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Six new species and reports of Hydnum (Cantharellales) from eastern North America

Abstract Five species of Hydnum have been generally recognized from eastern North America based on morphological recognition: H.albidum, H.albomagnum, H.repandum and varieties, H.rufescens, and H.umbilicatum. Other unique North American species, such as H.caespitosum and H.washingtonianum, are either illegitimately named or considered synonymous with European taxa. Here, seventeen phylogenetic species of Hydnum are detected from eastern North America based on a molecular phylogenetic survey of ITS sequences from herbarium collections and GenBank data, including environmental sequences. Based on current distribution results, sixteen of these species appear endemic to North America. Of these, six species are described as new: H.alboaurantiacum, H.cuspidatum, H.ferruginescens, H.subconnatum, H.subtilior, and H.vagabundum. Geographic range extensions and taxonomic notes are provided for five additional species recently described as new from eastern North America. A new name, H.geminum, is proposed for H.caespitosum Banning ex Peck, non Valenti. Overall, species of Hydnum are best recognized by a combination of morphological and molecular phylogenetic analyses. Taxonomic descriptions are provided for seventeen species, including epitype designations for H.albidum, H.albomagnum, and H.umbilicatum, taxa described more than 100 years ago, and molecular annotation of the isotype of H.washingtonianum. Photographs and a key to eastern North American Hydnum species are presented.


Introduction
Hydnum L: Fr (=Dentinum Gray) is a genus of ectomycorrhizal (ECM) mushroom-forming fungi found primarily in temperate forests of Asia, Australia, Europe, and North America. Until recently, only twelve species of Hydnum were commonly accepted worldwide. Initial phylogenetic studies of European Hydnum revealed higher than expected taxonomic diversity in the genus, with thirteen molecularly recognized clades masquerading under four morphologically-defined species names (Grebenc et al. 2009), which have since been described as new species (Olariaga et al. 2012, Vizzini et al. 2013, Niskanen et al. 2018. Following a global survey of diversity in the genus which estimated 31 species worldwide based on molecular phylogenetic analysis (Feng et al. 2016), additional taxonomic work in Europe and North America has raised the global species count to 34 (Buyck et al. 2017, Niskanen et al. 2018, which is estimated to be less than half of the total number of Hydnum species (Niskanen et al. 2018). This previously overlooked diversity may be due to morphological stasis in evolution of basidiome morphology and lack of attention to regional characterization of the Hydnum flora in locations outside Europe.
Hydnum, in its original Linnean concept, contained all species of mushroom-forming fungi with a spinose hymenophore (e.g., Fries 1821). Indeed, over 900 names have been attributed to the genus per Index Fungorum (www.indexfungorum.org). However, molecular phylogenetic analysis showed that the spinose hymenophore has evolved independently many times in distantly related taxa (Hibbett et al. 1997). As a consequence, most species formerly contained in Hydnum have been moved to other genera. Species of Hydnum in the contemporary sense (Donk 1956) and typified by H. repandum L.:Fr. are united by their smooth hyaline basidiospores, white to orange basidiomes, and stichic basidia, in which the meiotic spindle is vertically oriented (Donk 1933, Maas Geesteranus 1971, Restivo and Petersen 1976, Pine et al. 1999. Ecologically, Hydnum form ECM associations with a variety of vascular plant species including members of Pinaceae (Agerer et. al 1996), Myrtaceae (McNabb 1971), Fagales (McNabb 1971, Feng et. al 2016, Niskanen et al. 2018, Salicaceae (Niskanen et al. 2018), Malvaceae (Niskanen et al. 2018), and Dipterocarpaceae (Lee et al. 2002). The genus is distributed mostly in temperate areas, with a few reports from tropical and subtropical forests in southeast Asia (Lee et al. 2002, Feng et al. 2016) and the neotropics (Garibay-Orijel et al. 2006, Sarmiento and Fontecha 2013, Feng et al. 2016, Niskanen et al. 2018. Previous analysis of global Hydnum diversity revealed the presence of six distinct clades of Hydnum in eastern North America, only one of which also occurs on another continent (Feng et al. 2016). Currently, five species have been described from eastern North America: H. albidum Peck, H. albomagnum Banker, H. aerostatisporum Buyck, D.P. Lewis & V. Hofst., H. caespitosum Banning ex Peck (non Valenti), and H. umbilicatum Peck. Banker (1906) and Harrison and Grund (1987) recognized six species of Hydnum from across North America in their taxonomic treatments. Of those species that occur in eastern North America, four were described over one hundred years ago, and the application of those names has not been clarified in light of molecular phylogenetic analyses. Here, we resolve those species names by taxonomic revision of type specimens and DNA sequencing of contemporary collections, as well as document Hydnum species diversity and distribution in eastern North America. Seventeen species are treated here, of which six are described as new. A taxonomic key to species from eastern North America is included. lected as the best-fit model for Bayesian inference (BI) analysis in PartitionFinder 2.1.1 (Lanfear et al. 2016). BI analyses were performed using MrBayes 3.2.6 (Ronquist and Huelsenbeck 2003); the global analysis ran for 10 million generations with sampling every 1000 th generation. Following global BI tree visualization, clades that did not contain sequences from eastern North America were pruned to form a second tree figure for easier graphical representation. Maximum Likelihood (ML) analysis was performed on the pruned dataset in RAxML 8.2.8 (Stamatakis 2014) using 1000 bootstraps under a GTRGAMMA model of nucleotide substitution following the RAxML user manual recommendation. BI analysis of the pruned data set ran for 5 million generations with sampling every 500 th generation.
