Xanthagaricus flavosquamosus and X. necopinatus, two new species of Agaricaceae, are described and illustrated from Asia. Macroscopically, both species are closely related to each other, but there are obvious micromorphological and molecular differences between them. Morphological and phylogenetic data showed that the two new species are distinct from other known species of the genus Xanthagaricus. Xanthagaricus flavosquamosus from China is characterized by its small, yellow basidiomata, short clavate cheilocystidia, epithelial pileipellis, and verrucose basidiospores measuring 5–5.5 × 3–3.5 μm. Xanthagaricus necopinatus from Bangladesh is characterized by having small, yellow basidiomata, a fugacious annulus, clavate to narrowly clavate cheilocystidia, epithelial pileipellis, and rugulose-rough basidiospores measuring 4–5 × 2.7–3.2 μm. In addition to the new species, a Heinemannomyces collection from China is reported. Morphological data and molecular phylogenetic analyses fully support the Chinese collection being Heinemannomyces splendidissimus, a species of Agaricaceae, originally described from Southeast Asia. Detailed descriptions, color photos and illustrations of the three species are presented. A key to the genus Xanthagaricus occurring in Bangladesh and China is provided.

Hymenagaricus , molecular phylogeny, monophyly, South Asia, taxonomy

Xanthagaricus (Heinem.) Little Flower, Hosag. & T.K. Abraham is mainly characterized by small basidiomata with squamulose pileus, epithelial pileipellis, and more or less yellow-colored basidiospores (Little Flower et al. 1997; Hosen et al. 2017). This genus was originally placed in Hymenagaricus Heinem. subgenus Xanthagaricus Heinem. by Heinemann and Little Flower (1984) with the type species X. flavidorufus (Berk. & Broome) Heinem. & Little Flower. Heinemann (1981) erected Hymenagaricus as an independent genus in the family Agaricaceae with the type species H. hymenopileus (Heinem.) Heinem., and is characterized by a squamulose pileus, a hymeniform pileipellis, and brown basidiospores (Heinemann and Little Flower 1984, Ge et al. 2008, Hosen et a. 2017). The epithelial pileipellis and yellow basidiospores of the subgenus Xanthagaricus did not fit completely with the genus circumscription of Hymenagaricus. Subsequently, the subgenus Xanthagaricus was elevated to the genus level in Agaricaceae (Little Flower et al. 1997).

Species in the genus Xanthagaricus are saprotrophic, and mainly distributed in Asia and South Africa. For instance, 11 species from India (Heinemann and Little Flower 1984, Little Flower et al. 1997), four species from Sri Lanka (Heinemann and Little Flower 1984, Pegler 1986, Little Flower et al. 1997), two species from Africa (Reid and Eicker 1995, 1998), one species each from mainland China (Hosen et al. 2017), Pakistan (Hussain et al. 2017), and Taiwan, China (Ge et al. 2008) have so far been validly reported. However, Asia has more than the currently known species of Xanthagaricus, as sequences of several species of this genus are available in GenBank, especially from Thailand and Malaysia. Index Fungorum (http://www.indexfungorum.org/Names/Names.asp) lists 12 taxa of Xanthagaricus. However, a recent study by Hussain et al. (2017) has transferred six species to Xanthagaricus from Hymenagaricus.

Watling (1998) circumscribed Heinemannomyces as an independent monotypic genus in the family Agaricaceae from specimens collected in Malaysia and Thailand. Since then, no additional species with detailed descriptions and geographical extensions of the genus Heinemannomyces have been reported so far. Heinemannomyces is distinguished by its medium-sized basidiomata, extremely woolly-arachnoid veils on the pileus surface composed of cylindrical cells, leaden gray to dark blue lamellae, and reddening context when injured (Watling 1998). Phylogenetically, Heinemannomyces is closely related to Hymenagaricus, but can be differentiated by its morphology.

In this study, three collections of Xanthagaricus and Heinemannomyces from China, and one collection of Xanthagaricus with several basidiomata from tropical Bangladesh were examined. Based on macromorphology, both East Asian and South Asian Xanthagaricus collections could be the same species. However, careful microscopic observations along with molecular data revealed that they are not conspecific, but represent undescribed species within Xanthagaricus. In addition, a brief description from the Chinese collection of Heinemannomyces is provided along with molecular data. With the inclusion of the two new species of Xanthagaricus in this study and another two recently described new species, namely X. caeruleus Iqbal Hosen, T.H. Li & Z.P. Song (Hosen et al. 2017) and X. pakistanicus Hussain, Afshan & Ahmed (Hussain et al. 2017), the number of known species of this genus increases to 22.

