Cryptocalciella humilis Mandolini, Szedlacsek & Peintner sp. nov. Etymology. From Latin humilis (low, humble) — referring to the nutrient-poor, cold habitat where this species originated from and the low nutrient requirements this species has. Furthermore, the name indicates this species’ courtesy, which allows it to carry selected bacteria on its hyphae. This enables it to potentially achieve something greater together: colonizing these difficult habitats and making them habitable for others. Diagnosis. Cryptocalciella humilis colonies are fast-growing (PDA, 20 ° C), mycelia develop abundant clusters of terminal and intercalar bulbous gemmae. Large, unbranched sporangiophores are formed in bundles, resembling a crystal chandelier, sporangiophores (262) 373–758 (1107) × (28) 37–57 (76) µm, tapered below the tip with a slightly pronounced apophysis and collarette after spore liberation. Each sporangiophore produces an apical, spherical multispored sporangium; sporangiospores smooth, ovoid to phaseoliform, (4.8) 7.6–10.6 (16.7) × (3.2) 4.2–5.9 (10.7) µm, with a hyaline episporal layer. pH-optimum 8–10, no growth at 25 ° C and above. Typus. Italy, Trentino, Marmolada glacier forefield, Mesozoic latemar limestone and dolomite sandy-rocky sediments with no or scattered vegetation cover (Arabis alpina L., Arabis caerulea Haenke, Cerastium uniflorum Thom. Ex. Rchb., Poa minor Gaudin) 46.441896, 11.859656, 2760 m a. s. l., 18. Aug. 2021, soil collected by E. Mandolini (Mandolini et al. 2025) (holotype IBF 20210222, culture ex-type CBS 154075, GenBank Acc. No. ITS PV 434959). Description. Colonies fast growing, with an increase of 6.4–7.3 mm per day on PDA (20 ° C) (Fig. 6), mycelium dense, white, with varying growth patterns ranging from foamy concentric rings to extended wave-like lobes to flowery shapes with varying rosette sizes (Fig. 2). Aerial mycelium usually not very pronounced. Cultures on poor media (LCA and SEA) with fast radial growth, but mainly in the substrate, with only fine and plain aerial mycelium and without elaborate growth patterns with the only exception on LCA where colonies develop a thin white ring of accumulated bulbous gemmae on the external colony margin, occasionally also the centre (Figs 2, 3). Colonies with a foul acidic odor over time. Hyphae coenocytic, usually without septa, hyphal diameter variable, ranging from 2.9–4.7 mm (n = 100), sometimes thinning out into very fine hyphae of 1–2 µm diam., hyphae single or as hyphal bundles, grow straight or in spiral form, and then resulting in dense, intermingled hyphal areas. Branching irregularly, formation of septa only in cases when the cytoplasm is resorbed and hyphae or branches persist as empty tubes, in this case often also with several consecutive septa, indicating a stepwise resorption of the content. Bulbous gemmae develop terminal on unseptated hyphae, very abundant, frequently branching, forming clusters of bulbs, predominantly formed on the surface of the colony, (11.9) 14.3–18.5 (22.5) × (11.5) 13.8–17.6 (21.2) µm (n = 100) (Fig. 3). Gemmae also formed intercalary (5.2) 10.6–16.0 (18.8) × (4.6) 10.7–15.7 (18.3) µm (n = 50). Both gemmae (intercalar and terminal) also occurring submerged in the agar, appearing after about one week, but latest after 14 days on PDA at 16 ° C. Large areas of older cultures consisting of nest of bulbous structures only. Nuclei located irregularly in the mycelium and present also in the bulbous gemmae (Fig. 3). When hyphae with bulbous structures are abandoned, the bulb is left behind empty as well (Fig. 3). No detachment of bulbs detected. Oil-like vesicles in the cellular content observable in both vegetative hyphae and gemmae (intercalar and terminal), especially when grown on PDA. On LCA condensed and large nests of those bulbous structures can be located only in the white ring area of the colony. Sporulation observed after several months, once the cultivation temperature was lowered from 16 ° C to 4 ° C during the incubation period. Simple, erect, unbranched sporangiophores with (262) 373–758 (1107) µm (n = 39) in length, protruding from the substrate, usually originating from nests of gemmae; formed in bundles with an appearance resembling a crystal chandelier or a flower bouquet (Fig. 5). Sporangiophore base reaching a diameter of (28) 37–57 (76) µm (n = 48), tapering to (17.0) 21.9–33.5 (42.7) µm (n = 53) below the tip, and ending in a slightly pronounced apical inflation (apophysis). Sporangia single, mostly spherical, with (78) 88–138 (167) µm (n = 21) diameter, ochraceous before maturation with a discreet columella (5.6) 9.2–19.7 (26.5) µm (n = 53) in height after spore liberation. Peridia deliquescing, leaving a conspicuous collarette after aperture, with (21.5) 31.5–52.0 (62.1) µm (n = 53) in diameter. Upon