Spindly

Posted On September 16, 2021

While nature contains great and fascinating variety, the basic underlying system is almost always the same: plants can turn sunshine into sugar but they can’t reproduce without help. So they offer the sugar to anyone in a position to move sperm to egg and then to disburse the resulting babies to new spots so they can get on with getting on.

To accomplish the first step, flowering plants offer nectar and arrange for those who indulge to also gather a little pollen (which produces the male reproductive cell). The flower’s female structures are positioned so that visitors bearing pollen brush against the stigma (outer girly part) and if the pollen is from the same species, hey presto, things get going.

I have written and spoken about pollination hundreds of times. But I haven’t paid much attention to what takes place after fertilization.

I noticed this deficiency thanks to a bunch of spindle trees (Euonymus europaeus), growing in my New Hampshire yard. They have weird dangling things (the photo at the top of the post) that reminded me of something very familiar that I couldn’t put my finger on.

I started with what I knew, which was that these were likely seeds. Then I ran into my ignorance. I had no idea how plants made fruit and seeds. I knew a great deal about pollination, but my interest always ended when the bee or butterfly went away. Turns out, the seed/fruit story is very complicated and while trying to ease my confusion, I had an insight. I might not have a scientific understanding of how plants set seeds and make fruit, but I had tons of experience dissecting fruits and vegetables. We all do. It’s called eating.

We make distinctions between fruits and vegetables based on their sugar content. If it’s sweet, we call it fruit, if it’s not sweet, we call it a vegetable. This distinction is irrelevant, except to us. If if has seeds, it’s fruit.

We eat a lot of fruit. Green peppers are fruit, tomatoes are fruit, figs are fruit. Making use of this lifetime familiarity with plant reproductive structures, I can say with confidence that there are a bunch of basic fruit types that can be categorized by how the seeds are distributed within the fruit.

You have the basic single-seed variety. Think peach. With any peach, you have skin, inside of which is tasty flesh, inside of which is this pit that is really interesting and rock hard and which contains something that looks like an almond.

Since peaches have only one ovary per blossom and one egg per ovary, each peach has only one seed that we call a pit. When the egg got fertilized within the blossom, the plant produced a baby (which was that almond-looking thing you bit into probably more than once during your childhood). Everything else was wrapping paper and payment for transport.

The wrapping paper is the fuzzy skin. It keeps the juicy insides from drying out. It’s important that those insides stay as juicy and sweet as possible because they are the payment to the stork (or deer, or squirrel, or person) who will carry the dear baby, carefully packed into a hard outer shell that most animals other than children won’t bother to open twice. 

Peaches, are really basic. Just the one pit. But what about apples? They have 5 to 7 seeds inside a moderately hard plastic case that we call the core. And no, it’s not plastic.

Translating into plant terms. The apple had more than one ovule in the ovary, each of which had an egg, that was found by appropriate pollen. The plant set one seed per ovule, spun a bunch of tasty fruit around it and covered it in a waxy wrapping to keep the whole thing fresh for you.

The reality of this is so much more complicated than my very simple explanation but it will suffice for now.

The core we toss away contains the whole egg sac and it had a placenta from the mother plant to nourish the seed as it grew. The stem of the apple is the same stem that held the original flower to the branch. At the other end is that kind of dried up crown. Those were the flower’s stamens (the stiff, thread-like structures in the middle of a flower that wave the pollen around).

Another familiar fruit system is when the plant has multiple ovules that stretch down the length of the plant in one or more spiraling chambers. This sounds so complex my mind couldn’t grasp it until I realized that article I was reading was describing a cucumber. When you prepare one for salad, you often scoop out all the seeds (and that gelatinous stuff surrounding them). Again, ovules, seeds, placenta. And again, stem at one end, remnant stamens at the other.

Grapes have their own schtick and for each variety, you have to decide whether to eat the seeds (and skin) or spit them out. Farmers have grown grapes with seeds so small you can’t even feel them so that we may enjoy seedless grapes. But still, a flower got fertilized and seeds got set or there wouldn’t have been any fruit in the first place. 

The plant is going through all this trouble to make sure that someone, anyone really, eats the damned thing and poops out the seeds somewhere else.

I have spent the last few days contemplating fruit because I cannot understand why the spindle trees make such weird seeds. They are shaped like the seed capsules of a various fruits, but without the fruit around them. Kind of like a hairless cat. It takes a minute to get oriented.

