I'm somewhat irritated that "plants get their biomass through photosynthesis" is considered to be this field-specific botany knowledge. Not only because "sourced from x = made of x" is incredibly flimsy logic, but because it fails to follow that flimsy logic to the entertaining conclusion. Plants are the main primary producers in any food chain (and where it's not plants, it's photosynthetic algae or the like), so any carbon atom we eat was in a plant far more recently than it was in the air. That is, if "trees are made of air", then "ALL higher life is made of air".
Anyway, some more botanist internal monologues from me:
"I can't get over the fact that the roots and leaves of some trees are so genetically distinct they may as well be separate individuals." https://www.nature.com/news/tree-s-leaves-genetically-different-from-its-roots-1.11156
"I can't get over the fact that the oldest known organism is a clonal aspen colony that's 80 million years old" https://en.wikipedia.org/wiki/Pando_(tree)
"I can't believe plants independently developed the same broad-scale mechanism for innate immunity and non-self-recognition as animals did" https://en.wikipedia.org/wiki/Pathogen-associated_molecular_pattern
"I can't believe the parasite causing malaria probably used to be a peaceful photosynthetic creature at some point" https://en.wikipedia.org/wiki/Apicoplast
(Is the last one botany knowledge? The lines get really blurred once you delve into the evolutionary origin of plants and other photosynthetic organisms.)