Why do Echinopsis cacti have so many synonyms?

For example, I've seen the same cactus labeled as Trichocereus grandiflorus, Lobivia grandiflora, Helianthocereus grandiflorus, Trichocereus rowleyi, Cereus huascha, Trichocereus huascha, and Echinopsis huascha (which I think is the most current?). Are all of these the same plant species?

Part of me wonders if the taxonomists involved weren't taking mescaline.

Edit: I also found this list from another source:

Echinopsis pecheretiana, Trichocereus grandiflorus, Lobivia hyalacantha, Acanthocalycium hyalacanthum, Helianthocereus hyalacanthus, Echinopsis hyalacantha, Pseudolobivia pelecyrhachis var. lobivioides, Trichocereus lobivioides, Helianthocereus pecheretianus, Trichocereus huascha var. pecheretianus, Lobivia purpureominiata, Echinopsis rowleyi, Chamaecereus grandiflorus, Echinopsis lobivioides, Trichocereus andalgalensis, Pseudolobivia lobivioides, Lobivia huascha, Cereus andalgalensis, Helianthocereus andalgalensis, Lobivia andalgalensis, Helianthocereus huascha var. auricolor, Trichocereus auricolor, Trichocereus andalgalensis var. auricolor, Trichocereus catamarcensis & Helianthocereus huascha.

And this is for just ONE species out of probably thousands.......why?

Acanthocalycium is somewhat referred to as a separate genus, helianthocereus is often placed in trihocereus, the difference is trihocereus tends to have night white flowers, while helianthocereus is usually with day color flowers. They are columnar subgenuses of echinopsis. Pseudolobivia refers to plants whose stems look like echinopsis/trihocereus, while lobivia means smaller plants, with curved spines. Except for most ferox and mammilosa, pseudolobivia have color flowers. Echinopsis have white or pale pink flowes. Chamaecereus was thought tobe a separe genus because it doesnt look its relatives in shape and habitat. Some even clump setiechinopsis mirabilis under echinopsis.

All these synonyms reflect a long history of these plants being reclassified either with one genus or another, split again etc.
Most recently it was determined many of the Echinopsis, Lobivia, Trichocereus and a few other genuses all should be Echinopsis xxxxxx. Mainly because genetically they had more in common than not. However, as skopjecollection already points out, to most people growing these plans there are many more obvious differences than there are similarities, yes their flowers show similarities as do their spines a bit, but one is a towering arborescent giant whereas others are small globular plants.
I am not sure when exactly, but in response to this study further work has determined that if they do this lumping they really should be lumping just about every south American cactus into one big genus (presumably 'Cereus' as I think that is how many of the south American cacti were first described), which makes sense to very few people, so I have read that there is a movement to split many/all of these up again.

According to the most recent edition of the the New Cactus Lexicon Echinopsis terscheckii should be Trichocereus terscheckii again. They have Echinopsis huasha under Lobivia...

It is a mess...

I think they all kinda belong together, but should be split up in subgenuses. While the difference between a lobivia and a trichoereus pachanoi is clear as night and day, the diffrence between terschekii and formosa not so much.....

mcvansoest said:further work has determined that if they do this lumping they really should be lumping just about every south American cactus into one big genus (presumably 'Cereus' as I think that is how many of the south American cacti were first described), which makes sense to very few people

So does this even include rainforest cacti? I'm under the impression that the majority of South America is rainforest...

Ive had this debate before, so in a nutshell , no. Most south american cacti come from
-attacama desert(copiapoa, eulychinia)
-mountainous savannas (like cleistocactus and some trihocereus)
-patagonia (maihuenia, austrocactus)
-brazilian savanna(, pilosocereus)

When you say "most" how do you calculate that? I'm just curious if you use number of species, number of genera, or some other criteria. Because I've had trouble even finding how many genera (or species) there are, so if that's what you use, how do you use it?

The fact that they blend together so easily doesn't help things, I'd imagine.

Most genus over geographical distribution i guess. And most numerous/famous/collected,

Dont bother learning all the genuses and species, chances are that youll never even see some, while some are overabundant(im blaming mammilaria). Pretty much all the good ones are already cultivated.

