Xylographa
A genus of crustose lichens containing a trebouxioid alga; thallus immersed, smooth or sorediate; apothecia usually elongated, tapering to the ends or rounded, sometimes forming dense clusters of small, rounded or contorted segments, the rim thin but persistent, or poorly formed in some species; hymenium formed of more or less straight paraphyses often with a swollen tip, embedded in gel; hypothecium colourless; asci thin-walled or with a modestly thickened tholus, IKI- or + light to medium blue; spores 8 per ascus, oblong, elliptical or ovate, often with a single large oil droplet within.
References: Ryan 2004; Spribille 2006; Spribille & Björk 2008.
| 1a. | Thallus with soredia; apothecia often tightly clustered, 0.2-1 mm long, pink or pale brown; spores …Xylographa vitiligo |
| 1b. | Thallus lacking soredia; apothecia rarely clustered, size various, dark brown, reddish-brown or black; spores various …2 |
| 2a. | Apothecia oblong or elliptical with rounded ends, less than 2 × long as wide, often clustered in chains …Xylographa trunciseda |
| 2b. | Apothecia with pointed ends; at least 2 × long as broad, not in chains …Xylographa parallela |
Xylographa parallela (Ach. : Fr) Behlen & Desberger
Thallus immersed, usually producing a white or creamy white stain in the wood (rarely bark) substrate, or a few tiny granules emerging to the surface; apothecia aligned with the wood grain, more or less evenly spaced, fusiform with the ends blunt to finely tapered, 0.3-2 × 0.2-0.3 mm, the rim thin and persistent or disappearing, coloured like the disc, disc flat to low-convex, matte dark brown, black or reddish brown; rim non-algal; hymenium 60-70 µ high, colourless; upper hymenium dark reddish brown; hypothecium colourless; asci thin-walled except for the thin tholus, IKI+ pale blue; spores elliptical, oblong or ovate, 11-17 × 5-7 µ.
Reactions: Thallus K- or K+ yellow.
Contents: Stictic acid.
Habitat: On conifer wood, rarely on bark or in dripzones. All forested elevations.
Similar Species: Xylographa sibirica is superficially similar, but its apothecia and spores are smaller.
Specimens: Björk 10803, 11644.
Local Status: Common.
Xylographa trunciseda (Th. Fr.) Minks
Thallus immersed, with only a thin layer or a creamy white stain at the surface, lacking soredia; apothecia everpresent, red-brown or dark brown or blackish, 0.2-0.3 × 0.1-0.3 mm, often positioned end to end in short chains up to 1.2 mm long; spores 10-13 × 4-6 µ, elliptical.
Reactions: Spot tests all negative.
Contents: No known lichen substances.
Habitat: On wood of logs, rarely on snags, always within the winter snowpack, lower to middle elevations.
Similar Species: Xylographa parallela also occurs in upper elevation forests, but differs from X. trunciseda in having longer, generally blackish apothecia not joined in chains
Specimens: Björk 8467.
Local Status: Occasional.
References: Foucard (2001).
Xylographa vitiligo (Ach.) J.R. Laundon
Thallus immersed, with only a thin layer or a creamy white stain at the surface, with flat to low-convex soralia 0.2-1 × 0.2-0.4 mm, usually elongated parallel to the grain of the substrate; soredia 20-30 µ wide, often in clusters up to 50 µ wide; apothecia common, light to medium pinkish brown, 0.2-1 × 0.15-0.4 mm, often tightly clustered and contorted into odd shapes by compression; spores 10-14 (‑16.5) × 4-7.5 µ, elliptical.
Reactions: Soredia K+ yellow-orange, PD+ orange.
Contents: Stictic acid and related compounds, perhaps also atranorin and various minor substances.
Habitat: On hard conifer wood, rarely on bark. All forested elevations.
Similar Species:
Specimens: Björk 12874.
Local Status: Common.