Termitomyces arjunii, a Novel Termitophilic Agaric from a Private Organic Garden in Mapusa, Goa, India

Termitomyces arjunii Kamat, Gupte & Gupte, sp. nov. is described from a single basidiocarp collected at a private organic garden in Karaswada, Mapusa, Goa, India, in close association with the co-occurring Termitomyces heimii population documented at this site (Kamat et al., 2026). The pileus is small, 2.7-3 cm diameter, buff to desert-tan (Orange and Brown dominant hues, Section 4), with a central umbo bearing a knobby, irregular, dark brown to blackish melanized perforatorium - the drilling organ through which the basidiocarp emerges through the termite mound substrate and overlying soil - its surface frequently bearing adherent soil particles bound by a viscous, colourless extracellular bioglue secreted during drilling. Lamellae are emarginate, crowded, pale pink to buff-pink, attached to a diagnostically narrow (<2 mm) white, depressed, smooth collarium. The stipe is central, cylindrical to subradicate, arising from a short, fragile pseudorrhiza (commonly under 10 cm and readily sheared during collection), with a broadly capitulate apex leaving a smooth, concave hollow at the pileus-stipe junction where the pseudorrhiza detaches. Examination of teased lamellar tissue (fresh material, aqueous Congo red, x40-x100) resolved polymorphic (elliptical, globose, and obovoid), colourless, thin-walled, frequently guttulate basidiospores; abundant, polymorphic calcium oxalate mycoliths (granular clusters, druses, a rosette/floret form, and an elongate prismatic form) distributed throughout the lamellar tissue; turgid, Congo red-positive cheilocystidia together with morphologically similar but Congo red-negative, sterile spherocysts filled with lipid-like inclusions - a cell type not previously described in the genus and treated here as an additional novel taxonomic character; clavate, tetrasporic basida with basidioles; a cellular subhymenium bearing lipid-positive storage globules, a character previously documented by the corresponding author across several smaller-bodied Goan Termitomyces species; parallel hyphal arrangement in the hymenophoral trama; and a hydrophobic, shield-like surface topography of the pileus, umbo, and perforatorium, consistent with hydrophobin-mediated water repellency reinforced by melanin. Digital chromotyping of the pileus and lamellae (Image Colour Summarizer, SDK33), based on 215 uniquely named colours resolved across four replicate images (70, 61, 50, and 34 per image), showed a percent-weighted colour profile dominated by Orange and Brown hues in both structures (pileus 65.7%, lamellae 84.3%; colour-group Bray-Curtis dissimilarity = 0.186), with weighted mean CIELAB values of L* = 71.3, a* = 7.0, b* = 18.4 for the pileus and L* = 68.1, a* = 7.5, b* = 22.7 for the lamellae (cross-structure ΔE76 = 5.4). Named-colour diversity was higher in the pileus (Shannon H' = 2.98; Hill number 2D = 14.5) than the lamellae (H' = 2.59; 2D = 10.2), while full named-colour Bray-Curtis dissimilarity was of comparable magnitude within replicate images of a single structure (0.321-0.400) and between the two structures (mean 0.386), a pattern corroborated by principal coordinates ordination and indicating that photographic replicate variability was not negligible relative to the pileus-lamellae colour difference in this single-specimen dataset. Termitomyces arjunii is identified as a new species on the basis of a distinctive combination of macromorphological characters - the narrow, depressed collarium, the knobby irregular perforatorium with its adherent soil/bioglue coating, and the capitulate stipe apex with matching pileus hollow - not previously reported together within the genus.