby wasps, which will munch happily on the still living, but paralyzed caterpillars -- they carefully eat the vital organs last, so the catepillars don't die and start rotting.

Kind of gruesome, but mostly cool... besides, I think those caterpillars had been munching on my roses, so they deserve to be eaten alive by wasp larvae.

Borer resistant zucchini

Back in January, I talked about trying a new type of zucchini in my garden this year. Normally I grow the variety 'Costata Romanesco' because it is simply delicious -- but, like all zucchini I have grown, it generally collapses sometime in the middle of the summer due to attacks by the evil squash vine borers.
So this year, along with my 'Costata Romanesco' I'm growing 'Zucchetta rampicante tromboncino'. It is a different species (Cucurbita moschata rather than the typical summer squash Cucurbita pepo) and is supposed to be resistant to borers.


I can't speak to the borer resistance, at least not yet, because so far none of my squash have been attacked. I'm sure it is coming, though... borers being the evil little vermin they are. But I can speak to their other attributes. They are very late, and low yielding compared to any other zucchini I have grown -- they started several weeks after my other zucchini, and I've only picked 4 of them so far. I wouldn't recommend them for a small garden, unless you grow them up a trellis, because the vines are very long and vigorous -- a good dozen feet long so far, and showing no signs of stopping.

Here are what the fruit themselves look like. My standard Romanesco is on top, and the Tromboncino is on the bottom.

 Here they are sliced, ready to go into a pan with some hot olive oil and fresh tomatoes.


The flavor is quite good, though different from a standard zucchini. My romanescos have a warm, nutty flavor that I adore. The Tromboncinos have a sweeter flavor that reminds me a little of a winter squash. Raw, the Tromboncinos are firmer, drier, and crisper than the romanescos, but when cooked, they were slightly more inclined to get mushy -- which is not a good thing, as mushy zucchini is foul and loathsome.


All in all, I like the tromboncinos, but I'm not in love with them. They are beautiful and interesting, and the promise that they'll keep on producing all summer even if borers arrive is certainly wonderful. I plan on growing them again next year, along side my standard zucchinis -- as a standby for when the borers decided to try and ruin my summer.

Wednesday links: Mostly about bugs (and other stuff)

This week, we're starting with some links about the beauties of are arthropod friends:

Pam has some lovely shots of a just emerged adult cicada. The wings are so delicate, and so beautiful.

Frances does an outstanding photo essay on the beauties of spider webs. And even one (I think) exceptionally attractive spider.

Keeping with the entomological theme, I am indebted to Allen Becker for finding out about this fascinating study. The actual study is a lot of chemistry that is way over my head, but the take home message is pretty simple: air pollution, especially ozone, can destroy the fragrance of flowers. This is sad for the gardener, but very sad for pollinators like bees who use floral scents to find their food. Yet another reason to bike to work!

Moving on to less pretty matters, there is a legal battle underway in Europe over patenting of genes in broccoli and tomato. An interesting and very complex issue. If you are really into this stuff, this is a clear (if not particularly exciting) explanation of the various forms of intellectual property protection available for plant varieties -- specifically in Europe. The US patent system is a little different -- I think. I get confused about it all, which is mostly why I'm reading and linking to these things.