Fungalpedia – Note 3327, Wallemiomycetes

 

Wallemiomycetes Zalar, de Hoog & Schroers, Antonie van Leeuwenhoek 87(4): 322 (2005).

Citation when using this data: Wijayawardene NN et al. 2024 – Fungalpedia.

Index Fungorum, Faceoffungi, MycoBank, GenBank.

Classification: Wallemiomycotina, Basidiomycota, Dikarya, Fungi.

Sexual morph: Basidiomata absent; Basidia singly or in clusters, irregular in shape, arising from primary cells with a probasidium; single sterigmata or sterigmata-like cells present; basidiospores produced by some genera; single basidiospore in one basidium; globose, rarely subglobose; hirsute; hyaline; double-walled; browning on maturity (Nguyen et al. 2013). Asexual morph: hyphomycetous. Conidiophores solitary or aggregated, unbranched, erect or sometimes sympodial, smooth-walled, and little constricted below the apex. Conidiogenous cells continuing from conidiophores, verruculose, cylindrical, biaxially extending, disarticulating basipetally, four arthrospore-like conidia. Conidia single-cell, verruculose or spherical, short cylindrical, thick-walled, and pale brown (Zalar et al. 2005; Jančič et al. 2015; Díaz‑Valderrama et al. 2017).

Life modes and distribution: The members of Wallemiomycetes are cosmopolitan in distribution and are xerophilic and halophilic in nature. The members are airborne and found to be associated with solar salts, salt crystals, dried plant parts such as hay and seeds, dried food, and are also responsible for food spoilage and agricultural aerosols (Zalar et al. 2005; Díaz‑Valderrama et al. 2017; Zajc and Gunde-Cimerman 2018). Some strains are known to cause subcutaneous skin infections in humans (de Hoog et al. 2000) and hypersensitivity pneumonitis (farmer’s lung disease), caused by Wallemia sebi (Lappalainen et al. 1998; Roussel et al. 2005).

Notes: The class Wallemiomycetes was introduced by Zalar et al. (2005) and is one of the smallest classes of Basidiomycota. Matheny et al. (2006) attempted to resolve the phylogenetic position of Wallemiomycetes using nuclear protein-coding genes. Zhao et al. (2017) tried to resolve the phylogenetic obscurity of the class based on the concepts of molecular data. 

The class Wallemiomycetes is placed in phylogenetic trees in slightly different ways depending on which gene regions are analysed and which phylogenetic inference method is used (Zalar et al. 2005; Matheny et al. 2006). Analyses of the parsimony of the nrDNA data reveal that Wallemiomycetes is an early diverging branch of the Basidiomycota and that it occupies a basal position close to Entorrhizomycetidae (Matheny et al. 2006). He et al. (2024) confirmed that Wallemiomycetes belongs to the subphylum Wallemiomycotina. The class comprises two orders, Geminibasidiales and Wallemiales (Wijayawardene et al. 2022a; He et al. 2024).

Some members of Wallemiomycetes are medicinally important taxa. Wallemia sebi causes allergies, bronchial asthma, farmer’s lung disease (in humans), chronic ulcerative skin lesions, and fatal livestock toxicosis (fide Cole and Samson 1979; Hanhela et al. 1995; Lappalainen et al. 1998, 2012; Reboux et al. 2001; Roussel et al. 2005; Zajc and Gunde-Cimerman 2018). Wallemia muriae causes farmer’s lung disease and bronchial asthma in humans (fide Zajc and Gunde-Cimerman 2018). Wallemiomycetes mellicola causes phaeohyphomycosis on the foot in immunocompetent human (Zajc and Gunde-Cimerman 2018).

Type order: Wallemiales Zalar, de Hoog & Schroers, Antonie van Leeuwenhoek 87(4): 322 (2005).

Type family: Wallemiaceae R.T. Moore, Rhizoctonia Species, Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control (Dordrecht): 20 (1996).

Type genus: Wallemia Johan-Olsen, Skr. VidenskSelsk. Christiania, Kl. I, Math.-Natur. (no. 12): 6 (1887).

