Two taxonomically controversial polypore genera with reddish brown to orange basidiomata that stain reddish with KOH solution, Aurantiporus and Hapalopilus, are revised based on additional sampling, morphological examination, and phylogenetic analysis of a combined dataset of ITS1-5.8S-ITS2-nLSU sequences. Hapalopilus is a monophyletic genus belonging to Phanerochaetaceae, whereas Aurantiporus is a polyphyletic genus belonging to Meruliaceae. Hapalopilus and Aurantiporus s. str. are circumscribed, and two new species – Aurantiporus orientalis and Hapalopilus tabuliformis – are described and illustrated from temperate China. In addition, four new combinations, viz. Aurantiporus alboaurantius, A. mutans, A. tropicus and Luteoporia albocitrina, are proposed based on morphology and phylogenetic analysis. The relationships between Aurantiporus and Hapalopilus are discussed.

Phlebioid clade, phylogeny, taxonomy, wood-rotting fungi

Polypores are important wood-decaying fungi and have distribution in all the forest ecosystems; around 2670 polypores have been reported worldwide and some have economic values (Papp and Dai 2022; Wu et al. 2019, 2022; Yuan et al. 2023; Zhao et al. 2024). Aurantiporus Murrill and Hapalopilus P. Karst. are polypore genera with limited species producing reddish brown to orange basidiomata and belonging to the phlebioid clade of Polyporales (Chen et al. 2021). Aurantiporus was treated as a synonym of Hapalopilus by Ryvarden (1991), and its type species was accepted as Hapalopilus croceus (Pers.) Donk (Donk 1933). Until now, the name of Hapalopilus croceus is still accepted by some mycologists (Langer et al. 2015; Ryvarden and Melo 2017; Redr et al. 2020).

Aurantiporus was typified as Polyporus pilotae Schwein. (Murrill 1905) and is characterized by annual, bright-colored basidiomata staining more or less red with KOH solution, a monomitic hyphal system with agglutinated clamped hyphae, and hyaline, smooth, ellipsoid basidiospores which are negative in Cotton Blue (Niemelä et al. 2012; Rivoire 2020). Jahn (1974) pointed out that Hapalopilus croceus with different pigmentation and denser basidiomata consistency should be addressed in Aurantiporus. Moreover, recent phylogenetic studies showed that H. croceus was nested in the Meruliaceae clade and was distantly related to the type of Hapalopilus belonging to Phanerochaetaceae (Dvořák et al. 2014; Koszka and Papp 2020).

The genus Hapalopilus was established by Karsten (1881) and typified by Polyporus nidulans Fr. (= Hapalopilus rutilans (Pers.) Murrill 1904). Morphologically, the genus is known by its distinctive annual, colorful, soft basidiomata with a reddish to violet coloration upon contact with KOH solution, a monomitic hyphal system, generative hyphae bearing clamp connections, and hyaline, thin-walled, smooth basidiospores which are negative in Melzer’s reagent and Cotton Blue (Miettinen et al. 2016; Ryvarden and Melo 2017; Chen et al. 2021). The color change in KOH solution has been attributed to the presence of polyporic acid in H. rutilans, which renders the fungus poisonous (Kraft et al. 1998; Villa et al. 2013).

Previously, most polypore species with reddish KOH reaction were placed in Hapalopilus on a morphological basis (Gilbertson and Ryvarden 1986; Zmitrovich et al. 2006; Ryvarden and Melo 2017) and therefore Hapalopilus was considered polyphyletic in early molecular studies (Ko et al. 2001). Niemelä et al. (2005) established Erastia Niemelä & Kinnunen to accommodate H. salmonicolor (Berk. & M.A. Curtis) Pouzar, and recently two additional species, H. aurantiacus (Rostk.) Bondartsev & Singer and H. ochraceolateritius (Bondartsev) Bondartsev & Singer, were combined into this genus (Zmitrovich 2018; Zíbarová et al. 2021). Furthermore, the phylogenetic studies demonstrated that H. ochraceolateritius belonged to Irpicaceae (Justo et al. 2017; Chen et al. 2021; Li et al. 2022). However, the phylogenetic position of Erastia and its type species was uncertain. Based on molecular and morphological analyses, Miettinen et al. (2016) redefined Hapalopilus as monophyletic with a narrow concept that included its type species and three additional species within Phanerochaetaceae. Although this revised classification enhanced the clarity of phylogenetic relationships within Hapalopilus in Phanerochaetaceae, other species initially described in Hapalopilus were found in different clades of Polyporales, highlighting unresolved taxonomic issues (Ko et al. 2001; Justo et al. 2017; Chen et al. 2021).