The resulting phylogenies were visualized in FigTree v.1.4.3 (http://tree.bio.ed.ac. uk/software/figtree/). Mislabeled sequences were omitted, as well as Hydnum from the southern hemisphere due to high levels of sequence divergence (Feng et al. 2016). Sistotrema alboluteum was chosen as an outgroup based on Feng et al. (2016). DNA alignments and tree files are available at TreeBase (submission 22888).
Species are recognized here as monophyletic groups that differ in morphology, ecology, and/or geographic distribution.

Results
119 ITS sequences were produced for this study (Suppl. material 1). For the BI analyses, the average standard deviation of split frequencies reached below 0.01 after 4 million generations (global phylogeny) and 2 million generations (pruned phylogeny), so the first 40% of sampled trees were discarded as the burn-in for each analysis. Posterior probabilities (PP) for each analysis were calculated from 12002 samples from two independent runs for both the global and pruned analyses. In each case the potential scale reduction factor (PSRF) convergence diagnostic reached a value of 1.0 for all parameters, indicative of sufficient sample size.
The global phylogeny contained 397 sequences and 61 species-level clades (Suppl. material 2). Species-level clades containing sequences from eastern United States and Canada are colored red in the global circle tree (Fig. 1). PP ≥ 0.95 for nodes of these clades are denoted with an asterisk. The pruned version of the global tree, including taxon tip labeling information, is shown in Fig. 2. Four major clades of North American Hydnum were recovered, each with ML bootstrap support ≥ 70%. These are labeled by subgenus: Alba, Pallida, Hydnum, Rufescentia (Niskanen et al. 2018  chosen based on morphological consistency and geographic proximity to sites containing holotypes. We were able to sequence partial ITS regions from two historical Peck collections labeled H. albidum, but based on morphology those specimens represent a separate, larger, white species that we describe here as H. vagabundum.
A total of sixteen species-level monophyletic groups from eastern North America were recovered, representing ten described and six undescribed species. One additional species, H. geminum, was not represented by any modern collections, and thus its phylogenetic position is unconfirmed. Below, taxonomic descriptions are presented for eastern North American species by subgenus. Of the recovered species, only one eastern North American Hydnum, H. mulsicolor, also occurs outside North America. This result is consistent with recent work that showed eastern North American clades of Hydnum are largely endemic (Feng et al. 2016, Niskanen et al. 2018. None of the species studied display a clear preference for tree host genus. Many occupy a wide geographic range within eastern North America, with three species (H. albidum, H. subtilior, H. vagabundum) also found in Central America. One species, H. washingtonianum, occurs in both eastern and western North America.
Basidia in Hydnum were consistently suburniform, often undulating, and tapered to a narrow pedicel. Basidium shape was not considered a diagnostic trait and thus omitted from taxonomic descriptions below. Basidiospores of Hydnum were inamyloid and acyanophilous (Hall and Stuntz 1971). Morphological variation across Hydnum was low compared to other genera, with few variable microscopic features. As a consequence, species varied by differences in basidiospore size and shape, number of sterigmata, and pileipellis elements. Several taxa in subg. Rufescentia were nearly morphologically indistinct from one another and could be identified in the field only by a combination of morphology and distribution/habitat data. Even so, ITS sequencing is necessary to confidently identify those species.
