After incubation at 21 degrees Celsius under ambient light, a colony with characteristics reminiscent of the order Entomophthorales emerged. It was subcultured and cryopreserved under accession number ARSEF 7942 at the USDA-ARS Collections of Entomopathogenic Fungal Cultures in Ithaca. Under the microscope, the isolate showed clear affinities with Basidiobolus: simple conidiophores tipped with bulbous swellings, and uninucleate conidia that are launched forcibly when pressurized cytoplasm inside the conidiophore is expelled.

Yet several features did not fit any known Basidiobolus species. Most strikingly, after discharge the conidium retains a basal membranous appendage derived from the conidiophore apex, which never separates from the spore. The circumscissile rupture line, the clean break that releases the spore, sits higher on the conidiophore than in Basidiobolus.

And in a feature never before recorded in this group, primary conidia can give rise directly to digitate, finger-like chlamydospores, thick-walled resting structures borne terminally on a single conidiophore. The concatenated alignment comprised 2,136 nucleotide positions, with 894 sites from 28S, 519 from ITS, and 723 from RPB2. The best-fitting models were GTR+F+R4 for 28S and RPB2 and TPM3u+F+R3 for ITS in the maximum likelihood framework, and TrNef+G for 28S and ITS and TIMef for RPB2 in the Bayesian analyses.

The results were unambiguous in one key respect. All recognized Basidiobolus species formed a strictly monophyletic clade with maximal support of 100 percent bootstrap and a Bayesian posterior probability of 1.0. The focal isolate ARSEF 7942, however, segregated entirely from that complex, forming a distinct lineage with support values of 54 percent bootstrap and 0.99 posterior probability.

The bootstrap figure falls below the conventional 70 percent threshold, but the authors note that the lineage's monophyly is corroborated by congruent topologies under both inference methods, by the isolate's clear morphological distinctiveness, and by the absence of shared derived characters with Basidiobolus species. Intriguingly, the still unpublished genus Schizangiella, represented by strains from snakes, emerged as a sister lineage to ARSEF 7942 with strong support of 86 percent and 0.99. On the strength of this combined molecular and morphological evidence, the team established Drechslerosporium as a new genus, named in honor of Charles Drechsler, the mycologist who described many American species of Conidiobolus and Basidiobolus.

The type species, D. cornellii, honors Ezra Cornell, founder of Cornell University. The formal description records slow-growing colonies that are initially pale brown and later fuzzy and white in the center, with colorless mycelium that shows little aerial growth. Primary conidiophores are unbranched, mostly 5.4 to 9.1 micrometers wide, extending 91 to 237 micrometers into the air and terminating in an elongated ellipsoidal propulsive distention 27.1 to 38.3 micrometers long.

The subspherical to obovoid conidia measure 22.2 to 36.3 by 17.3 to 29.2 micrometers and carry the empty membranous remains of the conidiophore apex, mostly cylindrical structures of 4.9 to 9.9 by 4.9 to 7.4 micrometers that stay attached. The discharge mechanism itself is the centerpiece of the taxonomic argument. In typical Basidiobolus species, the conidiophore breaks cleanly at a circumscissile zone at the base of the apical vesicle, and a pressurized blast of cytoplasm expels the conidium, which then separates from the propulsive remnants in flight through eversion of a basal papilla.

This classical mechanism is known as the sporophore rocket. In Drechslerosporium, the rupture occurs anomalously higher, near the top of the apical vesicle, so the discharged conidium permanently retains conspicuous membranous remnants of the conidiophore apex. The conidium lacks a true columella and is delimited by a basal septum that tethers it to those remnants after launch.

The authors designate this arrangement a modified sporophore rocket, one that lacks the papillar eversion seen in its relatives. Secondary conidia appear in two forms: smaller replicas of the primary conidia, discharged in the same violent manner, and elongated capilliconidia, prolate ellipsoids 43.2 to 56.8 micrometers long including an apical beak of 9.1 to 12.4 micrometers that is coated distally with adhesive material for passive dispersal. The digitate chlamydospores, which develop directly from primary conidia under suboptimal conditions within three to five days and measure 38 to 53 by 12.2 to 19 micrometers, represent an autapomorphy, a unique derived trait, unrecorded in any allied taxon.

The genus does share foundational characters with Basidiobolus, including uninucleate primary conidia, similar conidial wall ultrastructure, homologous conidiophore architecture, and the capacity to produce capilliconidia. But the divergent discharge mechanism, historically a key generic-level diagnostic trait among these fungi, together with the darkly pigmented colonies that contrast with the typically hyaline mycelia of all known Basidiobolus species, justified generic separation. The authors note a superficial convergence with Ballocephala, whose discharged propagules also carry the ruptured conidiogenous cell apex, but point out that Ballocephala builds a complex branched conidiophore and has been transferred out of the Entomophthorales to the Kickxellomycotina, whereas Drechslerosporium retains a simple, unbranched conidiophore.

The discovery has broader consequences for fungal classification. Basidiobolus, established in 1886 with the type species B. ranarum, comprises ecologically versatile fungi found in soil, decaying organic matter, and amphibian feces, often dispersed by arthropod vectors, and several species are known to cause subcutaneous and systemic infections in humans. Molecular studies have long complicated the picture: early rDNA analyses showed Basidiobolus diverging significantly from other Entomophthorales and grouping instead with chytrid representatives, while subsequent multilocus and phylogenomic studies produced inconsistent topologies, leaving the genus's higher-order placement unresolved even as its monogeneric family remained entrenched in taxonomy.

The formal recognition of Drechslerosporium required an emended diagnosis of Basidiobolaceae, now defined to include the conidial appendages and digitate chlamydospores. Zygospores, the resting spores characteristic of Basidiobolus, have not yet been observed in D. cornellii, leaving one chapter of its biology still to be written.

Subject of Research: Description of the new fungal genus and species Drechslerosporium cornellii within Basidiobolaceae, based on morphology and multilocus phylogenetics

Article Title: Drechslerosporium cornellii gen. et sp. nov. within the Basidiobolaceae exhibiting unique conidial discharge and digitate chlamydospores

Article References: Nie, Y., & Huang, B. (2026). Drechslerosporium cornellii gen. et sp. nov. within the Basidiobolaceae exhibiting unique conidial discharge and digitate chlamydospores. MycoKeys, 136, 177-191. https://doi.org/10.3897/mycokeys.136.200461

Image Credits: AI Generated

DOI: 10.3897/mycokeys.136.200461

Keywords: Drechslerosporium cornellii, Basidiobolaceae, Basidiobolus, fungal taxonomy, Entomophthorales, conidial discharge, chlamydospores, multilocus phylogeny, new genus, mycology, Cornell, plant detritus