Gilled Bolete

The Gilled Bolete is a taxonomic curiosity made visible in the field. Everything about the fruit body says bolete, from the dry velvety cap and the olive-tinted spore deposit to the soft yellow flesh, yet the underside carries thick golden gills instead of a tube layer.

It belongs to Phylloporus, a genus firmly nested within the Boletaceae whose species have independently reduced the pore layer to gills. Close inspection often reveals the fungus's ancestry: the gills are frequently forked, cross-veined and interconnected near the stipe, and in some specimens the connections form shallow pores at the very top of the stipe.

The genus is a favourite teaching example of convergent evolution, showing that gills have evolved repeatedly in unrelated fungal lineages and that hymenium shape is a poor guide to relationship. Phylloporus rhodoxanthus is the familiar eastern North American species; Phylloporus pelletieri fills the same niche in Europe.

Cap

Convex then flat or slightly depressed, 3–9 cm across. The surface is dry and distinctly velvety to finely tomentose, often cracking into small areolae in age or dry weather, sometimes revealing paler yellow flesh in the fissures. Colour ranges through reddish-brown, cinnamon, olive-brown and dull maroon-brown, sometimes fading to tan.

Gills

The defining feature: thick, waxy-looking, widely spaced and decurrent, running well down the stipe. They are bright golden to chrome yellow, often forked near the margin and conspicuously cross-veined and anastomosing near the stipe, occasionally forming shallow pore-like pockets there. In some collections they bruise slowly blue-green where damaged.

Stipe

Slender, 3–8 cm tall and up to 1.5 cm thick, equal or tapering downwards and often curved. It is yellowish, streaked and overlaid with reddish-brown to cinnamon fibrils, sometimes finely ridged at the apex where the gills run down. There is no ring and no volva, and the basal mycelium is yellowish.

Flesh and spore print

Soft, pale yellow to whitish, sometimes flushed reddish under the cap cuticle, unchanging or slowly staining faint blue-green. The spore print is olive-yellow to yellowish-brown, matching the boletes rather than the gilled fungi it superficially resembles.

Phylloporus rhodoxanthus is mycorrhizal with hardwoods, especially oaks, and also occurs with conifers in mixed stands. It grows on the ground, most often singly or in small scattered groups on mossy woodland banks, along trail cuttings and on sloping ground with thin litter.

Fruiting runs from midsummer into autumn. The species is widespread across eastern North America, with related taxa through Central and South America and eastern Asia; in Europe the equivalent species is Phylloporus pelletieri, a fungus of beech and oak woodland on acid soils.

Despite its gills, this is an ectomycorrhizal fungus in the same functional guild as the pored boletes, forming hyphal mantles over the fine roots of oak and other partners and extending emanating hyphae into litter and soil. It contributes to the tree's uptake of phosphorus and nitrogen and receives carbohydrate in return.

The reduction of tubes to gills within a pored lineage is thought to reflect selection for a larger spore-bearing surface in a thin, quickly maturing fruit body; the persistent cross-veins and pore-like pockets near the stipe are relics of the ancestral tube layer. Fruit bodies are small, soft and short-lived, decaying within days.

The False Chanterelle (Hygrophoropsis aurantiaca) has thin, crowded, repeatedly forked orange gills, a soft dry orange-buff cap and a white spore print. True chanterelles (Cantharellus) have blunt, shallow, vein-like ridges rather than knife-edged blades, pale spore prints and firm white flesh.

The Brown Roll-rim (Paxillus involutus) is larger with a strongly inrolled, felty cap margin, crowded soft gills that separate easily from the cap flesh and stain rusty brown on handling, and a brown spore print. Chroogomphus species have decurrent gills but ochre to salmon caps, a viscid surface and dark smoky-grey to blackish spore prints. Where the gills are thick, widely spaced, golden yellow and cross-veined over a dry velvety brown cap with an olive-yellow print, the fungus is a Phylloporus.