Basidiospores 4.5-5.2-6 μm × 3-4-4.5(5) μm, Q=(1.05)1.07-1.33-1.58(1.74) (n=72/5), subglobose to broadly ellipsoid, smooth, thin-walled, hyaline in KOH. Basidia 28-36(40) × 6-7(8) μm with 5-6(7) sterigmata. Pileipellis an interwoven cutis, hyphae smooth, cylindrical, thin-walled, mostly 3-6 μm wide. Clamp connections present. Discussion. Hydnum albidum was originally described from New York by Peck (1887) and produces small white to cream-colored basidiomes with small subglobose to broadly elliptic basidiospores. In the protologue Peck distinguishes H. albidum from H. repandum by the smaller basidiomes and spores, as well as white coloration. In a later description Peck (1897) added that H. albidum is an edible but uncommon species "uniformly colored in all its parts". Of the two small white species of Hydnum that occur in eastern North America ( Fig. 3A-D), both H. albidum and H. alboaurantiacum have similarly small subglobose basdiospores ( Fig. 6A-B). However, H. alboaurantiacum quickly stains bright orange within minutes wherever handled, while H. albidum stains much less vividly brown-orange, sometimes only hours after handling. In addition, H. alboaurantiacum is only known from the southeastern US. While we were unable to successfully sequence DNA from the holotype of H. albidum, several collections from the region of the type locality are consistent with the morphology of the holotype of H. albidum, and one of these is designated as an epitype.
In addition to the holotype, there are several other historical collections made by Peck to which he applied the name H. albidum. Based on basidiospore measurements alone, it is clear three of the eight collections have much larger spores than H. albidum. We successfully sequenced partial ITS from two of those three collections, which matched modern specimens from Texas, New York, and Honduras belonging to a species more closely related to H. repandum (see discussion of H. vagabundum).
Hydnum repandum var. album (Quél.) Rea is a European variety, the name of which has been widely applied in North America (Coker and Beers 1951, Smith et al. 1981, Harrison and Grund 1987, Roody 2003. The description of H. repandum var. album by Roody (2003) appears to refer to H. subtilior, while displaying a photo of what is perhaps H. albidum. However, the spores of H. albidum are smaller than the 7-8.5 × 5.5-7 μm listed by Roody (2003), Harrison and Grund (1987), Smith et al. (1981), and Coker and Beers (1951). Thus, the American concept of H. repandum var. album is best interpreted as H. subtilior, described below. Etymology. alboaurantiacum (L.) white-orange, referring to the coloration of the basidiomes, which stain bright orange.
Distribution Discussion. Hydnum alboaurantiacum has probably been mistaken for the closely related H. albidum due to the initial pale white coloration and similar basidiospore size and shape. However, H. alboaurantiacum quickly stains bright rusty orange on all parts of the basidiomes where handled, whereas H. albidum slowly stains a lighter brownorange hue. In addition, H. alboaurantiacum often displays a larger and more stout stature than H. albidum. The two species are readily distinguished as separate clades in Fig. 2. Hydnum alboaurantiacum is known only from the southeastern US and appears derived from a grade of Central American taxa including the recently described H. zongolicense (Niskanen et al. 2018). Description. Pileus 60-110 mm wide, irregularly round, irregularly convex to plano-convex or uplifted; surface dull, glabrous with adhering debris, uneven and sometimes pitted in places, cream white (4A4) with patches of cottony white, becoming light tan in age (10 YR 6/4); margin thin, wavy to slightly lobed, incurved when young then raised in age. Spines 1-6 mm long, brittle in mass, adnate to subdecurrent, white to cream white (4A3-5A3). Stipe 20-40 × 13-20 mm thick, central or eccentric, clavate, occasionally split in two towards the apex; surface smooth, concolorous with spines, if bruising then only very slightly an hour or more after handling ("Yellow-Ocher" to "Ochraceous-Tawny"). Context fleshy, white, unchanging when cut. Odor mild or slightly acidic at first, then pleasantly fruity like apricots when stored in foil. Taste mild.

