Bulbothrix


Bulbothrix is a genus of lichen-forming fungi in the family Parmeliaceae. Established in 1974 by the American lichenologist Mason Hale as a segregate from the genus Parmelia, Bulbothrix comprises about 40 accepted species as of 2025. These foliose lichens are distinguished by their characteristic black, bulb-tipped hairs along the lobe edges and are found roughly equally divided between the Old World and New World, growing predominantly on trees in lowland rainforests and shrublands.

Taxonomy

Bulbothrix was circumscribed by the American lichenologist Mason E. Hale in 1974 with Bulbothrix semilunata as the type species. Hale established Bulbothrix as a segregate from Parmelia, specifically from the subgenus Parmelia section Imbricariae subsection Bicornutae. He noted that Bulbothrix is readily recognised by its characteristic black marginal bulbous, which distinguishes it from related genera. Hale observed that the species are roughly equally divided between the Old World and the New World, occurring predominantly on trees in lowland rainforest and in scrub or secondary forests at lower elevations in subtropical to temperate regions.
This genus is synonymous with Bulbothricella, and with Bulborrhizina.

Description

Bulbothrix develops a foliose thallus that lies closely attached to the bark or rock it inhabits. Its are narrow to moderately broad and usually press against one another, though in a few species such as B. isidiza they may overlap slightly. Along the lobe edges run short, bulb-tipped hairs called, a feature that gives the genus its name. The upper surface is grey because it contains atranorin, a common lichen product, and may show pale blotches ; some species bear tiny outgrowths or small side lobes, but none produce soredia or pores for gas exchange. Microscopically the upper consists of a of tightly packed fungal cells coated by a thin, perforated, and the cell walls contain the rare polysaccharide isolichenan. Beneath this, a loosely woven white—or occasionally pigmented—medulla stores nutrients, while the pale tan to black undersurface anchors itself with simple to repeatedly branched root-like rhizines that match the background colour.
Sexual reproduction occurs in apothecia that sit on the thallus surface and are either somewhat stalked or directly attached. Their cup-shaped are unperforated, range from pale to dark brown, and may be ringed by small black swellings embedded in the rim, though in some species this corona is absent. Each ascus contains eight ellipsoidal or occasionally curved, two-horned ascospores measuring roughly 6–15 × 4–8 μm. Asexual propagules are generated in flask-shaped pycnidia, either sunken in the thallus or raised on the same bulbae that flank the apothecia; these structures release slender, spindle-shaped conidia about 5–9 × 1 μm that disperse the fungal partner alone. Chemical tests detect a suite of secondary metabolites—including sphaerophorin, various β-orcinol depsidones, usnic acid, and dibenzofuran derivatives.

Species

Hale accepted 29 species of Bulbothrix in his original circumscription of the genus in 1976., Species Fungorum accept 37 species of Bulbothrix.
  • Bulbothrix apophysata
  • Bulbothrix asiatica
  • Bulbothrix australiensis
  • Bulbothrix bicornuta
  • Bulbothrix bulbillosa – Galápagos Islands
  • Bulbothrix caribensis
  • Bulbothrix cassa – Brazil
  • Bulbothrix cinerea
  • Bulbothrix goebelii
  • Bulbothrix isidiza
  • Bulbothrix johannis
  • Bulbothrix klementii
  • Bulbothrix lacinia
  • Bulbothrix lacinulata – Brazil
  • Bulbothrix laeviuscula
  • Bulbothrix lobarica – Brazil
  • Bulbothrix lordhowensis
  • Bulbothrix lyngei
  • Bulbothrix mammillaria
  • Bulbothrix megapotamica
  • Bulbothrix microscopica – Australia
  • Bulbothrix pseudocoronata
  • Bulbothrix pseudofungicola – Brazil
  • Bulbothrix queenslandica
  • Bulbothrix regnelliana – Brazil
  • Bulbothrix semilunata
  • Bulbothrix silicisrea – Brazil
  • Bulbothrix sipmanii – Guyana
  • Bulbothrix subscortea
  • Bulbothrix subtabacina
  • Bulbothrix tabacina
  • Bulbothrix thomasiana
  • Bulbothrix ventricosa
  • Bulbothrix viatica – Brazil
  • Bulbothrix yunnana – China