 Differences between Hydnellum species tend to be more distinguishable in younger specimens . Fruitbody development is greatly influenced by environmental factors such as levels of rainfall , drying winds , and temperature . The blue tooth ( H. caeruleum ) , for example , develops a deeper blue color when it grows during cooler autumn weather . Optimal growth occurs during periods of frequent light rains and high humidity ; if the habitat dries out , growth will stop , but may resume after further precipitation . This intermittent growth affects the fruitbodies of different species to variable extents , leading to large variations in form , surface texture , and color . The morphological variability of fruitbodies and the dependence of their appearance upon environmental conditions has made Hydnellum a difficult group to study . Canadian mycologist Kenneth A. Harrison , who described several new species from North America , noted " [ t ] he remarkable longevity of individual sporophores of many species and the changes in appearance that occur during the long period of their development have confused all workers studying this group . " For example , H. aurantiacum , initially white , becomes in turn shades of orange , rusty @-@ brown , and brownish @-@ black . Its fruitbody initially has a turbinate ( cushion @-@ like ) shape with a lumpy surface , later becoming flattened to funnel @-@ shaped with a smooth to corrugated surface texture . 
