Pereskia and the Origin of the Cactus Life-Form

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cortez753
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Pereskia and the Origin of the Cactus Life-Form

Post by cortez753 »

Interesting article from The American Naturalist 2006.

http://phylodiversity.net/donoghue/publ ... rNat06.pdf
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cortez753
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by cortez753 »

I have a theory. What if Pereskia is adapting OUT of the cactus life style? :-k
DaveW
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by DaveW »

Or are cacti adapting out from Anacampseros! :lol:

http://www.pubfacts.com/detail/21642211 ... ochondrial" onclick="window.open(this.href);return false;

http://www.academia.edu/5302361/Phyloge ... tyledoneae_" onclick="window.open(this.href);return false;
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Saxicola
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by Saxicola »

I want to say a lot about this (I'm a plant taxonomist by training and this is right up my alley) but I'm going to keep my remarks fairly brief because I don't like discussing this with my hands tied. For example, this website blocks the "E" word. See the bottom part of this page to understand what I'm talking about: http://cactiguide.com/aboutme/" onclick="window.open(this.href);return false;

In short, it is likely the original cacti were something similar to Pereskia and Rhodocactus, but it is not guaranteed that they were them. He makes a strange statement near the end that the close relationship with Portulacaceae helps prove early cacti were leafy shrubs. Portulacaceae are leaf succulents (whereas most cacti are stem succulents), but most of that family are succulent herbs. So to me it is more likely the earliest cacti were herbs that developed into shrubs that then developed succulent stems and reduced leaves.

By the way, the closest relatives are Portulacaceae and things like Anacampseros, but take a step or two further back and you will see that Dideriaceae and Aizoaceae are related as well. More surprisingly some other cousins of cacti are Carnations, Bougainvillea, and even carnivorous plants!

Cortez, your hypothesis is theoretically possible but from a scientific standpoint is much harder to explain given what we know than it is to go from a semi succulent shrub into the cacti we normally think of. That being said, I believe that Pereskiopsis is an example of a cactus trying to return to a leafy habit.
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by A. Dean Stock »

Saxicola, thanks for a very concise, well presented appraisal. My reply was going to be at least two paragraphs longer and not as good.
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Re: Pereskia and the Origin of the Cactus Life-Form

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Ev0lution can in a way reverse itself, therefore you can never claim it can only progress in one direction. Some creatures that came out of the sea and became land animals with legs have later returned to the sea again largely loosing them:-

http://www.earthmagazine.org/article/ho ... turned-sea" onclick="window.open(this.href);return false;
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by Saxicola »

Definitely Dave, but from a scientific standpoint you start with the simplest explanation for a phenomenon and then adjust or correct that assumption based on additional evidence. So I won't dismiss the possibility that the original cactus was more succulent and that the Pereskioid habit was something of an anomalous reversion to a more "normal" plant form, but nothing in the genetic evidence or the sparse fossil record provides support for that idea. Also, taxa can reach the point in their, lets say "Alfred Wallace style development", that it is all but impossible to revert back. For example I see no way a cactus could make the floral changes necessary to produce something that replicates an Aloe flower in the fine details.

A. Dean, thanks for the compliment. I do get the occasional moments of lucidity that interrupt my ramblings!
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Re: Pereskia and the Origin of the Cactus Life-Form

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I don't think there is any fossil evidence for the Cactaceae anyway is there? Eopuntia douglasii has later been claimed to be a fossil sedge like rootstock if I remember correctly, not an ancient Opuntia,

"Thus the fossil record for cacti is poor, or in fact absent. In 1944, a presumed fossil cactus "Eopuntia douglasii" was described from Eocene deposits in Utah. There was much controversy over whether this compression fossil was indeed a cactus, and after significant bantering about the literature, most people do not believe this "fossil" is indeed a cactus."

http://www.google.co.uk/url?sa=t&rct=j& ... oH5rcreBwA" onclick="window.open(this.href);return false;

http://www.jstor.org/discover/10.2307/2 ... 5154377153" onclick="window.open(this.href);return false;
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Re: Pereskia and the Origin of the Cactus Life-Form

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Any pictures of the fossil?
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by cortez753 »

Yes the Cactaceae fossil record is very limited. But what about other succulent taxa like Euphorbiaceae. Is there any fossil evidence there that shows a reversion from a succulent to a non succulent life style?


This 2008 article says that much more research needs to be done on reverse succulence.
Last section. The Road To Succulence: A One Way Street?

http://www.brown.edu/Research/Edwards_L ... asel08.pdf
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Re: Pereskia and the Origin of the Cactus Life-Form

Post by BobbyZ »

I enjoyed a paper on the development of cacti based on the physiological models of water stress strategies not just a DNA based phylogenic relationship. I only skimmed over the manuscript and have much to read into its implications as you guys did. Hey my plant physiology water relations course at UCR was some 35 years ago. I would like to thank Yall for making this availabl and open to discussion. Saxicola I like your idea of Persekiopsis as being a cactus attempting to revert back to a shrub. Before I knew it was an Opuntoides I thought it was a Persekia. Now I hope my Barbados gooseberry (Persekia aculeata) gets established in NE Florida so I can eat them berries.
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Re: Pereskia and the Origin of the Cactus Life-Form

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"Sparse fossil record" was my fancy way of saying "I'm not sure what fossil evidence there is for cacti but I'm sure it isn't much if any". This link: http://www.ucmp.berkeley.edu/anthophyta ... lidfr.html" onclick="window.open(this.href);return false;
suggests the only confirmed Cactaceae fossils are scraps in sloth dung. Even if we had good fossils it might not tell us much. There are virtually no fossils of extinct fossil plants that don't cleanly fall into one of the plant families we have today. The ones that do exist mostly tell us about the very earliest flowering plants, not the more advanced groups. What would be really interesting is a fossil of a pre-cactus. Something not quite a cactus and not quite a Portulacaceae or Anacampseros either.

Bobby, physiolgy is critical to understanding why plants look like they do. Historical relationships will give you the basic ground plan for a plant to work with, but the environment it is in and how a plant reacts to it, over time, will affect how a species develops. Cacti became fat stemmed spiny succulents because it was the best way it had, given its genetic makeup, to survive in a harsh climate. But now that they are fat stemmed succulents any future development will have to work with that body plan as you can't magically make it go away.
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Re: Pereskia and the Origin of the Cactus Life-Form

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The only good cactus fossils available are only mid to late Pleistocene, at the oldest, and we only have them because of the habits of wood rats, sloths, etc. The entire family is relatively recent in origin and its members seldom very common compared to say grasses, forest trees, etc. so we have little to go on. Fortunately, DNA studies can provide some good estimates of the time relationships between major taxa.
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