To better understand the morphological variation and phylogeny of the above bright-colored polypores with basidiomata staining red in KOH solution, and especially the uncertain phylogenetic position of some species in Aurantiporus and Hapalopilus, we examined specimens from Asia and North America. Based on morphology and new molecular data, we provide an updated phylogeny of Aurantiporus and Hapalopilus. As a result, two new species are described and four new combinations are proposed in this study.

Despite the controversial history of Aurantiporus and Hapalopilus, there is certainty in the placement of the new species Aurantiporus orientalis and Hapalopilus tabuliformis. This placement is consistent with the type species of their corresponding genera (Fig. 1). Both species are found in the temperate forests of China and show bright-colored basidiomata with a reddish coloration in KOH solution.

Our phylogenetic analysis (Fig. 1) corroborates that Erastia and Hapalopilus are monophyletic and nested in different clades of Polyporales. Erastia was established to accommodate Hapalopilus species growing on coniferous wood (Niemelä et al. 2005), and it is nested in Irpicaceae including its type and two additional species in our phylogeny (Fig. 1.). Conversely, Hapalopilus is nested in Phanerochaetaceae as monophyletic clade which is in accordance with Miettinen et al. (2016), and includes five species here. In conclusion, Erastia and Hapalopilus are independent genera within Irpicaceae and Phanerochaetaceae, respectively.

Hapalopilus tabuliformis is an independent lineage within Hapalopilus, as indicated by the phylogenetic analysis of the combined ITS1-5.8S-ITS2-nLSU dataset (Fig. 1). Morphologically, H. eupatorii (P. Karst.) Spirin & Miettinen resembles H. tabuliformis by having resupinate to effused-reflexed basidiomata, fimbriate margin and similar sized ellipsoid basidiospores, but differs from H. tabuliformis by shorter basidia (14–18 µm vs. 18–31 μm) and longer basidiospores (3.4–4.5 µm vs. 3.2–4 µm; Miettinen et al. 2016; Zíbarová et al. 2021). Hapalopilus rutilans and H. ribicola (P. Karst.) Spirin & Miettinen differ from H. tabuliformis by basidiospore sizes (4–5 × 2.3–3 µm in H. ribicola and 3.2–5.1 × 2–2.7 µm in H. rutilans vs. 3.2–4 × 2.6–3.2 μm in H. tabuliformis) and shorter basidia (16.5–20.5 × 4.5–6 µm in H. ribicola and 18–22 × 5–6.5 µm in H. rutilans vs. 18–31 × 3.2–5.8 μm in H. tabuliformis; Miettinen et al. 2016; Ryvarden and Melo 2017). Moreover, the former two species have a wide distribution in Europe and commonly grow on deciduous trees (Miettinen et al. 2016), while H. tabuliformis is known from China and grow on Pinus. Hapalopilus percoctus differs from H. tabuliformis by having pileate basidiomata, longer basidiospores (3.8–4.6 µm vs. 3.2–4 µm), and is known to grow on dicots in the Southern Hemisphere (Miettinen et al. 2016).

Aurantiporus is found to be highly polyphyletic in the family Meruliaceae, as shown in our phylogenetic analysis as well as in previous studies (Floudas and Hibbett 2015; Chen et al. 2021; Liu et al. 2022). The type species of Aurantiporus was erected by Murrill (1905) as Polyporus pilotae Schwein. (Schweinitz 1832) described from North America, and was later considered by himself as a synonym of Polyporus croceus (Pers.) Fr. (=Boletus croceus Pers.; Persoon 1796; Fries 1815). Nevertheless, it is noteworthy that the sequences sampled from North America and Europe, and named as Hapalopilus croceus in GenBank, represent a species complex (Fig. 1). We do not doubt that Aurantiporus croceus or A. pilotae (Schwein.) Murrill belong to Aurantiporus rather than Hapalopilus. In addition, similar uncertainty exists within Aurantiporus priscus, which was synonymized as A. pseudoplacentus by Vampola and Vlasák (2021). Our phylogenetic analysis illustrated that they make form two closely related separate subclades (Fig. 1). However, Aurantiporus priscus in our phylogeny is represented by specimens from China and Russia Far East, with no sequences available from the type locality (Poland). So, further study is needed, especially the sequences from type locality are very important to confirm the species complex.