I don't see them only in cultivation though. When I go to Argentina and Chile it's helpful to know what I'm seeing. They all blend together for me and because of the fact that nobody can seem to accurately count them or name them, it's appearing more and more like they do for taxonomists too.

That's why I think it's useless to say "most" to mean those growing in deserts or grasslands. It's an imprecise and even misleading way to categorize them that makes the situation even more confusing.

Youre not going to find a rhipsalis growing near a salf flat, and youre not going find a trichocereus pascana growing in a tree canopy. Iding species for genuses like echinpsis(sub lobivia), parodia, rebutia ,eriosyce,mammilaria is hard. I dont think there are a lot of people that know each one in habitat, but those that do, 80% chances are they are scientifically engaged in cactus studies,
The other ones are either master growers or poachers. You could allways take photos and look them up on the web .

If you ask me, best way to classify cacti? Genetic comparison. Might be annoying, might be practical. But is probably the most scientifically accurate method, rather than convenient- which is the annoying part about lumping everything from south america under cereus.

That's actually why I'm planning on going--to photograph them. But my timeline keeps getting pushed back, so I was reading about them and came across this absurd level of confusion. It would make sense if the confusion was just among us "laypeople" but it's not. It seems even worse (in some ways) among the scientists studying them. lol

skopjecollection said:If you ask me, best way to classify cacti? Genetic comparison. Might be annoying, might be practical. But is probably the most scientifically accurate method, rather than convenient- which is the annoying part about lumping everything from south america under cereus.

But genetic analysis does not necessarily say much about relationships in plants--at least not as much in animals. Remember that plants can and do reproduce vegetatively so if one plant has five offsets and each offset has 5 offsets and each of those has 5, and so on, in a couple hundred years you could have tons of plants with much less genetic variability than those which had reproduced sexually during that same time period. So you cannot calculate genetic relationships based on DNA the way you can in animals (who reproduce only sexually so there's a more linear method of measurement across time).

Yeah, well dna evidence suggests that a portion of rebutia is related to browningia hertlighiana, who in turn is not related to the tribe browningiae.

My point(you posted before i did)? is that its still the only reliable method of telling plants appart now. Dont think people have found fossilized cacti, so we can only assume that the most primitive ones(because lets compare them to other flowering plants, the oldest is magnolia) looked like perserkia, and in turn split up into quiabentia->cylyindropuntia->browningia+opunrtia or maihuenia->grusonia->ferocactus. These are only loose speculations based on similarity, but at the core of it, some evidence does indicate some similar modifications over time. The other method of classification is ocular, and well, euphorbia would have been considered a cactus if that were the case.......

Well, there are a few fossilized cacti from what I remember. I know at least one ancient Opuntia-type was found in modern Utah. Regular Opuntias still grow there and it's a beautiful sight to see them sprawling out across the cold desert. I'd live there if it were easier to move there.

I dont live in the us, (just hope you dont think less of me), nor have i visited any "proper" cactus habitat. We do have , however, an invasive opuntia humifusa in some regions, and in neighboring countries there are populations of bushy opuntias, hardy cilindropuntia, agaves , carpobrotus and etc. Dont know when the cacti came here, but they are here to stay..... have a nice tour btw.

Oh, not at all! The fact that you can spell (and probably pronounce) all of these genera means I think more of you! I can't do either!

I live in a part of the US which is a temperate near-rainforest and we have only native species of cactus (also an Opuntia). There are parts which have 0, too.

I can spell as good as my fingers can type, so not 100% accurately. I do use spell check out of laziness , and spell check made me a lot more lazy in turn. I studied engilsh for quite a while, and with some recognition too. But not really the point, as the names are latin, and ive only managed to study the genuses ( and a few species) i wanted to collect. it was not the most fruitful of endeavors, since some plants had issues.... I do take cactus collection seriously however, as got tired of my failures( echinopsis, parodia, rebutia, jungle cacti died on me... even had a few lepisimiums that didnt make it). So i had to study cactus growing hard .