spore release, masses of sporangiospores conflux into large drops (Fig. 4). Sporangiospores (4.8) 7.6–10.6 (16.7) × (3.2) 4.2–5.9 (10.7) µm (n = 211) in size, irregular, ovoid to phaseoliform, smooth, and surrounded by a hyaline episporal layer, often remaining in conjunction with other spores, giving the impression of having a slightly sticky surface, at least after the spore liberation (Fig. 4). Sporangiophores and sporangia sometimes encircled by solitary hyphae, leaving a net of hyphae as a cap after spore liberation. Both sporangia and spores are strongly cyanophil, sporangiophores appear dextrinoid with Melzer’s reagent (iodide). Detailed drawings of Cryptocalciella humilis are presented in Fig. 5. Growth requirements. Optimum temperature 16 ° C – 20 ° C, with a daily radial increment of 6.4–7.3 mm. Growth was observed in a temperature range from 4 ° C – 20 ° C. No growth at and above 25 ° C. Optimum pH 8–10; daily radial increment of up to 8.6 (± 0.1) mm (16 ° C). Additional strains examined. Austria, Upper Austria, Ramsau am Dachstein and Obertraun, sandy-rocky mesozoic limestones and dolomites sediments with rare patchy vegetation (Arabis alpina, Arabis pumila, Cerastium uniflorum, Poa minor, Heliosperma pusillum (Waldst. & Kit) Rchb., Saxifraga aphylla Sternb.) from the forefield of Hallstätter glacier forefront 47.48765, 13.618747, 2250–2700 m a. s. l., 03. 07. 2021, soil collected by E. Mandolini, and U. Peintner (Mandolini et al. 2025) (IBF 20210223, CBS 154062, GenBank Acc. No. ITS PV 435009). Habitat and distribution. All isolates originate from calcareous glacier sediment at the earliest stages of soil development in glacier forefields (<20 years of ice-free sediment). The type specimen was cultured from barren ground close to the glacier ice front of the Marmolada Glacier in the Dolomites, Italy. Additional strains originate from the Hallstätter Ferner glacier in the Dachstein area, Austria. Based on data mining, Cryptocalciella humilis appears to be rare in other habitats. Notes. This is currently the only representative of this genus, but it appears to be frequent in the two investigated, geographically distant calcareous glacier forefield habitats (Dachstein and Griessen) based on isolation-driven screening (Szedlacsek et al. 2025). Phylogenomic analyses clearly show that it represents a distinct lineage with a sister-group relationship to Gamsiella (Fig. 1). The closest reported morphological similarity to the striking sporangiophores of C. humilis is found in Dissophora globulifera (O. Rostr.) Vandepol & Bonito. The latter produces sporangia in dense tufts. Sporangiophores are 500–1000 µm long and possess a columella; sporangia are globose and 40–48 µm in diameter. Sporangiospores are globose, delicately echinulate, and 6–7 µm in diameter. D. globulifera has been isolated from agricultural soils in Europe and Japan, and environmental sequences indicate that it is a globally widespread taxon associated with forest soils (SH 1019593.10 FU). Based on sequence similarity, D. globulifera is not closely related to Cryptocalciella but instead shows a sister-group relationship to Bonitomyces. Cryptocalciella also shows some resemblance to Mortierella rostafinskii Brefeld, as originally depicted by Brefeld (Kuhlman and Hodges Jr. 1972). However, M. rostafinskii differs by the absence of a columella and by the fact that only a few (2–4) sporangiophores arise from a hyphal mass consisting of short branches, rather than from bulbous cells. Spores are oval to cylindric, regular, and thin-walled. Additionally, mature sporangia and empty sporangiophores of C. humilis show a high morphological resemblance to Aquamortierella elegans Embree & Indoh (Embree and Indoh 1967). Both genera develop large, erect, non-septate sporangiophores that taper from base to tip, possess an apophysis, and form large spherical sporangia, leaving a distinct peridial collarette after spore liberation. However, sporangiospore morphology differs markedly. In A. elegans, sporangiospores are reniform to sinuate allantoid with vermiform appendages, whereas C. humilis produces ovoid to phaseoliform, smooth sporangiospores surrounded by a hyaline episporal layer. Double-walled sporangiospores are an unusual character in Mortierellaceae and have previously been reported only for Lunasporangiospora chienii (P. M. Kirk) Vandepol & Bonito and Mortierella strangulata van Tieghem (van Tieghem 1875).

Published as part of Mandolini, Edoardo, Szedlacsek, Sophie, Abramczyk, Beniamin, Szucs, Attila, Staykova, Anastasiya, Seybold, Anna, Knapp, Magdalena, Pawłowska, Julia, Ladurner, Peter & Peintner, Ursula, 2026, Cryptocalciella – a new Mortierellaceae genus from Alpine glacier forefields, pp. e 177912 in IMA Fungus 17 on page e177912, DOI: 10.3897/imafungus.17.177912