A previously unnamed fungal lineage living in orchid roots in Kochi Prefecture, Japan, has been cultured and formally named Reflexicalyptrales, establishing an entirely new order within Basidiomycota.

Molecular phylogenetics using a four-locus dataset places Reflexicalyptra japonica as a strongly supported, early-diverging lineage within Agaricomycetes, sister to Tremellodendropsidales and distant from existing orders.

Ultrastructural analysis revealed a unique dolipore septum with a multi-pored, perforate cap that reflexes outward, a configuration not previously documented in Basidiomycota.

ITS sequence divergence between Reflexicalyptra and Tremellodendropsidales (63–76%) is well below the typical 80% threshold used to separate fungal orders, supporting the creation of a new order.

The formal taxonomy includes the order Reflexicalyptrales, family Reflexicalyptraceae, and genus Reflexicalyptra, with Reflexicalyptra japonica as the type species; types II–IV remain undescribed pending further material.

The organism, initially detected as an anonymous dark taxon in Nervilia nipponica root pelotions since 2013, was cultured from the base of a single inflorescence and verified as the same lineage (uAX type I) in two pure culture strains.

Public sequence databases reveal closely related environmental sequences from Europe, Africa, the Americas, Estonia, and South Africa, indicating the lineage is globally distributed and likely primarily saprotrophic in soils rather than strictly mycorrhizal.

The discovery underscores that well-studied soils can hide major lineages of the fungal tree of life and that integrating culture, morphology, physiology, and phylogeny can yield comprehensive taxonomic naming in a single publication.

A previously unnamed fungal lineage living in orchid roots in Kochi Prefecture, Japan, has been cultured and formally named Reflexicalyptrales, establishing an entirely new order within Basidiomycota.

The study highlights a gap between sequencing and taxonomy: without cultures and physical specimens, many dark taxa remain unnamed; Reflexicalyptrales provides both living isolates and cryopreserved type material to satisfy taxonomic requirements.

Physiological and morphological characterization showed two strains grow best at 25°C, tolerate 10–30°C, stop at 5–35°C, have binucleate hyphae without clamp connections, and produce numerous sclerotia-like structures on sawdust media, potentially containing calcium oxalate crystals.