The taxonomy regarding three closely related genera of Agaricaceae, viz. Heinemannomyces, Hymenagaricus and Xanthagaricus, is updated based on morphological and four-locus molecular phylogenetic evidence from collections gathered in South China. Thirteen species identified from 122 collections are described, including Heinemannomyces splendidissimus, eight new species of Xanthagaricus, viz. X. boluoshanensis, X. chamaeleontinus, X. guangzhouensis, X. heinemannii, X. minimus, X. phylononcaeruleus, X. retisporus and X. scauinus, and four known species of Xanthagaricus, viz. X. erinaceus, X. ianthinus, X. necopinatus and X. purpureosquamulosus. Among them, He. splendidissimus is phylogenetically recognized as a Hymenagaricus species, namely Hy. splendidissimus, and Xanthagaricus heinemannii is morphologically similar to Hy. splendidissimus in floccose squamules on the pileus and stipe. Both species have pileus squamules composed of inflated cells in the lower layer and hyphae forming an irregular trichoderm in the upper layer. However, X. heinemannii differs from Hy. splendidissimus by the context not turning reddish after damaged, brownish lamellae, and usually without hymeniform elements in pileus squamules. These findings suggest that species of both Hymenagaricus and Xanthagaricus may present hyphae forming an irregular trichoderm in pileus squamules. Xanthagaricus erinaceus is rediscovered after 40 years, together with X. necopinatus and X. purpureosquamulosus are three newly recorded species in China.