A maple leaf is more than it appears to be. Its substance is made not just from plant cells, but from a community of many species. “Maple” is in fact part plant, part fungus, part bacteria. Just as the human body is comprised of a vast “microbiome,” plants are also composite creatures.
To get a glimpse at this diversity, I cultured some of the fungal species found on and within the maple leaves growing on the tree by the front door.
To look at the fungi on the leaves’ surfaces, I dabbed maple leaves onto pertri dishes containing agar and fungus food, then waited a few days. Here is one such dish, displaying the diversity of species found on the leaf. Of course, many fungi don’t like petri dishes, so what we see below is a mere fraction of what is actually present on the leaf. The leaf itself is not so thickly coated; the petri dish gives fungi a place to grow and reveal themselves to our eyes.
These fungi from the surface are a mixed bag. Some are potentially harmful to the leaf and will ultimately eat the leaf away when it drops in the autumn. Others are likely protective or live as commensal squatters. Some feed on the droppings of caterpillars or the honeydew of aphids. A few might have drifted from the humans, goats, and stacked firewood below.
To peek at fungi that live inside the leaf, “endophytes,” I sliced some leaves into tiny pieces, sterilized their surfaces, then placed them onto petri dishes. Compared to the leaf “prints” taken from the surface, it took a couple of days longer for these endophytic fungi to appear on the dishes, but they too showed quite a diversity of forms. Here are two examples:
To make sure that I was not simply growing fungi that were wafting in the air or present on my forceps, I also ran some “control” plates which yielded either nothing at all or a few white blobs.
How endophytic fungi interact with tree leaves is largely unknown. But one of their roles is protective, secreting substances that deter the growth of pathogenic fungi. For example, endophytes isolated from Douglas maple release a chemical that poisons a variety of nasty plant diseases.
Interestingly, endophytes in sugar maple leavs seem to be more diverse in old growth forests than they are in younger, managed forests, or in urban areas. But these are preliminary findings. We have only the haziest understanding of the ecology of the fungal world hidden within leaf laminae.
Inside each leaf: a whole community. Within the community: hundreds of stories waiting to be heard. One story is clear, though: if we believe that creatures — humans included — live apart from “the other,” we’re deluded.