Lepiotaceous fungi in California, U.S.A. Leucoagaricus sect. Piloselli

Eighteen red-bruising taxa in the Leucoagaricus/Leucocoprinus clade (Agaricaceae) are listed for California. Thirteen taxa are described in detail, with 7 proposed as new and 2 single specimen collections remaining unnamed. The species, all of which turn green with ammonia and produce spores without a germ pore, fall into 2 morphological groups (not phylogenetically supported): the pileus of one group comprises a trichodermal covering and the pileus surface of the second bears strands of repent, coloured hyphae. New taxa in the latter group are La. flammeotinctoides (more robust than Lepiota flammeotincta and with clavate cheilocystidia), La. pyrrhophaeus with irregular cheilocystidia and copper colours in the dried basidiocarps, and La. pyrrhulus with amygdaliform spores. Taxa in the 'trichodermal' group — L. fuliginescens, La. cupresseus, and La. erythrophaeus as well as new species La. adelphicus, La. pardalotus, La. hesperius, and La. dyscritus — are differentiated based on pileus covering, cheilocystidia, and reactions of the lamellae when damaged. The type collections of L. fuliginescens and L. flammeotincta were studied. DNA sequence data for all species are given and a key to 19 taxa, including La. georginae (from Washington), is provided.