Three new species of Agaricus from Baiyun Mountain, Guangzhou, China

Agaricus is a species-rich genus with more than 600 species around the world. In this work, three new species, Agaricus cacainus, A. baiyunensis, and A. praeclarefibrillosus are described from the specimens collected at Baiyun Mountain, Guangzhou, China, a subtropical area with a monsoon maritime climate, based on phylogenetic analyses and morphological examinations of internal transcribed spacer (ITS1-5.8S-ITS2 = ITS), D1/D2 domains of the large subunit of ribosomal DNA (28S), and a part of translation elongation factor 1-alpha (TEF1). Agaricus cacainus in A. sect. Amoeni is characterized by a parabolic to applanate, slightly depressed pileus covered with chocolate brown, appressed, triangular squamules against white background, a white, furfuraceous stipe, an unchanging context when cut, a fragile and evanescent annulus, usually 4- or 2-spored basidia, and mostly pyriform cheilocystidia. Agaricus baiyunensis in A. sect. Minores has a pileus with a slightly truncate top covered with light brown, downy-wooly fibrillose scales and a light yellowish stipe with membranous annulus. Agaricus praeclarefibrillosus in A. sect. Brunneopicti is characterized by a pileus surface with brownish, triangular, recurved scales and longitudinally splitting lines toward margin, a cottony stipe with white, tiny, recurved fibrils, a single annulus, and variously shaped cheilocystidia, with sparsely ornamented basidiospores. The detailed comparison of their morphological characteristics with closely related species is provided.蘑菇属（Agaricus）是一个物种多样性丰富的类群，全球已知物种超600种。本研究以采集自中国广州白云山（属季风海洋性气候的亚热带区域）的标本为研究材料，基于对核糖体DNA内部转录间隔区（internal transcribed spacer，ITS1-5.8S-ITS2 = ITS）、核糖体大亚基D1/D2结构域（28S）以及翻译延伸因子1-α（translation elongation factor 1-alpha，TEF1）部分序列的系统发育分析与形态学检测，描述了3个新物种：Agaricus cacainus、A. baiyunensis及A. praeclarefibrillosus。其中隶属于蘑菇属优雅组（A. sect. Amoeni）的Agaricus cacainus，其菌盖呈抛物线形至平展状，略微凹陷，底色洁白，表面覆盖巧克力褐色、贴生的三角形鳞片；菌柄白色，具粉霜状质感；菌肉受伤后无变色反应；菌环脆弱且易消散；担子多为4孢或2孢；褶缘囊状体多呈梨形。隶属于蘑菇属小型组（A. sect. Minores）的Agaricus baiyunensis，其菌盖顶部稍平截，表面被浅褐色、绒毛状纤维鳞片覆盖；菌柄淡黄色，具膜质菌环。隶属于蘑菇属褐纹组（A. sect. Brunneopicti）的Agaricus praeclarefibrillosus，其菌盖表面具褐色、三角形反折鳞片，向边缘延伸有纵向开裂纹路；菌柄呈棉絮状，表面分布白色、微小的反折纤毛；具单个菌环；担子孢子纹饰稀疏，褶缘囊状体形状多样。本研究还详细对比了这三个新物种与近缘类群的形态学特征。