Leaf traits can tell us a lot about how plants work. Scientists studied different leaf traits to see how they relate to how plants control their stomata (tiny openings on leaves). They found that traits like leaf carbon concentration can predict how plants regulate their stomata in response to changes in humidity. Traits not included in the usual leaf trait framework also played a role, with species having more stomata being better at adjusting to humidity changes. Overall, traits related to stomata and veins were better at predicting stomatal regulation than traits commonly used in plant studies.