 Like many other mushrooms , L. indigo develops from a <unk> , or <unk> , that forms within the underground mycelium , a mass of threadlike fungal cells called hyphae that make up the bulk of the organism . Under appropriate environmental conditions of temperature , humidity , and nutrient availability , the visible reproductive structures ( fruit bodies ) are formed . The cap of the fruit body , measuring between 5 and 15 cm ( 2 @.@ 0 and 5 @.@ 9 in ) in diameter , is initially convex and later develops a central depression ; in age it becomes even more deeply depressed , becoming somewhat funnel @-@ shaped as the edge of the cap <unk> upward . The margin of the cap is rolled <unk> when young , but <unk> and <unk> as it matures . The cap surface is indigo blue when fresh , but fades to a paler <unk> or silvery @-@ blue , sometimes with greenish <unk> . It is often <unk> : marked with concentric lines that form alternating pale and darker zones , and the cap may have dark blue spots , especially towards the edge . Young caps are sticky to the touch . 
