Most young leaves pale in comparison to mature leaves: delayed greening is neither binary nor tropical

Delayed greening, the phenomenon in which expanding leaves appear red, blue or pale green due to low chlorophyll content, has long intrigued ecologists. However, little is known about what type of species are most likely to delay greening or which environmental conditions are associated with delayed greening. We spectroscopically quantified leaf pigments in 105 species from 12 representative terrestrial ecosystems, spanning from 16°S to 43°S, and assessed delayed greening as the log ratio of the average chlorophyll content in expanding and mature leaves. Contrary to the traditional binary view of delayed greening, we observed a normal distribution in the level of delayed greening species have, with expanding leaves containing, on average, half the chlorophyll of mature leaves. Surprisingly, there was no significant latitudinal gradient in the level of delayed greening. Herbivory showed no correlation with the level of delayed greening but a positive association with anthocyanin levels. Delayed greening levels tended to be lower in sites with near-neutral soil pH, greater in plant species with higher leaf surface and leaf mass per area, and exhibited no association with soil available nitrogen and organic carbon content. We suggest that a tradition of considering continuous variables in discrete categories can affect the way researchers think about a trait and potentially impede progress in understanding ecological strategy.