The thing with lay definitions is that they are rarely rigidly fixed, and the nuance in meaning is often directly suggested by context. If I say something like, “I took a bunch of photos of plants in the woods, here are some pictures” and there were mushrooms among the pictures, it would not be reasonable to raise an objection to the use of “plants” in this case. But if someone said “I’m setting up my specimen garden, and I’m growing six new plants and four new fungi” then the exclusion of fungi from this use of plant is contextually obvious. Both of these are informal uses (as presented), and both are correct.
(There are also technical examples of this: when a herpetologist says “turtles” do they mean to exclude tortoises, or are they referring to all chelonians? It depends. (Also, what does a soil scientist mean when they say “sand”?))
Hoo boy.
