Fusicastoreum R.A. Day, Davoodian, T. Lebel & Castellano, in Cao et al., Fungal Diversity 132: 579 (2025)
Index Fungorum Number: IF 853778; Mycobank Number: MB 853778; Facesoffungi Number: FoF 17092
Etymology – Refers to the fusoid spores, and the morphological resemblance of the basidiomata to the related genus Castoreum (Mesophelliaceae).
Type species – Fusicastoreum pisiglareum R.A. Day, Davoodian, T.W. May, T. Lebel & Castellano.
Basidiomata globose to subglobose; peridial surface brown, black or white, encrusted with roots, soil particles and debris, surface somewhat lumpy from debris to more or less even, base sometimes flattened, without conspicuous attachment or emanating hyphae. Peridium composed of three layers; epicutis brown to black and white, melanised, incorporating soil and debris and occasionally plant roots; mesocutis off-white to pale brown, occasionally staining pinkish-brown, often incorporating plant roots, plant roots appearing to be flanked by brown-colored filaments; subcutis the thinnest of the three layers and colored deep brown to black. Gleba pale yellow-beige to sienna in color, locules spherical to sinuous during development, becoming elongate at maturity and powdery. Trama narrow, pale cream strands in young basidiomata, indistinct in mature basidiomata. Odor camphor or naphthalene, occasionally fungoid, sweet, or acetone. Epicutis dark brown, nearly opaque; occasionally incorporating soil particles; of hardened, melanised hyphae in a melanised matrix; hyphae, densely packed, arrangement difficult to ascertain given degree of melanisation, though where apparent appearing as tangled hyphae, compactly woven to well-spaced, organised in rough bundles. Mesocutis hyaline; hyphae compactly interwoven, ± parallel to outer surface, terminal cells occasionally appearing inflated; incorporating plant roots among hyphae. Hyphal coils occasionally present. Subcutis of hardened, melanised hyphae; colored as epicutis above though slightly less melanised; hyphae very densely packed to loosely interwoven, arranged in variously oriented bundles to somewhat radially arranged. Trama hyaline to whitish; hyphae tangled. Basidia two-spored; sterigmata inconspicuous to small. Spores fusoid, smooth; base truncate, apex acuminate; hyaline to faint yellow-beige in color. Utricle absent.
Habit and Habitat – Fusicastoreum is hypogeal, solitary, sometimes caespitose, scattered or in groups beneath leaf litter and up to 10–15 cm of topsoil. Fusicastoreum species occur in a variety of open eucalypt woodlands including young to medium age stands of Eucalyptus sieberii [SAY (Stand Age Young) = 5–15yrs; SAM (Stand AgeMature) = 20–30yrs], mallee eucalypt (Kangaroo Island, South Australia), Eucalyptus globulus (Tasmania), Eucalyptus diversicolor and Eucalyptus marginata (Western Australia).
Notes – In reporting results of a study of ectomycorrhizal fungi on rehabilitated bauxite mines in the Jarrahdale region of Western Australia, Gardner and Malajczuk (1988) listed “Castoreum camphoratum Trappe & Malajczuk sp. nov.” without further information. This designation was also used by Hilton (1989). Dell et al. (1990) described in some detail the morphology of mycorrhizal associations between Eucalypts and certain sequestrate fungi, including “Castorium [sic] camphoratum nom. ined.” Claridge et al. (2000) described the diversity of sequestrate fungi in an area of south-eastern Australia finding more than 200 species in numerous genera, amongst which 18 were undescribed. The novel genera were “tentatively” referred to by designations, one of which was “Fusicastoreum” which was listed as containing one novel species (un-named). Consequently, various collections in Australian fungaria are labelled as either “Castoreum camphoratum”, “Fusicastoreum” sp. or “Fusicastoreum camphoratum”. None of these fungarium names were validly published, as they lacked a description or a diagnosis and citation of a type specimen.
A recent phylogenetic study of the Hysterangiales by Davoodian et al. (2021) distinguished approximately 30 novels but unnamed genera worldwide. In this study, specimens from three collections labelled as “Castoreum camphoratum” and one labelled “Castoreum sp.” fell within a novel genus designated as provisional genus 3; two further “Castoreum sp.” collections from New South Wales fell within the sister clade of provisional genus 26. Following examination of additional fungarium collections from a broader geographic area, and subsequent analyses of morphology and molecular data, provisional genus 26 was found to sit within a clade that we formally recognize as Fusicastoreum gen. nov. This new genus incorporates collections originally placed under the provisional genera 3 and 26. Fusicastoreum can be distinguished from the genus Castoreum by the lack of gummy hyphae within the peridium, the lack of a robust basal rhizoid (which is often present in Castoreum), generally smaller basidiomata, a strong odor (of naphthalene or camphor), and fusoid, smooth spores lacking an utricle.
Key to the species of Fusicastoreum
1: Mesocutis 240–450 µm thick; peridium even in thickness and arrangement surrounding gleba; occurring on Kangaroo Island, South Australia.—F. arenarium.
1: Mesocutis 400–1500 µm thick; peridium uneven in thickness surrounding gleba; occurring in other regions of Australia. —2.
2: Mesocutis containing hyphal coils towards interior; mean spore length 10.8 µm; occurring in southern Western Australia. —F. occidentale.
2: Mesocutis without hyphal coils; mean spore length > 11.5 µm; occurring in southeastern Australia. —3.
3: Mean spore length 11.6 µm; peridium distinctly wavy in cross section; subcutis 60–90 µm thick; glebal locules spherical to sinuous when young.—F. pisiglareum.
3: Mean spore length 12.1 µm; peridium somewhat wavy; subcutis 30–50 µm thick; glebal locules appearing as wavy, elongate, recessed striae radiating from gleba center. —F. trappei.
Species