Hemithecium

  1. Home
  2. Wiki

Hemithecium
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Lecanoromycetes
Order: Graphidales
Family: Graphidaceae
Genus: Hemithecium
Trevis. (1853)

Hemithecium is a genus of lichen-forming fungi in the family Graphidaceae.[1] These lichens form pale grey-white to yellow-olive crusts on tree bark and are characterized by straight to weakly curved fruiting bodies with charcoal-black walls that create sharp contrasts against the surface, along with distinctive spine-tipped filaments lining their interior chambers. The genus has a pantropical distribution, growing on shaded tree trunks and large branches in primary or lightly disturbed evergreen forests, where their marked sensitivity to canopy opening makes them practical indicators of intact, moisture-rich woodland habitat.

Taxonomy

[edit]

The genus was circumscribed by Vittore Benedetto Antonio Trevisan de Saint-Léon in 1853.[2]

Description

[edit]

Hemithecium forms a pale grey-white to yellow-olive crust (thallus) that lacks a true cortex and is often dotted with minute crystals. Its lirellae are straight to weakly curved, frequently pruinose, and bordered by thick, charcoal-black walls—the excipulum is carbonised throughout, causing the script-like slits to contrast sharply with the thallus. The clear hymenium is non-inspersed and lined with short, spine-tipped periphysoids; these spinulose filaments are a hallmark of the genus. Eight hyaline ascospores develop in each Graphis-type ascus; they become transversely septate to strongly muriform, measure roughly 30–100 × 10–25 μm, remain iodine-negative (I–), and are enveloped by a thin halo that persists in potassium hydroxide solution. Most species contain norstictic acid or stictic acid, occasionally together with trace depsidones of the protocetraric series.[3]

The coexistence of fully carbonised lirellae, spinulose periphysoids, a non-inspersed hymenium and large, I– muriform spores sets Hemithecium apart from superficially similar script lichens. In Acanthothecis the margins remain pale; Fissurina lacks spinulose filaments; and Carbacanthographis shares the black excipulum but possesses minute, often iodine-positive spores. Within Hemithecium itself two informal species groups are recognised: a "large-spored" complex (e.g., H. radicicola) with spores exceeding 60 μm long, and a "medium-spored" set (e.g., H. flabillense) with spores 30–50 ΜM long, yet both uphold the diagnostic character combination described above.[3]

Ecology

[edit]

The genus is pantropical, extending from lowland Amazonian and West-African rainforests through Southeast Asian dipterocarp stands to montane cloud forests of New Guinea and north-eastern Australia. All known species are corticolous, occupying shaded trunks and large branches in primary or only lightly disturbed evergreen forest; their marked sensitivity to canopy opening means several taxa disappear rapidly after logging, making Hemithecium a practical indicator of intact, moisture-rich woodland habitat.[3]

Species

[edit]

As of June 2025, Species Fungorum (in the Catalogue of Life) accepts 22 species of Hemithecium.[4]

References

[edit]
  1. ^ Wijayawardene, Nalin; Hyde, Kevin; Al-Ani, LKT; S, Dolatabadi; Stadler, Marc; Haelewaters, Danny; et al. (2020). "Outline of Fungi and fungus-like taxa". Mycosphere. 11: 1060–1456. doi:10.5943/mycosphere/11/1/8.
  2. ^ Trevisan de Saint-Léon, V. (1853). Spighe e Paglie Scritti Botanici Varj del Cavaliere Professore Vittore Trevisan [Ears and Straws: Various Botanical Writings of Cavaliere Professor Vittore Trevisan]. Vol. 1. p. 11.
  3. ^ a b c Lücking, Robert; Rivas Plata, Eimy (2008). "Clave y guía ilustrada para géneros de Graphidaceae" [Key and illustrated guide to genera of Graphidaceae]. GLALIA (in Spanish). 1 (1): 1–39.
  4. ^ "Hemithecium". Catalogue of Life. Species 2000: Leiden, the Netherlands. Retrieved 19 June 2025.
  5. ^ a b c d e Sharma, Bharati O.; Khadilkar, Pradnya; Makhija, Urmila (2012). "New species and new combinations in the lichen genera Fissurina and Hemithecium from India". The Lichenologist. 44 (3): 339–362. doi:10.1017/S0024282911000752.
  6. ^ Jia, Z.F. (2011). "A preliminary study of Hemithecium and Pallidogramme (Graphidaceae, Ostropales, Ascomycota ) from China". Mycosystema. 15: 870–875.
  7. ^ a b c d e f Adawadkar, B.; Makhija, U. (2005). "Some trans-septate species of the genera Hemithecium and Platythecium from India". Mycotaxon. 92: 387–394.
  8. ^ Jagadeesh Ram, T.A.M.; Sinha, G.P. (2009). "New species of Graphis and Hemithecium (lichenized Ascomycetes) from Eastern Himalaya, India". Mycotaxon. 110: 31–35. doi:10.5248/110.31.