Random Cactus Generator

What the cactus generator does

You want a cactus. To buy, to draw, to put in a story, or because you have a windowsill and a vague sense that this is the one plant you cannot kill.

This gives you one. Pull a batch and you will get names like Living Rock, Old Man, Queen of the Night and Bishop's Cap, which tell you that people have been looking at these things for a very long time and running out of ways to describe them.

What follows is why a cactus looks like that. It is not a plant that gave up on being a plant. It is a plant that took every single part of itself and moved it somewhere else.

How to use it

1. Choose how many you want. One if you are picking, a handful if you are browsing.
2. Press Generate. A fresh set every time.
3. Press Copy to take the set with you.

A cactus breathes at night

Start with the problem, because everything else is the answer to it.

A plant has to open its pores to eat. There is no way around this. Carbon dioxide comes in through little mouths called stomata, and while those mouths are open, water goes out. Every plant on earth is stuck with that trade. Open up and eat, lose water. Stay shut and keep the water, starve.

Now put that plant in a desert at forty degrees. Opening up in the afternoon is not a trade. It is a death sentence.

So a cactus does something that sounds impossible. It eats in the dark.

All day the stomata stay clamped shut. Nothing goes in and almost nothing comes out. Then at night, when the air is cool and damp and the sun cannot take anything, the pores open and the plant takes in carbon dioxide. But there is no light at night, so it cannot use it. So it does not. It converts the carbon into malic acid and stockpiles it, holding it in the cells until morning.

Then the sun comes up, the pores lock shut again, and the plant breaks its own acid back down inside itself, releasing the carbon dioxide behind closed doors and running photosynthesis on it all day. Sealed shut, in full sun, running on last night's shopping.

It is called crassulacean acid metabolism, and here is the part I like most. It is not an abstraction. It means the plant is literally sourer at dawn than it is at dusk. The acid builds all night and gets spent all day. If you got up early and tasted a prickly pear pad and then tasted one at sunset, they would not taste the same, and that difference is the plant's breakfast.

There is a plant on your windowsill running a chemical battery on a twelve hour cycle, and it never once mentions it.

Every spine is a leaf

Now the second half of the trick.

Leaves are the problem. A leaf is a wide flat sheet built to catch light, and a wide flat sheet is also the best possible device for losing water to the air. In a desert, a leaf is a hole in the bucket.

So a cactus got rid of them. Not by dropping them. By turning them into something else.

The spines are the leaves. Same structure, same position on the stem, same developmental origin, rebuilt into a needle. That is why they come out of those little cushiony pads instead of anywhere on the plant. Those are areoles, and an areole is a compressed branch, so what you are actually looking at is a plant with hundreds of tiny branches all over it, each one having produced one very unhappy leaf.

And having thrown away the leaves, it needed somewhere to do the photosynthesis. So the stem took over. The green body of a cactus is not a trunk. It is the leaf, redistributed. It is fat because it is also the water tank, and ribbed because ribs let it swell after rain and shrink in drought without splitting, like an accordion.

So a cactus is a plant that turned its leaves into armour and its trunk into a leaf, and then learned to eat at night. Every strange thing about how it looks is one answer to one question, asked over and over for thirty million years.

The cactus that still has leaves

Pereskia is on this list, and if you saw one you would not believe it.

It is a leafy shrub. Sometimes a small tree. It has ordinary green leaves, wide and flat, growing off woody stems. It looks like something from a hedge in a wet country. It is a cactus. Fully, properly, cactus family, no argument.

There are seventeen species of them, and they matter enormously, because they sit at the very bottom of the cactus family tree. They are the closest thing we have to what a cactus looked like before it became a cactus.

Erika Edwards and Michael Donoghue went and measured seven of them in the wild in 2006, and what they found is the good part. Pereskia already handles water like a proper cactus does, despite having all its leaves still attached. The plumbing came first. The look came after.

Which reverses the story you would guess. The cactus did not become drought proof by losing its leaves. It was already drought proof, and then it lost its leaves, because at that point they were just costing money.

And Pereskia has the spines too. Growing out of areoles. On a leafy shrub. So you can stand in front of one plant and see the whole transformation held in one place, half done, still going.

If you see one in Africa, it is not one

Cacti are American. All of them, near enough. North, Central and South America, and one odd genus that made it to Africa and Sri Lanka, probably in a bird.

So what about the enormous spiny green columns all over Africa that look exactly like cacti?

Euphorbias. Not cacti. Not related to cacti in any useful sense. A completely separate family that hit the same desert problem on a different continent and independently arrived at the same answer. Fat green water storing stem, no leaves, spines, ribs, the lot.

Two lineages, two continents, no contact, same shape. That is convergent evolution, and there is no cleaner example of it anywhere in the plant world.

