Related to: 37 ways that words can be wrong.
Consider the following sentence (from Internet; but I have heard it before): 'Lichens consist of fungi and algae, but they are more than the sum of their constituents.'
It is supposed to say something like 'the fungus and the alga don't just live very close to each other, they influence each other's habitat(s) and can be considered, for most purposes, to form a physiologically integrated body'. It never actually says that, although people gradually come to this conclusion if they look at illustrations or read long enough. And I don't think the phrase is sufficiently catchy to explain its popularity; rather, that it is a tenuous introduction to the much-later-explained term 'synergism'. A noble (in principle) preparation of the mind.
Yet how is a lichen 'more than the sum of fungus and alga'? I suppose one could speak of a 'sum' if the lichen was pulverized and consumed as medicine, and then its effect on the patient was compared to that of the mixture of similarly treated fungus (grown how exactly?) and alga (same here). It doesn't exist in the wild. It shouldn't exist in the literature.
A child is not bothered by its lack of sense. When she encounters 'synergism', she'll remember having been told of something like it, and be reassured by the unity of science. It flies under the radar of 'established biological myths', because it doesn't have enough meaning to be one.
I picked a dictionary of zoological terms and tried to recall how the notions were put before me for the first time, but of course I failed. (I guess it should be high-level things, like 'variability', or colloquial expressions - 'bold as a lion', etc., that distort and get distorted the most.) They seem to 'have always been there'. Then, I looked at the definitions and tried to imagine them misapplied (intuitively, a simpler task). No luck. Yet someday, something other truly unknown to me will appear familiar and simple.
We can weed out improper concepts from textbooks, but there are too many sources which are written far more engagingly and 'clearly', and which propagate not even wrong ideas. Explained like I'm five.
And never named.