Strigula


Strigula is a genus of lichen-forming fungi in the family Strigulaceae.

Taxonomy

The genus was circumscribed in 1823 by the English mycologist Elias Magnus Fries.
The taxonomy of the genus has undergone significant revisions based on multilocus phylogenetic analyses. Originally defined broadly to include species growing on various substrates, research revealed that foliicolous species formerly placed in Strigula actually form six well-defined clades that warranted recognition as separate genera. The foliicolous species have been reallocated into the following genera:
  • Strigula – Includes the type species S. smaragdula and is characterized by thickened, bright green to grey-green thalli with a Cephaleuros photobiont, carbonized perithecial walls, small to medium-sized ascospores, and macroconidia with short to medium-sized appendages.
  • Serusiauxiella – A newly recognized genus with species that have a Trentepohlia photobiont and unique macroconidial appendages that rapidly grow to substantial lengths when observed in microscopic mounts.
  • Raciborskiella – Includes hypophyllous species with very thin, bluish grey thalli, carbonized perithecial walls, large ascospores, and terminal appendages on ascospores.
  • Puiggariella – Features species with distinctive thallus morphology displaying white papillae and non-carbonized perithecial walls.
  • Racoplaca – Comprises species with thin, finely lobed thalli of olive-brown to dark olive-green color which feature a characteristic thin black line along the lobe margins.
  • Phylloporis – Contains supracuticular species with a Phycopeltis photobiont, carbonized perithecial walls, and comparatively short asci and small ascospores.

Description

Strigula, in its currently defined narrower sense, is a genus of lichen-forming fungi characterized by its distinctive foliicolous growth pattern. These lichens form subcuticular thalli, meaning they grow beneath the cuticle of leaves, infiltrating between cell layers rather than simply growing on the surface. The thalli of Strigula are typically thickened, with a characteristic bright green to grey-green coloration. They form rounded patches with entire to margins on leaf surfaces. Strigula species develop a symbiotic relationship with a specific algal partner in the genus Cephaleuros, which provides the lichen with carbohydrates through photosynthesis.
Reproductive structures include perithecia that are partially immersed in the thallus, appearing as small, basally immersed and apically erumpent black dots. The perithecial wall is, appearing jet-black in cross-section. The perithecia contain asci that are with a short and narrow.
Each ascus produces eight, which are arranged in one to two rows within the ascus. The ascospores are, single-septate, colorless, and relatively small to medium-sized. Strigula also produces asexual reproductive structures called pycnidia, which contain with short to medium-sized gelatinous appendages that extend only slowly when observed in laboratory preparations.

Species