Little Flower et al. (1997) defined Xanthagaricus to include taxa with “basidiomata small, pileus with characteristic woolly squamules and appendiculate margin; lamellae free, brown when mature; stipe cylindrical, slender, fistulose, slightly broader at the apex, veil absent; context thin, sometimes becoming vinaceous red on bruising; spore print brown, spores subglobose to ellipsoid, smooth, thick-walled, brown with yellowish tinge; lamellar edge heteromorphous; cheilocystidia present; hymenophoral trama regular to subregular; pileal surface a disrupted epicutis of radial hyphae with plenty of spherical or subspherical cells at the scales; clamp connections absent”. In spite of that, some species of Xanthagaricus do not warrant the generic circumscription on account of lamellae color (ink-blue in X. caeruleus), presence of an annulus (tiny and fugacious annulus in X. necopinatus), basidiospore color (greenish gray to grayish brown in X. caeruleus) with either smooth (X. caeruleus) or ornamented basidiospores (X. flavosquamosus, X. necopinatus, X. epipastus, X. subepipastus, etc.), but share the common features like small basidiomata, squamulose pileus, epithelial pileipellis with globose to subglobose terminal elements, the presence of cheilocystidia, the absence of pleurocystidia, more or less yellow to brownish yellow basidiospores, and the absence of clamp connections. It should be noted that most species of the genus Xanthagaricus have ornamented basidiospores (figs 15c–h, 16 in Little Flower et al. 1997) but it was not mentioned in the genus circumscription by the authors (1997).

Macromorphologically, both new species are superficially close to each other, and could be confused in the field, although X. flavosquamosus has relatively larger squamules, no annulus and slightly lighter color that X. necopinatus. However, they can be separated microscopically. Xanthagaricus flavosquamosus has short and broadly clavate cheilocystidia, comparatively larger and wider basidiospores with a verrucose surface under SEM, while X. necopinatus has narrowly clavate cheilocystidia and shorter basidiospores with a rugulose-rough surface under SEM. Furthermore, these two species are in different clades in the phylogeny. Xanthagaricus flavosquamosus creates a new phyletic line with weak support, while X. necopinatus is a close relative to X. pakistanicus with strong BS support value (93% ML BS, Fig. 1). However, morphologically, X. pakistanicus has a light orange-yellow to moderate orange-yellow pileus, and globose to subglobose basidiospores measuring 7–7.5 × 6.5–7.0 µm (Hussain et al. 2017).

Some morphologically closely related species to be compared to X. necopinatus and X. flavosquamosus are X. epipastus, X. ochraceoluteus (D.A. Reid & Eicker) Hussain, X. subepipastus (Heinem. & Little Flower) Little Flower, Hosag. & T.K. Abraham, and X. viridulus (Heinem. & Little Flower) Little Flower, Hosag. & T.K. Abraham. The latter two species differ from X. necopinatus in having comparatively larger and wider basidiospores (Heinemann and Little Flower 1984, Daniëls et al. 2015). Xanthagaricus epipastus has an olive yellow to olivaceous squamulose pileus, and slightly wider basidiospores (3.7–4.7 × 2.8–3.4 µm) with lower Q value (avg. 1.36) (Heinemann and Little Flower 1984). Xanthagaricus ochraceoluteus differs from X. necopinatus in having olive-buff lamellae, no annulus, and variable cystidia. Xanthagaricus flavosquamosus has comparatively larger and wider basidiospores (5–5.5× 3–3.5 µm) than those of X. epipastus (see above), X. subepipastus (3.7–4.7 × 2.8–3.4) and X. viridulus (3.8–5.0 × 2.9–3.6 µm) (Heinemann and Little Flower 1984, Heinemann and Rammeloo 1986, Daniëls et al. 2015). Furthermore, X. epipastus has a pileus covered by olive yellow to olivaceous squamules (Heinemann and Little Flower 1984). Moreover, X. subepipastus and X. viridulus, originally described from the Kerala state of India, differ in having lageniform cheilocystidia (Heinemann and Little Flower 1984). Xanthagaricus viridulus also has an umbonate, brown, floccose-squamulose pileus, and lageniform to clavate cheilocystidia (Heinemann and Little Flower 1984). Xanthagaricus ochraceoluteus has olive-buff adnexed lamellae (Reid and Eicker 1998). Unfortunately, molecular data for the Indian collections and other comparable species are unavailable to include in this study.

