As always, your posts are enjoyable and most informative. Just a question: Is parallel evolution the same? Thats what I ve always described the relationship between Paphiopedium orchids from Asia and Phragmipedium from South America. Thanks

Thanks, Howard. I do have a jade picture around here somewhere to go along with the appreciation.

Yes, I think those two phrases are synonymous, related but equal, at least in my mind. No doubt an academic would say they're related but different ideas, as one parses out the differences between 'parallel' and 'convergent', and they'd be right, I'm reckoning.

Two different plant groups that adapted to the same environment. No doubt you heard 'Nature abhors a vacuum'. Where there's a empty space, nature tries to fill it.

As with so much of taxonomy, whether or not there are differences between the two is debatable. There are some who hold to considering the two terms as separate/distinct and others who believe they are one and the same. (Members of the latter group generally advocate dropping one of these terms from usage.)

Supporters of their usage essentially view the matter this way:

In both convergent and parallel evolution, similar environmental pressures can led to similar morphologies amongst diverse organism living in those conditions. Parallel evolution is when this occurs with unrelated organisms or organisms that are so distantly related they can be considered "unrelated." (An example would be the Gymnosperms (conifers and their close kin) and Angiosperms (flowering plants).) Convergent evolution is when this event occurs amongst related organisms. Just how far back one has to go for the evolutionary distance between two groups leads them to be considered "unrelated" I have no clue.

There is a short article here >>> article.

If one reads the section on homology and homoplasy, one will find the author's take on cacti and Euphorbia.

I used to think some of my Euphorbias were cactus, but I found out here that they are not. If they cannot be hybridized with cactus, then I think that they should remain separate (but equal!).

Any plant or animal that interbreeds and produce fertile offspring are of the same species. Like aloes, haworthia can produce fertile hybrids. I think most or all euphorbia can hybridize and produce hybrids. Not sure of this.