There is a tell, and it is a serious one. Break a cactus and you get clear watery sap. Break a euphorbia and you get thick white latex, and that latex is genuinely nasty. It burns skin and it can do real damage to an eye. People have taken a euphorbia home from a garden centre thinking it was a cactus, pruned it without gloves, and ended up in hospital.

Two other tells. Areoles, those little cushions the spines come out of, are a cactus thing and euphorbias do not have them. And euphorbia spines usually come in pairs sitting right on the stem surface, with nothing underneath.

So cactus is a family, but the cactus shape is not. The shape is just what the desert asks for, and two completely unrelated groups of plants heard the question and gave the same answer.

Where these come from

The cacti here come from a list our team put together and checked by hand. Press the button and one is drawn out of it at random.

That is the whole thing, and it runs on your own device.

The one mistake everybody makes

People say you cannot kill a cactus. People kill cacti constantly. They kill them the same way every time, and it is worth understanding why given everything above.

You are drowning it, not starving it. Almost every dead houseplant cactus died wet. The roots are built for a desert, which means shallow, fast, greedy roots that grab a downpour and then expect the ground to dry out completely within days. Leave them sitting in damp soil and they rot, and by the time the plant goes soft at the base it has been dead for weeks and nobody noticed, because a cactus is a water tank and a water tank looks fine for a long time after the pump stops.

Winter is not summer. A cactus in a cold dark room has essentially stopped. It is not using water. Watering it on the same schedule you used in July is the single most common way to kill one, and it kills more of them than neglect ever has.

The pot matters more than the plant. Drainage hole, gritty soil, and let it go bone dry between drinks. Get those three right and the plant will forgive nearly everything else you do.

Look back at the night breathing for a second and it all makes sense. This is an organism whose entire body plan is one long argument about water. Of course the way to kill it is to be generous.

Questions people ask

Is every succulent a cactus?

No, and it does not flip either. Succulent describes a habit, storing water in the tissue, and loads of unrelated families do it. Cactus is a family, Cactaceae, and membership is about ancestry. So every cactus is a succulent and most succulents are not cacti. The test that actually works is the areole. Little cushion, spines coming out of it, it is a cactus. Spines straight off the stem with no cushion, it is something else.

Why is the Moon Cactus two colours?

Because it is two plants. The bright red or orange ball on top is a mutant Gymnocalycium that cannot make chlorophyll at all. On its own it would starve in days. So it is cut and grafted onto a green cactus that does the eating for both of them, and the green bit at the bottom is a different species entirely. It is a plant on life support, sold as a novelty, and it usually dies when the host gives up rather than the top.

Is there really water inside a saguaro?

There is a great deal of it, and you should not go looking. The tissue is not a canteen, it is a slurry held in mucilage, and in many desert species it is alkaline enough to make you ill. The survival film version, where a man cuts a cactus and drinks, gets people hurt. There is also the small matter that harming a saguaro in Arizona is against the law, and they take it seriously.

Do they all flower?

Yes, and it is the thing nobody expects from a plant this severe. Cactus flowers are enormous, often silly, and frequently better than the flowers on plants that spend all year advertising. Queen of the Night, on this list, is the extreme case. It opens after dark, once, gives one night of it, and is finished by sunrise. If you own one you find yourself checking on a plant at midnight, which is not a thing you thought you would be doing when you bought a cactus.

How old is the big one at the garden centre?

Older than it looks, and this is worth knowing before you buy. Growth is measured in decades, not seasons. A saguaro takes something like a decade to reach the height of your hand and can be fifty or seventy years old before it puts out its first arm. The tall one in the pot is not a fast plant that got big. It is a slow plant that somebody waited on.

References

1. Edwards, E. J. and Donoghue, M. J. (2006). Pereskia and the origin of the cactus life-form. The American Naturalist, 167(6), 777 to 793. https://doi.org/10.1086/504605
2. Edwards, E. J., Nyffeler, R. and Donoghue, M. J. (2005). Basal cactus phylogeny: implications of Pereskia (Cactaceae) paraphyly for the transition to the cactus life form. American Journal of Botany, 92(7), 1177 to 1188. https://doi.org/10.3732/ajb.92.7.1177
3. Edwards, E. J. (2006). Correlated evolution of stem and leaf hydraulic traits in Pereskia (Cactaceae). New Phytologist, 172(3), 479 to 489. https://doi.org/10.1111/j.1469-8137.2006.01850.x
4. Winter, K. (2019). Ecophysiology of constitutive and facultative CAM photosynthesis. Journal of Experimental Botany, 70(22), 6495 to 6508. https://doi.org/10.1093/jxb/erz002