Rarest and most common cactus?

[habanerocat]

A simple question I've been asked a few times and I've struggled to give a definite correct answer.

Perhaps we can only guess. Any ideas?

[anders]

In cultivation or in the wild?

[DaveW]

It can depend country to country. Some plants are more easily available in some countries than others. Some formally common plants are now tending to become rarer in UK cultivation as collectors turf them out to make way for the latest novelty. Also when that happens nurserymen stop propagating them. When you loose a plant after 10 years or so, you often have a job finding a nurseryman that stocks a replacement, even though it was quite commonly grown originally.

The rarest is usually the one that has just been discovered, or is hardest to grow. Really the rare ones are the ones you are finding hardest to obtain, but that can change year to year.

[habanerocat]

In cultivation or in the wild?

The general question relates to both. The total sum worldwide.

[KarlR]

Maybe Yavia? Or perhaps one of the small Mexican species restricted to only the one hill, like Pediocactus knowltonii is in the US. Probably some obscure epiphyte or columnar which nobody grows though

[Keith H]

Most common has to be the Opuntias that you see growing wild every where as unwanted invaders from the Mediteranian to Austrailia, and giveing them a close run for the money the Agaves they almost always grow along side of.

[Alejandro]

In cultivation, Echinocactus grussonii has to be one of the most common

[Eric Williams]

As a matter of interest I have a cristate Yavia cript. and a football size E grussonia. I really prefer the latter plant as I grew it from seed. Cheers

[Tina]

Rarest - maybe cristate ariocarpus kotscheybeyanus or cristate ariocarpus fissuartus on it's own roots.
I have seen two cristate ariocarpus retusus so not so rare but I have never seen the other two in cultivation, although I did get offered one for £3000

[DaveW]

In habitat nobody can really be sure what is the rarest plant, or even if it is now extinct. They can only say they did not find it at the type locality, or the site previously reported. With some cryptic cacti such as Thelocephala's they can remain underground for years until rains come, then they can appear in their hundreds when flowering makes them obvious.

I remember reading years ago a report where a professional botanist visited a habitat of one of the small Ariocarpus and could not find any, therefore declared they were extinct at that locality. A year or two later another botanist visited the same site after rains and found them flowering in their hundreds, having reappeared from underground.

Backeberg originally reported a Browningia as rare. Evidently if he had gone over a few more hills they were quite plentiful since he had only encountered a few outliers of the population. With cacti it is often a case of "we only found it here but nobody knows what's on the next hill, since nobody has yet climbed it in search of plants."

With the exceptional rains in Chile in 2015 a plant originally described decades ago by Philippi (not a cactus) reappeared which had not been seen since his days. All botanists can truthfully say is not that a plant is rare or extinct, but they did not find it again when they looked.

Some plants, even some cactus species, may die out as plants when conditions are too extreme and pass part of their lifespan as un-germinated seed, which may regenerate the population again when suitable conditions return. Such situations may exceed our human life spans, therefore they may be "extinct" as far as our generations are concerned, but future ones may rediscover they are quite plentiful again. It is never scientific to be categorical, science can only disprove, never 100% prove and botany is supposedly a science.