Type species: Wallemia ichthyophaga Johan-Olsen [as ‘ichthiophaga’], Skr. VidenskSelsk. Christiania, Kl. I, Math.-Natur.(no. 12): 6 (1887).

Other accepted species: Species Fungorum – search Wallemiomycetes.

 

References

Cole GT, Samson RA. 1979 – Patterns of development in conidial fungi. Pitman Publ. Co., London, San Francisco, Melbourne.

de Hoog GS, Guarro J, Gene´ J, Figueras MJ et al. 2000 – Atlas of clinical fungi, 2nd ed. Centraal bureauvo or Schimmel cultures/Universitat Rovirai Virgili, Utrecht/Reus.

Díaz-Valderrama JR, Nguyen HDT, Aime MC. 2017 – Wallemia peruviensis sp. nov., a new xerophilic fungus from an agricultural setting in South America. Extremophiles 21:1017–1025.

Hanhela R, Louhelainen K, Pasanen A. 1995 – Prevalence of microfungi in Finnish cow barns and some aspectsof the occurrence of Wallemia sebi and Fusaria. Sc J Work Environ Health 21:223–228.

He MQ, Cao B, Liu F, Boekhout T et al. 2024 – Phylogenomics, divergence times and notes of orders in Basidiomycota. Fungal Divers.

Jančič S, Nguyen HD, Frisvad, Zalar P et al. 2015 – A Taxonomic Revision of the Wallemia sebi Species Complex. PLoS ONE 10(5):e0125933.

Lappalainen MHJ, Hyvärinen A, Hirvonen MR, Rintala H et al. 2012 – High indoor microbial levels are associated with reduced Th1 cytokine secretion capacity in infancy. Int Arch Allergy Immunol 159:194–203.

Lappalainen S, Pasanen AL, Reiman M, Kalliokoski P et al. 1998 – Serum IgG antibodies against Wallemia sebi and Fusarium species in Finnish farmers. Ann Alergy Astma Immunol 81:589–592.

Matheny PB, Gossmann JA, Zalar P, Kumar TA et al. 2006 – Resolving the phylogenetic position of the Wallemiomycetes: an enigmatic major lineage of Basidiomycota. Botany 84:1794–1805.

Nguyen HD, Nickerson NL, Seifert KA. 2013 – Basidioascus and Geminibasidium: a new lineage of heat-resistant and xerotolerant basidiomycetes. Mycologia 105(5):1231–1250.

Reboux G, Piarroux R, Mauny F, Madroszyk A et al. 2001 – Role of molds in farmer’s lung disease in eastern France. Am J Respir Crit Care Med. 163:1534–1539.

Roussel S, Reboux G, Dalphin JC, Bardonnet K et al. 2005 – Microbiological evolution of hay and relapse in patients with farmer’s lung. Occup Environ Med 61(1):3e.

Wijayawardene NN, Hyde KD, Dai DQ, Sánchez-García M et al. 2022a – Outline of Fungi and fungus-like taxa – 2021. Mycosphere 13:53–453.

Zajc J, Gunde-Cimerman N. 2018 – The Genus Wallemia-From Contamination of Food to Health Threat. Microorganisms 6:46.

Zalar P, Sybren de Hoog, G, Schroers HJ et al. 2005 – Taxonomy and phylogeny of the xerophilic genus Wallemia (Wallemiomycetes and Wallemiales, cl. et ord. nov.). Antonie Van Leeuwenhoek 87:311–328.

Zhao RL, Li GJ, Sánchez-Ramírez S, Stata M et al. 2017 – A six-gene phylogenetic overview of Basidiomycota and allied phyla with estimated divergence times of higher taxa and a phyloproteomics perspective. Fungal Divers 84:43–74.

 

Entry by

Nalin N. Wijayawardene, Center for Yunnan Plateau Biological Resources Protection and Utilization, College of Biological Resource and Food Engineering, Qujing Normal University, Qujing, Yunnan 655011, P.R. China, Tropical Microbiology Research Foundation, 96/N/10, Meemanagoda Road, 10230 Pannipitiya, Sri Lanka, Department of Bioprocess Technology, Faculty of Technology, Rajarata University, Sri Lanka

 

Published online 2 October 2026

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