You’ve probably stepped on some quite recently. Or at least walked by, or even sat on a patch, though perhaps without registering what “they” were. Ordinary, near ubiquitous, seemingly static or at least glacially slow-growing, and not particularly cute or charismatic, lichen are seldom observed consciously at all, much less celebrated, related to, or clearly understood. Like a riddle straddling the edges of the living and the physical environment—faint dustings of powder or inert, wispy fronds—lichen occupies a subliminal place in most other creatures’ perceptions and consciousness. A. Laurie Palmer’s ongoing The Lichen Museum project, on which she has been working for more than a decade, resolves in a new book that endeavors to re-focus human attention as an act of aesthetic intervention—i.e., both conceptually as well as perceptually. A series of thematically oriented chapters (“Lichen Time,” “In Place,” and “More than One” among them) interleave excerpts from ecological texts and interviews with scientists with her own accounts of lichens and lichenology, and range from natural observation to philosophical abstraction. Reading this work thus feels like taking a series of walks with a particularly curious and sensitive companion, consistently attentive to otherwise neglected facets of the actual environment. Yet Palmer’s …