Ìrúgbìn igi óákù je nut of the oaks and their close relatives (genera Quercus and Lithocarpus, in the family Fagaceae). It usually contains a single seed (rarely two seeds), enclosed in a tough, leathery shell, and borne in a cup-shaped cupule. Acorns vary from 1–6 cm long and 0.8–4 cm broad. Acorns take between about 6 and 24 months (depending on the species) to mature; see List of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors. Nupa Acorn Soup (Miwokan recipe) Cooking With Acorns: A Major North American Indian Food Krautwurst, Terry (1988). "A Fall Field Guide Nuts". Mother Earth News. Retrieved 20 October 2009.  Unknown parameter |month= ignored (help) Julia F. Parker and Beverly R. Ortiz, It Will Live Forever: Traditional Yosemite Indian Acorn Preparation, Heyday Books, 2nd revised edition (1 September 1996), trade paperback, 160 pages, Àdàkọ:ISBN-10, Àdàkọ:ISBN-13 Proceedings of the symposium on the ecology, management, and utilization of California oaks, 26–28 June] USDA Forest Service General Technical Report PSW-044, Berkeley, California, 1980, edited by Timothy R. Plumb, 368 pages The symposium, held at Scripps College in Southern California, addressed most aspects of California's vast oak resource.