Hydnum albomagnum Banker, Bulletin of the Torrey Botanical
Basidiospores 5.5-6.2-7 μm × 3-3.8-5 μm, Q=1.24-1.66-2.07(2.17) (n=45/3), ellipsoid to broadly ellipsoid, smooth, thin-walled, hyaline in KOH. Basidia 38-46 × 5-6 μm with 4-5(6) sterigmata. Pileipellis a tightly interwoven cutis, hyphae smooth, cylindrical, thin-walled, mostly 2.5-5 μm wide. Clamp connections present. Discussion. The original description of Hydnum albomagnum by Banker (1901) was based solely on dried material. As mentioned in the protologue, this species has a shorter stipe and overall stouter appearance than other Hydnum. In addition, mature basidiomes are much larger than other whitish small-spored species. Hydnum albomagnum also has more strongly ellipsoid spores (Q values averaging 1.66) than other species. Historically, H. albomagnum has been less frequently collected than other pale species of Hydnum, perhaps because the basidiomes are often buried underneath layers of needle and leaf litter and thus overlooked. As basidiomes emerge from the ground, leaf litter remains stuck to the matt glabrous surface of the pileus, masking its appearance. This characteristic, along with the creamy white coloration, large basidiome size, and small ellipsoid spores, makes this one of the easier Hydnum species to identify. DNA sequencing of the type specimen of H. albomagnum was not successful; however, all modern collections reported under this species name have identical ITS sequences and match the morphology of the original species description. An epitype is chosen from Tennessee material, closest to the location of the holotype from Alabama.
Distribution Discussion. Hydnum subtilior is a common species in the southeastern U.S. found in deciduous and mixed forests with a variety of tree associates, often in deep layers of leaf litter. Environmental sequencing has recovered this species from Quercus root tips in central Mexico (García-Guzmán et al. 2017). The stipe is usually longer than the diameter of the pileus, and the overall coloration can range from light cream-yellow to peach or tan. The best diagnostic features for this species are the coloration and often elongated stature in combination with broadly ellipsoid spores averaging 8 × 6.3 μm. In addition, the context of fresh basidiomes stains orange throughout within five minutes when cut in half (Fig. 3H).
Other Discussion. Hydnum vagabundum is a large whitish species in subgenus Hydnum. Two collections of this species at NYS from the late 1800s and early 1900s were misidentified as H. albidum by Peck but feature distinctly larger basidiospores than the holotype of H. albidum. In addition, basidiomes of this species are much larger and fleshier than those of H. albidum. Partial ITS sequences obtained from Peck's specimens match two extant collections from New York and Texas, as well as GenBank sequences from western Honduras (HM639268, HM639267; Sarmiento and Fontecha 2013). In Honduras this species can be found in May and June, where it is a common edible (Sarmiento and Fontecha 2013 Description. Pileus up to 40 mm wide, subplane, slightly depressed, thin, irregular; surface glabrous, "subviscose", wrinkled when dry, pale orange. Spines 3-5 mm long, terete, slender, acute, decurrent half way down the stipe, pale yellow but nearly white when fresh. Stipe up to 40 × 5-10 mm, subcylindrical, tapering slightly towards the base, central or slightly eccentric, pale orange. Context fleshy. Basidiospores 7-7.7-8.5 μm × 6-6.8-7.5(8) μm, Q=1.04-1.13-1.22 (n=40/2), subglobose to broadly ellipsoid, smooth, thin-walled, hyaline in KOH. Basidia 31-41 × 7.5-8.5 μm with 4 sterigmata. Pileipellis hyphae not reviving. Clamp connections present.
Distribution. Western North America and eastern Canada -British Columbia, Washington (type), California (GenBank GU180269, MG972632), and Newfoundland and Labrador.
Ecology. On ground in coniferous woods. December. Discussion. Hydnum washingtonianum, originally described from the Puget Sound region of Washington, is characterized by the pale orange pileus, yellowish decurrent spines, small globose basidiospores, and tough flesh. The species was considered synonymous with H. repandum by Maas Geesteranus (1964) and Hall and Stuntz (1971). However, we were able to produce a partial ITS sequence from the isotype (GenBank MH379846), which does not match European H. repandum sequences. Thus, we consider this species as an autonomous taxon with a mostly northern geographic distribution in North America. Phylogenetic analysis of the ITS sequence confirms this species from Washington, British Columbia, California, and Newfoundland and Labrador. Hydnum washingtonianum is associated with coniferous forests on both coasts, and one environmental sequence (Gen-Bank GU180269) recovered this species on root tips of Pinus muricata in California.
