The study of organisms of the fungal lineage, including mushrooms, boletes, bracket or shelf fungi, powdery mildew, bread molds, yeasts, puffballs, morels, stinkhorns, truffles, smuts, and rusts. Fungi, in the traditional sense, are an ecological grouping of organisms found in every ecological niche. Mycologists estimate that there are 1.5 million species of fungi, with only 70,000 species now described. Fungi typically have a filamentous-branched somatic structure surrounded by thick cell walls; these structures are known as hyphae.