Perhaps no one other than a "shroomer" will ever notice or care, but departing cottonwood habitats take with them the Pleurotus ostreatus (plu-RO-tus = "layers"; os-tree-AYE-tus = "oyster"), or "oyster mushroom," which emerges from dead cottonwoods in spring and fall. It is edible and, as is known today, is medicinally useful in reducing cholesterol.
Mushrooms are mentioned by the journalists only once. On June 19, 1806, Pierre Cruzatte brought Captain Lewis several large morels – possibly black morels, Morchella angusticeps (mor-CHELL-a = "Moorish," ang-goo-STY-ceps = "narrow"), or sponge morels, Morchella esculenta (es-koo-LEN-ta ="edible"). Lewis roasted and ate them "without salt pepper or grease," and found them "truly an insippid taistless food." Fortunately for them, Cruzatte's knowledge of the morel was accurate, and he evidently knew better than to recommend any other species to his Corps mates.