Hydnum neorepandum, a recently described species from Newfoundland and Labrador (Niskanen et al. 2018), has an ITS sequence that differs by a single base pair from that of the isotype of Hydnum washingtonianum. The morphology of both protologues is also in agreement. Thus, we consider H. neorepandum a taxonomic synonym of H. washingtonianum.
Distribution Discussion. Hydnum ferruginescens is known only from three occurrences in the southeastern U.S. This species is similar to H. magnorufescens, which has similarly sized basidiomes but slightly larger spores and is known from Europe and Asia. Description. Pileus (20)30-100 mm wide, irregularly round or sometimes reniform, convex to plano-convex, becoming funnel-shaped in age, sometimes with slit or umbilicus forming over stipe, surface dry, glabrous, subzonate when young, then cracking to coarsely scurfy in age, bright to medium brownish orange ("Xanthine Orange" to "Orange Rufous"), paler when young ("Salmon-Orange"), often cracking in age to reveal lighter color of context ("Pale Pinkish Buff"); margin incurved and entire when young, then wavy, irregular or degraded in age, discoloring slightly darker after handling. Spines 1-9 mm long, close, mostly awl-shaped but occasionally spathulate, adnate to subdecurrent, buff to peach ("Light Buff" to "Pinkish Buff"). Stipe 25-80 × (3)7-25 mm, central or eccentric, equal or slight bulbous at base in younger specimens, smooth, often with white hazy or cottony patches overlaid on surface, cream white to pale orange in younger basidiomes, then darker tan orange with age, discoloring very slightly brownish orange when handled. Context cream to peach colored, firm, sometimes hollow with age, unchanging after 5 minutes when cut in half. Odor mild or sweet at first, then pleasantly fruity like apricots when stored in foil. Taste mild or weakly acrid.
Ecology. In hardwoods of Quercus, Carya, Ulmus or mixed woods including Betula, Picea, Tsuga. June to October. Discussion. Hydnum aerostatisporum is a commonly encountered species in the eastern U.S. It has been found primarily in hardwoods and mixed woods including conifers at high and low elevations on both sandy and non-sandy soils. The vibrant medium to dark orange pileus transitions from smooth in young specimens to conspicuously cracked and scurfy in age, often becoming funnel-shaped, occasionally with a hole or umbilicus. The stipe frequently becomes darker tan-orange in age, which is unusual in other medium-sized orange-pileate species of Hydnum. Basidiomes, particularly older specimens, often have patches of hazy white on the stipe surface.
Hydnum aerostatisporum was recently re-described as a new species from Quebec -H. subrufescens (Niskanen et al. 2018). The ITS sequence of the holotype of H. subrufescens differs from that of the holotype of the earlier described H. aerostatisporum by seven base pairs, but H. subrufescens does not form a well-supported monophyletic group in our phylogenetic analyses and recognition of H. subrufescens as a separate species would render H. aerostatisporum paraphyletic (Fig. 2). The morphology of both is consistent, including the similarly sized globose to subglobose spores. For these reasons, we consider H. subrufescens a taxonomic synonym of H. aerostatisporum. Description. Pileus 12-25 mm wide, irregularly round to slightly reniform, convex to plano-convex, surface dry, glabrous, orange ("Zinc Orange" to "Xanthine Orange"), sometimes cracking in age near central depression; margin incurved and entire or slightly degraded. Spines 1-3 mm long, adnate, cream-colored, at times thick and somewhat flattened. Stipe 15-35 × 5-8 mm, central or eccentric, equal or widening at base, firm, smooth, white to cream, lightly staining ochre to medium brownish orange ("Mars Yellow" to "Orange Rufous") where handled. Context not observed. Odor and taste mild.
Distribution. Eastern North America -Newfoundland and Labrador (type, Gen-Bank KX388681) and North Carolina.
