a) I think it is not that simple. The combination of fungus and algae is
given its
own taxonomic name, the lichen name. A lichen taxon always identifies at least two organisms.
It may be two "organisms", but its taxonomically homogeneous because it has one (lichen) taxon name. I didn't advocate that Organisms be "phylogenetically homogenous", only "taxonomically homogeneous". If Lichen names are intended to represent a taxon, then I still don't see the problem.
b) I think we very often use the main, dominant organism when recording mutualistic symbiosis. Most trees and many other plants die without their mycorrhiza. No group of oaks is taxonomically homogeneous - it is always a mixture of plant and fungus. We normally just know, but don't record this.
I
would like to be able to keep it that way. You can say definitions don't matter, I prefer to explicitly state the flexibility inside the def.
Perhaps, but maybe this is a perfect example of the difference between "Organism" and "CollectionObject"; the former should be taxonomically homogeneous, but the latter need not be.
That should not mean, that we should not record a symbiosis as two records where appropriate, just that there are good reasons not to force people to do it, because it would be at the expense of what they really want to achieve.
I don't think anyone is forcing anyone to do anything. If you want to talk about a fish as it swims through the water (or "sleeps" in a jar of alcohol), you create a single Organism instance for it, even though there are many symbionts physically attached to it. If/when you need to recognize these symbionts as individual things with their own properties (e.g., taxonomic identifications), you then create the necessary Organism instances to which those properties are applied.
Rich