Braiding Sweetgrass: Chapter 23 Summary & Analysis

Again in the Adirondacks, Robin explores a lakeside forest and examines a massive granite boulder that is entirely covered in lichens. These are Umbilicaria americana, also known as rock tripe or oakleaf lichen. The thallus, or body, of Umbilicaria is circular and brown, curled up at the edges to reveal a black underside like a “charred potato chip.” Lichens are not technically plants, Kimmerer explains, and in fact they also blur the line between individual and union, as they are a lifeform composed of a symbiosis between a fungus and an alga.

Kimmerer compares this partnership to a marriage, like her own parents who are about to celebrate their sixtieth anniversary. Their partnership not only benefits the two of them, but also those around them. This is the case with many lichens as well. In a Native American wedding, Kimmerer explains, the bride and groom bring gifts for each other to cement their union, and similarly the alga and the fungus bring gifts for each other in their lichen partnership.

The alga is able to make its own sugar through photosynthesis, but it lacks minerals and cannot keep itself from drying out. The fungus dissolves material into minerals that the alga can use, but it must feed off the sugar that the alga creates because it cannot make its own. In Umbilicaria, the fungi always choose the alga Trebouxia as their partner, while Trebouxia itself partners with other kinds of fungi as well—sort of like a marriage with one more promiscuous partner.

Kimmerer describes the layers of Umbilicaria’s thallus, which work to preserve moisture and distribute sugar and minerals. She notes that some researchers don’t see the fungus as a marriage, but as “reciprocal parasitism,” or “fungi who discovered agriculture” by ensnaring the algae and feeding off of their photosynthesis. There are some of these partnerships where the individual cannot survive without the other at all, however, and scientists are still studying why some species join together and others do not. Sometimes two species that would normally form a lichen in the wild will not do so in a lab—that is, until they are placed under conditions of scarcity. Then they turn to reciprocity to best survive.

Umbilicaria usually looks dry and dead, Kimmerer says, but really it is just waiting to be transformed by the rain, when it swells and turns green, forming dimples like a belly button. Robin examines the lichen on the boulder and thinks about how these ancient life forms are connected to the earth by an “umbilicus,” like their name and the belly buttons that they form. Just as the lichen is nourished by the stone it is attached to, so people can also derive nourishment from the lichen. It can be soaked, rinsed, and boiled to form a nutritious broth, with the thallus itself chopped into a pasta-like strips.

Sometimes when Umbilicaria grows too thick it starts to create soil around itself on which moss and ferns can grow, thus laying the foundation for new life when its own life flourishes. Robin observes a rock face covered in Umbilicaria which is also surrounded by various algae and mosses, some of them crowding out the lichen itself.

Lichens are some of the oldest life forms on earth, and in their very nature they embody the principle of reciprocity, Kimmerer says, giving and receiving within a single organism. In this they too are teachers about the power of mutualism. Yet while they can teach and nourish human beings, manmade pollution and climate change threaten these sensitive beings. Kimmerer feels sure that lichens will endure, but she is not so sure about humans. To close the chapter, she explains that in Asia Umbilicaria is known as the “ear of stone,” and she imagines it quietly listening to our growth and now our anguish. Perhaps someday it will hear our joy as well, if we too are able to “marry ourselves to the earth.”