Ecology. In conifer forest with Abies fraseri. August to September. Discussion. Hydnum canadense is only known from high-elevation and higher latitude conifer forests in North Carolina and eastern Canada. The North Carolina collection was found among several basidiomes of H. umbilicatum. Hydnum canadense can be distinguished from H. umbilicatum by the 3-5 sterigmata (versus 2-4 sterigmata in H. umbilicatum) and ITS sequence divergence. Hydnum canadense differs from the closely related H. mulsicolor by the association with conifers and larger spore size. Another closely related species, H. submulsicolor, is morphologically indistinguishable from H. canadense according to Niskanen et al. (2018), and ITS sequencing is likely necessary to reliably differentiate it from H. canadense. The spores of the North Carolina collection of H. canadense reported here are more globose with a lower average Q value than that of the Newfoundland and Labrador collections reported by Hydnum quebecense Niskanen & Liimat., Mycologia 110: in press (2018) Fig. 5K Type. CANADA. Québec: Saint-Donat (46.3000;-74.2000), in conifer-dominated forest (Tsuga, Abies, Picea, Betula, and Populus), 5 Sep 2010, anonymous, T. Niskanen 10-064 (holotype H7043948, isotype K(M)248983, isotype NY).
Discussion. This species is closely related to H. umbilicatum but is characterized by the apparent habitat preference for Sphagnum bogs. The holotype from Quebec (KX388662) was described among Sphagnum in association with conifers and northern hardwoods (mainly Picea, but also Tsuga, Abies, Betula, Populus).
Discussion. This species is known only from a single basidiome collected in New York. The description is drawn from the original collection notes. It is closely related to H. subconnatum but differs from it by the smaller spore size, shorter stipe, and association with Sphagnum. It is recorded from the same locality and habitat as H. quebecense but differs from that species by ITS sequence and smaller spores. We refrain from describing the taxon as new until confirmed by additional collections and sequence data. Etymology. subconnatum (L.), born together, in reference to the fused stipe bases of multiple basidiomes.
Distribution Discussion. Hydnum subconnatum is known from the southeastern U.S. in a range of low elevation mixed forests such as oak-pine or hemlock-pine mixed with oak and beech. All known specimens are reported under 1000 m elevation. Basidiomes can occur in caespitose clusters with the stipe bases and two or more pilei fused together. The pileus coloration is highly variable, however, ranging from deep orange to pale peach and fading to tan towards the margin, making this a difficult species to distinguish at a glance. Hydnum caespitosum Banning ex Peck (non H. caespitosum Valenti), described from Maryland, occurs "at roots of trees and near old stumps" and is much paler in coloration, depicted by Banning in her painting as a yellowish species. Furthermore, our examination of the holotype of H. caespitosum revealed that basidiospores are much smaller in that species than in Hydnum subconnatum. The new name H. geminum is proposed below for H. caespitosum Banning ex Peck.
Distribution. Eastern U.S. -Maryland (type). Ecology. In clusters at the roots of trees and near old stumps, August to September. Discussion. The new binomial H. geminum is introduced to replace the illegitimate name H. caespitosum Banning ex Peck, which is a later homonym of H. caespitosum Valenti. The gross morphological description here is reproduced from Banker (1906) after reformatting for style, and measurements appear to be based on dried specimens. Peck's protologue, Banning's painting, and Banker's notes depict a species best characterized by the overall yellowish color, short decurrent spines, flavescent or yellowing flesh, mild taste, and broadly elliptic to subglobose basidiospores that are mostly 6.5 × 5 μm in size. Although specimens of H. subconnatum (described above) may share the similar caespitose or clustered habit, it differs from H. geminum by the peach-orange to dark orange-brown pileus, longer nondecurrent spines, and a stipe that bruises orange-brown, not yellow. In addition, the basidiospores of H. subconnatum are larger than in H. geminum -8.5-9.5 × 7.5-9 μm. Basidiomes of H. subtilior sometimes have an overall pale yellow tone and stain when bruised or cut in half, but basidiospores are smaller in H. geminum, and the overall basidiome stature of the holotype appears much stouter than in the generally slender H. subtilior.
Upon examining the holotype of H. caespitosum, we found that basidiomes had very short spines (<1 mm) with very few spores and basidia. This aligns with Peck's notes indicating he did not obtain spores and suggests the holotype consists of immature basidiomes.
We have not yet recorded H. geminum in eastern North America. Banker (1906) refers to a collection made by Earle from Connecticut now housed at NCU (NCU-F-0012251). We have not re-examined this collection, but Banker describes it as somewhat darker than the type.

Key to species of Hydnum in eastern North America
Note that the five species in couplet 17 are most reliably distinguished by phylogenetic analysis of ITS sequences.