Xanthagaricus taiwanensis (=Hymenagaricus taiwanensis Zhu L. Yang, Z.W. Ge & C.M. Chen), originally described from Taiwan, China is distinguished from X. flavosquamosus by having a yellow-brown pileus covered with fuscous brown-black squamules, a white membranous annulus, and comparatively wider basidiospores 5–5.5 × 3–4 µm (Ge et al. 2008). Xanthagaricus caeruleus, a recently described species from China, can also be distinguished from X. flavosquamosus by its grayish lilac to grayish violet squamules on pileus, ink-blue lamellae, and comparatively larger and smooth basidiospores 5–6 × 3–3.5 µm (Hosen et al. 2017). On the other hand, X. necopinatus is distinguished from all closely related species of this genus (see above), and the first contribution to the genus Xanthagaricus for Bangladesh.

It is interesting to note that Xanthagaricus appears to be a monophyletic genus and close sister to Pseudolepiota Z.W. Ge, a monotypic genus, recently described from China, with strong BS support value (85% ML BS). The latter genus is distinguished in having white color of the lamellae, hyaline basidiospores, and a subcutis pileipellis made up of slightly interwoven cylindrical hyphae (Ge and Yang 2017). However, the synapomorphic features of the two genera are the squamulose pileus, the absence of pleurocystidia, and the absence of clamp connections. Though a recent molecular study by Hosen et al. (2017) recovered Xanthagaricus as a close sister genus to Hymenagaricus, lacked significant BS support value while using ITS data. With the inclusion of eight species of Xanthagaricus including two new species based on ITS-28S phylogeny, the monophyly of the genus is resolved with the close evolutionary relationship to Pseudolepiota, and distinct from Hymenagaricus (Fig. 1).

The collection of Heinemannomyces made from south China matches well with the salient features (woolly-arachnoid veil on pileus, leaden gray lamellae, and a reddening context) of H. splendidissimus reported in the protologue by Watling (1998). However, the Chinese material slightly deviates from the original description in having comparatively larger basidiomata (up to 65 mm broad), and the absence of clamp connections. The authors were unable to include the type material of Heinemannomyces in the present study, but several sequences of H. splendidissimus from the type locality and its adjacent areas (Thailand) are available in the public accessible database (GenBank) to compare with the Chinese material. Sequences of Heinemannomyces from Thailand fall in the same clade with those from China, and are closely related to Hymenagaricus (Fig. 1). However, morphologically, Heinemannomyces differs from Hymenagaricus by having woolly-arachnoid veil remnants on the pileus surface, becoming brown, a reddening context when cut or injured, leaden gray lamellae, and a pileipellis composed of cylindrical hyphae (Watling 1998). It should be noted that three species of Hymenagaricus (GenBank voucher numbers. C.M. Chen 3636, T. Laessoe 6025 and ecv3807) used in this study (Xanthagaricus clade, Fig. 1) were also grouped together with strong BS support value in the molecular study of Vellinga et al. (2011) based on either ITS or multigene phylogeny, and Heinemannomyces was separated from them, and formed an independent lineage (Figs 2 and 3 in Vellinga et al. 2011). However, no additional species of Hymenagaricus from the Hymenagaricus-Heinemannomyces clade (Fig. 1) was included in the study of Vellinga et al. (2011). In the present analysis, more species of Hymenagaricus including some other close relative taxa of Agaricaceae were included, and Heinemannomyces showed a close affinity to Hymenagaricus (Fig. 1). One possible classification would be to collapse Heinemannomyces into a single genus Hymenagaricus or separate it into a subgenus/section. However, there are some remarkable morphological characteristics for Heinemannomyces and Hymenagaricus, which supports separating them into different genera. Further exploration of Hymenagaricus/Heinemannomyces species diversity and historical biogeography from Asia/South Africa, which seems to be species rich in these genera, could help to confirm or refute the hypothesis of monophyly/paraphyly of Hymenagaricus.

The authors are very grateful to Dr. David Ratkowsky (University of Tasmania, Australia) for checking the English in the manuscript. The first author thanks Shah Hussain (University of Swat, Pakistan) for providing invaluable information on Xanthagaricus pakistanicus prior to formal publication. Dr. Zai-Wei Ge (Kunming Institute of Botany, China) is acknowledged for providing sequences data of Pseudolepiota zangmui. Dr. Ming Zhang, Mr. Jun Ping Zhou and Mr. Hao Huang (Guangdong Institute of Microbiology, China) are acknowledged for providing voucher specimens. This work was supported by the NSFC Research Fund for International Young Scientists (No. 31750110476) and China Postdoctoral Science Foundation Grant (No. 2017M610514, 61^st Phase) to the first author. This study was also partially supported by the Science and Technology Program of Guangzhou, China (No. 201607020017), the National Natural Science Foundation of China (No. 31670029), and the Ministry of Science and Technology of China (Nos. 2013FY111500 and 2013FY111200).