The new species Aurantiporus orientalis nested in the Aurantiporus s. str. clade (Fig. 1) and grouped together with the generic type (A. pilotae from North America, Fig. 1). Morphologically, these species share pileate, bright orange-red colored basidiomata and grow on Quercus. However, the generic type (A. pilotae from North America) differs from A. orientalis by the absence of cystidioles (Murrill 1905; Koszka and Papp 2020). Aurantiporus pseudoplacentus, A. mutans, and A. tropicus are similar to A. orientalis in having orangish basidiomata and similar shape and size of basidiospores, but A. pseudoplacentus, A. mutans, and A. tropicus differ from A. orientalis by the absence of cystidioles (Lowe 1966; Gilbertson and Ryvarden 1986; Lindblad and Ryvarden 1999; Vlasák et al. 2012). In addition, A. alboaurantius, A. roseus, and A. orientalis share a monomitic hyphal system with ellipsoid, thin-walled basidiospores and the presence of cystidioles (Cui and Zhao 2014; Zhao et al. 2015). However, A. alboaurantius and A. roseus differ from A. orientalis in having resupinate basidiomata and bigger basidiospores (4–5 × 3–3.3 µm in A. alboaurantius and 4–5.2 × 3.3–3.8 µm in A. roseus vs. 3.4–4 × 2.5–3 µm in A. orientalis; Cui and Zhao 2014; Zhao et al. 2015).

From a morphological perspective, Hapalopilus is characterized by pileate to resupinate, colorful, and soft to cottony corky basidiomata when fresh, brittle when dry, a monomitic hyphal system with generative hyphae bearing clamp connections, and covered with granular, golden yellow pigment that dissolves in KOH solution (Miettinen et al. 2016). Aurantiporus s. str. differs from Hapalopilus by having larger, watery and fleshy basidiomata when fresh, slower drying process, often shrinking significantly in size, denser agglutinated tubes, darker and hard when dried, generative hyphae somewhat colored, and usually covered with oily matter not dissolving in KOH solution (Jahn 1974; Zmitrovich et al. 2006; Wu et al. 2010; Niemelä et al. 2012; Vlasák et al. 2012). Moreover, the traditional concept of Aurantiporus has caused difficulty in defining certain species, such as A. pulcherrimus (Rodway) P.K. Buchanan & Hood, A. fissilis (Berk. & M.A. Curtis) H. Jahn, and A. alborubescens (Romell) H. Jahn, which were also combined into the genus Tyromyces P. Karst. due to morphological similarities (Reid 1967; Yao et al. 1999; Buchanan and Ryvarden 2000; Ryvarden and Melo 2017). These species seem to be phylogenetically distant from the type species of Aurantiporus, Hapalopilus, and Tyromyces (Binder et al. 2013; Floudas and Hibbett 2015; Liu et al. 2023). Recently, the genus Odoria V. Papp & Dima was established to accommodate A. alborubescens (Papp and Dima 2017), and Pappia Zmitr. was established for A. fissilis (Zmitrovich 2018), while the phylogenetic affiliations of other Aurantiporus species remained unclear. Our current phylogeny strongly supports the treatment of A. fissilis in the monophyletic genus Pappia. Additionally, the distinctive characteristics of whitish pileate basidiomata, shrinking significantly in size when dry, a pleasant and sweet smell, and the presence of chlamydospores, differentiate Pappia fissilis as a unique entity in both Aurantiporus and Tyromyces (Ryvarden and Melo 2017; Chen et al. 2021).

The genus Aurantiopileus D.L. Lindner & T.J. Baroni, typified as A. mayaensis Ginns, was erected by Ginns et al. (2010), and unlike Aurantiporus, it has cystidia. Confusingly, Aurantiopileus mayaensis was somehow combined into Aurantiporus by Zmitrovich (2018). In our phylogenetic analysis (Fig. 1), the two genera sensu typi stand apart from each other and are clustered in different clades. Nevertheless, A. mayaensis is nested with Aurantiporus albidus Rajchenb. & Cwielong described from Argentina, and both species are characterized by large, watery, and fleshy basidiomata when fresh, shrink and hard when dried which fit well with the concept of Aurantiporus in morphology (Rajchenberg 1995; Ginns et al. 2010). Regarding the available GenBank sequences attributed to Aurantiporus albidus, two Australian specimens (Cui 16664 and Cui 16665) and two Argentinean specimens (CIEFAP-117 and F32) formed two lineages in our phylogeny (Fig. 1). It seems that the Australian samples represent another taxon rather than Aurantiporus albidus. Notably, Aurantiporus albidus stands out microscopically from other Aurantiporus species in its strongly agglutinated generative hyphae covered with hyaline, resinous material and thick-walled, amyloid basidiospores, and may be a distinct species as suggested by Rajchenberg in (1995). However, it is certain that taxa of Aurantiopileus and Aurantiporus s. str. nested in two clades in Meruliaceae.

We thank Prof. Yu-Guang Fan (Hainan Medical University, China) for collecting specimens.