A keystone species is an organism that defines and supports an entire ecosystem, filling a vital ecological niche. Without these species, the ecosystem would be radically altered or even collapse. This pocket-sized field guide by bestselling naturalist Collin Varner highlights 50 keystone trees, flowering plants, fruit-bearing plants, marine plants, and fungi found across the Pacific Northwest bioregion—including Douglas Fir, Sitka Spruce, Large-leafed Lupine, Wild Mint, Salal, Salmonberry, Marine Eelgrass, Red-belted Polypore, and more. Each entry features clear photography, etymology, descriptions, habitat information, risks and warnings. This convenient and easy reference is perfect for casual walkers, hikers, campers, and beachcombers, and draws awareness to the importance of conservation and protection of these crucial species.