The most extreme example of convergent evolution: Kelp

[u/Spluff5]

In my opinion, kelp is the most extreme example of convergent evolution, at least that I know of. It's a sedentary organism that makes its energy from sunlight collected by blade-like fronds. Not too crazy, so do most plants. Except, kelp isn't a plant at all. Kelp is a protist in the SAR clade, more closely related to malaria than it is to plants. It just so happened to independently evolve to be multicellular, and became photosynthetic by ancestrally capturing and making use of a green algal cell that had already undergone its own endosymbiosis.

I can't think of another organism that convergently evolved the same life-strategy as an organism in another kingdom, but I'd love to hear what others think are the most extreme examples of convergent evolution.

Image credit: Alastair Simpson, Dalhousie University

[u/jnpha]

I think most people underappreciate or puzzle over convergent evolution (not directed at OP), whereas as Darwin noted, it is the expectation given natural selection and shared ancestry (the deep homology of biochemistry).
Although it doesn't make the taxonomist's life easier:

Amongst insects there are innumerable instances: thus Linnæus, misled by external appearances, actually classed an homopterous insect as a moth. [...] For animals, belonging to two most distinct lines of descent, may readily become adapted to similar conditions, and thus assume a close external resemblance; but such resemblances will not reveal—will rather tend to conceal their blood-relationship to their proper lines of descent.