Brasiliopuntia brasiliensis

[Greenlarry]

From what I read in a excellent cacti book Pereskia and its clans came first then the Opuntiads then a seperate branch formed in a forest environment which led to the typical epiphytic cacti

[DaveW]

The concept of primitive and highly evolved is always controversial. The plants you see today are the ends of their present lines of evolution, not links in a chain of evolution. Somebody once described the present situation as a tree buried in a lake with only the tips of it's uppermost branches showing. We can only guess at the divisions below the water, or where the branches spring from.

Probably greater or lesser specialisation would be a better term. Some plants are more specialised for the niche they inhabit than others. This however has dangers for evolution because should conditions change the ultra specialist is least likely to survive, so called "highly evolved" can often be a path to extinction. Generally the "jack of all trades but master of none" is the most likely to survive if conditions change because they can more easily fit a variety of niches.

I always maintain Darwin got his emphasis wrong. Evolution works on eliminating only the terminally unfittest, leaving a range of species with greater or lesser suitability for their habitat, providing their variation is not terminal and allows them to breed. Survival of the fittest would mean there was by now only one ideal form left inhabiting every niche, which is patently untrue and would be disadvantageous for evolution if conditions changed.

DaveW

[Greenlarry]

The thing is evolution hasn't finished,its ongoing so altho there may be many different types of one organism in one environment eventually those less fitting to that situation may well eventally succumb.(survival of the fittest not meaning what today's society would think but rather those organisms that fit best into a particular environment)