I'd probably looked at hundreds of Bracken Ferns (Pteridium aquilinum) before a teacher drew my attention to what is now my favorite feature on this common fern. Where one of the side branches met the stalk on a young frond, there happened to be an ant. He explained that this fern has special organs called axillary nectaries that serve as a food source for ants and other insects. I later read that, in exchange for nectar, the ants spend time watching over the vulnerable growing plants and discourage (or kill) insect herbivores from nibbling on the unfurling frond. Once the fronds have fully expanded, the nectaries dry up and the ants look elsewhere for nourishment.