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Bryostigma muscigenum (Th.Fr.) Frisch & G. Thor

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Moseflekklav.
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Bryostigma muscigenum collected from mosses at Skåras in Sokndal (TRH-L-24060).

Bryostigma muscigenum is a species growing over mosses, bark and even rock. It is characterized by minute, distinctly convex, black apothecia growing on a scurfy-granular thallus with a chlorococcoid photobiont. The colorless spores are 1-septate. It is difficult to distinguish from similar species without microscopical examination.

Moseflekklav.
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Bryostigma muscigenum collected from Leucodon sciuroides near Hedrum in Larvik (O-L-68088).

Description

Thallus

The thin thallus is olive-grey to grey and minutely scurfy-granular. When well-developed, the granules are 25–50 µm in size. The thallus margin is not determinate. The photobiont is a chlorococcoid alga.

Fruitbodies

The apothecia are distinctly convex, sitting on the thallus, black with often an olive-green hue, and without pruina. They are rounded to short elliptical in shape, 0.05–0.3 mm and 60–100 μm tall.

The epithecium is 5–8 µm tall, and greenish or reddish brown. It is formed by 2–3 layers of periclinally arranged, dark-walled tips of the paraphysoids.

The hymenium is colorless or pale green and 25–40 μm tall.

The hypothecium is reddish brown and up to 70 μm tall.

The scanty paraphysoids are ca 1 μm wide.

The asci are clavate, with stipe, 18–27 × 11–13 µm in size, and 8-spored.

The spores are colorless, obovoid to slipper-shaped, and often slightly constricted at the septum. They are 8–12 × 2.5–4 μm in size and divided by 1 transverse septum.

Anamorph

Pycnidia are brownish black, immersed in the thallus, and ca 40 µm in size. The wall is pale brown. The rod-shaped conidia are 3–4 × ca 0.5 μm in size.

Chemistry

The thallus does not react with C, K, KC, Pd, or UV (C–, K–, KC–, Pd–, UV–). Lichen secondary compounds have not been detected by TLC. 

The hymenium reacts I+ red and KI+ blue. A KI+ blue ring structure has been observed in the asci.

The brown pigment in the apothecia and in the wall of the pycnidia changes to greenish in K solution.

Moseflekklav.
Creative Commons Attribution Share-alike | Andreas Frisch

Bryostigma muscigenum collected from Leucodon sciuroides near Hedrum in Larvik (O-L-68088).

Ecology

Bryostigma muscigenum grows in natural and anthropogenic habitats on a variety of substrates including mosses on trees and rocks, bark of deciduous and coniferous trees, and even on shaded siliceous rocks. It has been collected on Leucodon sciurioides and other bryophytes in Norway, but most Norwegian findings are from trees in humid forests including myrsine-leaved willow (Salix myrsinifolia), wooly willow (Salix lanata) and wych elm (Ulmus glabra). In Trøndelag, it is reported mainly from Norway spruce (Picea abies) in humid boreal spruce forests including rainforests. 

Distribution in Norway and the Nordic countries

Bryostigma muscigenum is occurs throughout Norway but is not often collected. In the Nordic countries, it is also known from Denmark, Finland and Sweden.

Global distribution

Outside the Nordic Countries, Bryostigma muscigenum is widely distributed in temperate and boreal Europe and North America. 

Moseflekklav.
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Bryostigma muscigenum collected from mosses at Ørdalsfossen in Kvam (O-L-222325).

Similar species

Several superficially similar species occur in Norway. The common Arthonia apatetica has slightly larger and less convex apothecia, an unpigmented to pale straw-colored hypothecium and larger spores, 11–16 × 3.5–5 µm.

Arthonia fusca can be distinguished from populations growing on rock by paraphysoids that do not form 2–3 layers of periclinally arranged hyphae in the epithecium and larger ascospores, 11–18 × 4–7 µm.

Arthonia tenellula also lacks periclinally arranged hyphae in the epithecium and the tips of the paraphysoids in the epithecium lack dark brown pigment caps and plaques. The occurrence of this species in Norway is uncertain.

Arthonia ligniariella has a I– and KI–hymenium and lacks a KI+ blue ring structure in the asci. 

Arthonia patellulata has generally lager apothecia, 0.2–0.7mm in size, a dark brown hypothecium, and paraphysoids that do not form 2–3 layers of periclinally arranged hyphae in the epithecium.

Arthonia mediella is easily distinguished by spores with 3 transverse septa and often larger, pure black apothecia up to 0.8 mm in size.

Vierflekklav.
Arthonia apatetica (A. Massal.) TH. Fr.
Olivenflekklav.
Arthonia fusca (A. Massal.) Hepp
Feil: bilde mangler.
Arthonia ligniariella Coppins
Ospeflekklav.
Arthonia patellulata Nyl.
Skurvflekklav.
Arthonia mediella Nyl.

Remarks

This species is difficult to identify without microscopical examination. In Great Britain, it is currently named Bryostigma lapidicola (Taylor) S.Y. Kondr. & J.-S. Hur (Cannon et al. 2020). The older synonym, Arthonia lapidicola (Taylor) Branth & Rostr., has been used in Norway until recently for another species that is now Arthonia fusca. These names should not be mixed. 

Literature

Cannon P, Ertz D, Frisch A, Aptroot A, Chambers S, Coppins BJ, Sanderson N, Simkin J and Wolseley P (2020). Arthoniales: Arthoniaceae. Revisions of British and Irish Lichens 1: 1–48.

Poelt J and Döbbeler P (1979). Bryostigma leucodontis nov. gen. et spec., eine neue Flechte mit fast unsichtbaren Fruchtkörpern. Plant Systematics and Evolution. 131:211–216.

Wirth V, Hauck M and Schultz M (2013). Die Flechten Deutschlands, vol. 1+2. Ulmer, Stuttgart. 1244s.