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Chapter 1 Introduction The Boletaceae Chevall.�� which belongs to the Boletales (Agaricomycetes) in Basidiomycota�� is a family that comprises species of fungi that produce a fleshy fruit body with tubular (or sometimes lamellar)hymenophore. In this book�� we adopt the family concept as defined by Binder and Hibbett (2006)�� i.e.�� the fruit body is fleshy�� the hymenophore is tubular or lamellate�� the tube trama is often gelatinous�� and the spore prints are mostly vinaceous to reddish brown. As the color and texture of this kind of fungi are supposedly similar to those of the livers of cattle�� boletes are known as ��Niuganjun�� (cow liver) in China (Lan 1436). There are nearly 1000 species from about 80 genera described from this family worldwide�� and all of them have great ecological value�� and many are also economically important. 1.1 Ecological and economic values of boletes The family Boletaceae is both ecologically and economically important. Most of the species are ectomycorrhizal symbionts of woody plants�� with more than ten families of plants (including Betulaceae�� Dipterocarpaceae�� Fagaceae�� Pinaceae�� Salicaceae) known to form mycorrhizal relationships with boletes. These fungi play vital roles in maintaining forest ecosystems�� vegetation restoration�� and water and soil protection (van der Heijden et al. 1998; Kernaghan 2005; Rinaldi et al. 2008; Eastwood et al. 2011). The symbiotic ectomycorrhizal relationships are thought to contribute to the diversification of both fungi and their host plants (Wang and Qiu 2006)�� and it is thought to be this mycorrhizal association that strongly drives evolution and leads to the richness of genera and species�� the diverse morphology�� the complicated microscopic structure�� the wide ecological distribution�� and the presence of both convergent and parallel evolution in the Boletaceae (Singer 1986; Bruns et al. 1989; Binder and Bresinsky 2002a; Binder and Hibbett 2006; Nuhn et al. 2013; Wu et al. 2014�� 2016a). Many species in the Boletaceae are very important worldwide as delicacies�� including the species of the Boletus edulis complex�� which are famous across the world markets as porcini mushrooms (Dentinger et al. 2010)�� and are considered among the best of the edible fungi. During the Chinese mushroom season�� it is usual to see people searching in forests for the ��Huang Niugan�� (Tylopilus pseudoballoui D. Chakr.�� K. Das & Vizzini) or ��Bai Cong�� [Butyriboletus roseoflavus (M. Zang and H.B. Li) D. Arora and J.L. Frank] (Yang et al. 2021). Some species are also used in herbal medicines�� or have bioactive metabolites (Heleno et al. 2011)�� while other species are toxic�� and perhaps even lethally so (Benjamin 1995; Matsuura et al. 2007). However�� due to excessive long-term over-collection�� habitat damage�� and global warming�� some species or populations are probably in danger of extinction. The study of boletes is therefore crucial for their conservation�� utilization�� and to prevent poisoning. 1.2 Historical research in the Boletaceae The type genus of the Boletaceae is Boletus L. The name Boletus was first applied to the fleshy�� stipitate�� poroid fungi by Dillenius in 1719 (Dillenius 1719). Linnaeus (1753) included all poroid fungi (boletes and polypores) under Boletus�� but Fries (1821) accepted Dillenius�� generic concept and created infrageneric taxa within Boletus based on the presence or absence of a veil and color of the hymenium and spore print. Since the establishment of Boletus�� a large number of taxonomic studies on the genus have been carried out worldwide�� and a great deal of research has been published (e.g.�� Peck 1873�� 1887; Snell and Dick 1941; Heinemann 1951; Hongo 1963�� 1968�� 1974a�� 1974b�� 1984a��1984b�� 1985; Snell and Dick 1970; Watling 1970; Smith and Thiers 1971; Corner 1972; Hongo and Nagasawa 1976; Wolfe 1979a�� 1979b; Singer 1986; Binder and Bresinsky 2002a�� 2002b; Nagasawa 1997; Li and Watling 1999; Watling and Li 1999; Bessette et al. 2000; Li et al. 2002; den Bakker and Noordeloos 2005; Zang 2006; Desjardin et al. 2008�� 2009; Nelson 2010; Horak 2011; Neves et al. 2012). However�� most of these studies focused on morphology�� subcellular structure�� and ecology. Species in the family Boletaceae are diverse in morphology�� complicated in structure�� and have wide ecological distribution. Some boletes are quite distinctive and easy to recognize�� while others can be exceedingly difficult to identify due to either parallel or convergent evolution�� even for experienced boletologists. Consequently�� it is hard to understand the systematics and evolution of boletes effectively through a single morphological approach. This may be the reason why Boletaceae is regarded as a taxonomically difficult family. Even E.M. Fries�� well-known as the ��Linnaeus of fungal taxonomy�� once said�� ��Nullum genus quam Boletorum magnis me molestavit (no genus has given me more trouble than that of the boleti)�� (Bessette et al. 2000). The a