In illustrations of plant anatomy, early botanists made use of a very stylized mode of drawing like that apple image above. They weren’t so much trying to capture in paint the essence an actual piece fruit. They were trying to draw the Platonic ideal of a particular plant. Think bird guide. A bird in the wild doesn’t really look like the picture in the guide, but guides that rely on photographs are too confusing. So what you end up with is a stylized drawing of the subject, with all the different parts very clearly delineated. 

When these images turn to fruit, they show detailed cross sections. That’s what triggered me on the spindle seeds.

Imagine you could lift the whole apple seed capsule out for closer examination. Isn’t that pretty much what the seed capsule of spindles look like. They look like fruit without the fruit.

In this cross section photo of the spindle seed capsule, you can see the orange fleshy fruit (not the pinkish casing, that orange flesh around the white pith with that small green line in the middle, which is, I think, the developing seed. They won’t be ripe for a few more months.

I easily identified the plant as a spindle tree through iNaturalist. And, while it isn’t native, it is almost identical to a midwestern native Euonymus atropurpureous, which has the wonderful common name of Wahoo. Basically, the two are so similar that the only way to tell them apart is blossom color (the native one having purple flowers, which is what atropurpureous means in Latin).

Even more in common, they are both named for what you make from their incredibly strong but flexible wood. In Europe, this wood was used for making spindles, resulting in the name “spindle” for the shrubby tree.  “Wahoo” is a Dakota word that means “arrow wood,” because the wood was used for making arrows. So in both cases, the name is basically a utilitarian label.

It was disappointing that the first thing I am writing about in my new home is not native. At first, I thought this plant was listed as invasive by my new state, New Hampshire; it is shown as such by a map from invasive.org. But a consultation with the list of prohibited plants published by New Hampshire does not list this plant, so hooray! It’s not dangerous, merely not from here.

A word on natives, non-natives, and invasives

When a plant is considered a native, we basically mean it evolved in place. Everything evolves by rubbing up against everything else and if a plant or animal is well suited to the environment, it will thrive, if it is not well adapted, it will tend to die out.

Things that are good at finding food and not becoming food themselves tend to reproduce and fill the world. 

The result is a natural world that is wonderfully in balance with eaters and eaten matching up in strong enough populations to survive one another. The reason this happens is that it more or less has to. That’s what evolution consists of. Things perpetually seeking a balance. 

If a new mutation arises, it either confers an advantage, a disadvantage or it is irrelevant. If it confers an advantage, it is likely that it will survive the generations. If it confers a disadvantage, those who carry the gene will be less successful reproducing and will tend to dwindle. If it is irrelevant, it just gets carried along until perhaps one day it does make a difference.

This is how the world rolled along forever until we showed up. 

Human beings are endlessly curious and endlessly peripatetic; we have spread everything here and there as we have gone along. Sometimes we bring a new plant or animal to a place where it has never been before. That plant, happy or miserable in its new location, is a non-native. It’s there not because it evolved there but because we put it there. 

Sometimes, this works out great and the new plant or critter settles in like it had always been there. It becomes a new neighbor with plenty to offer. It’s not native, but it’s not causing any real trouble for the natives who evolved to live in that place.

But too often, you end up with the bad scenario. We move something somewhere that is so absolutely fabulous, so incredibly awesome that this thing has never had it so good. Whatever once ate and bothered this winner is missing in this new place. In the new place, the temperature never gets hot enough or cold enough to kill this thing. It has found nirvana.

We call this one invasive because it can reproduce so fast that other things that did evolve in place can no longer find enough food or soil nutrients to survive. Their populations dwindle as this new individual defeats all the competition and, fat and happy, controls the world.

The native wahoo is not in range in New Hampshire, so it isn’t really being crowded out by the spindle, but maybe there is something else about it more noxious than I realize that earned it the sobriquet “invasive.”

While I don’t know how dangerous spindle trees are to the balance of nature here, I do know that they present a real danger to anyone foolish enough to eat one of those berries. They are very toxic. In a quick perusal of the Internet, I couldn’t find any reference to animals eating the berries or leaves, but in England, where they are native, they are apparently well used by wildlife.

If you eat a few, you are likely to visit the bathroom rather frequently the rest of the day. If you eat more than 30, you might end up dead. In fact, carpenters who worked with spindle wood have been known to fall sick from simply handling it. All parts of this plant are toxic.

And who says naturalists don’t live on the edge!