The veiled species of Hebeloma in the western United States / Alexander H. Smith, Vera Stucky Evenson, and Duane H. Mitchel.

Introduction

5

on the outwash areas. These are generally different from those found
on seepage areas under herbaceous vegetation on mountain slopes.
Seasonal variations of Hebeloma and Cortinarius fruitings are
also similar. Though not usually part of the "snow-bank" mushroom
flora of the Rocky Mountains, some veiled species of Hebeloma, e.g.,
H. mesophaeum, and some species of Cortinarius, e.g., C. ahsii, appear soon after the snow melts. The species found on stream banks
after the spring run-off are seldom the same as the ones found on
seepage areas in midsummer. July 15 to August 15 has been the major
fruiting period for the past eight years in central Colorado for both
Hebeloma and Cortinarius. Usually a week of rainy weather sometime
between these dates has triggered heavy fruiting of both genera. In the
Pacific Northwest both genera fruit heavily during the fall season:
September to October in the Cascades, and along the coast from October through November. Hebeloma species at times do fruit in almost
unbelievable numbers, as stated by Arora (1979). One can only speculate on the life pattern of the species that show this irregular fruiting
pattern. Years of experience collecting in the western area suggest that
these abundant fruitings are triggered by ideal conditions of moisture
and temperature and an unlimited and readily available food supply.
Exactly this same pattern of fruiting has been noted for years here in
North America for both genera. Some Cortinarii fruit every season
given merely adequate moisture and temperature. In about one year in
ten, however, tremendous fruitings of "rare" species appear along with
those known to fruit regularly. Sudden availability and/or quantity of
food seems to have little bearing on this fruiting behavior since Hebeloma species are mycorrhiza formers (Hacskaylo and Bruchet 1972).
As far as Hebeloma is concerned, species fruit from early spring
to late fall in protected plantings as well as in the forest. But over and
above all these considerations, one still encounters oddities in the fruiting pattern of the various species. For instance, during the entire summer of 1981 we were able to find hardly a half-dozen collections of
veiled Hebeloma species, whereas for the previous seven years we
collected more than that on almost every day in the field. We would
never have embarked on the present project if the 1981 season had
been our first.
One of the problems confronting the student of veiled Hebeloma
species is the problem of mixed collections. These fungi often fruit in a
scattered pattern in a restricted area, and the basidiocarps can all
closely resemble each other. It is not surprising then, that the toxicology of the genus is almost completely unknown. Given the usual starting point, a case of poisoning, where does one start to determine the
culprit? If an experienced taxonomist has difficulty avoiding mixed
collections, how can a reliable specimen of the offending mushroom be