Lichens marins - Myriolecis semipallida forme sur béton.

Myriolecis semipallida forme sur béton.

Myriolecis semipallida forme sur béton.

Description

Thallus not very visible and most often reduced to a crown around the apothecia of somewhat placodioid appearance, 1-2 cm in diameter, upper surface smooth, white, whitish if humid, whitish dirty a little yellowish if dry (or in herbarium), no hypothallus visible but this thallus often rests on a layer of black cyanobacteria. Apothecia most often grouped and tight against each other and covering almost all, or all, of the thallus, more or less sessile, flat, smooth disc, opaline and translucent colorations: yellowish, greenish, brownish, celadon, greyish , pinkish, etc., if wet and fresh but pale yellowish-brown if dry (or in herbarium), net margin, white or dirty white more or less deformed in contact with other apothecia. Pale yellow-brown epithecium, with granules clearly visible in polarized light, soluble in KOH and insoluble in NO3H. 8-spore clavated asci. Hyaline spores, elliptical, simple but sometimes giving the impression of being 1-septate by the presence of 2 guttules, 9-13 x 6-8 µm according to our measurements. Curved filiform conidia: 10-17 x 1 µm. Margin of apothecia: C- or C + yellow, K + yellow, KC + yellow, P-; apothecia disc: K + golden yellow to orange, KC + golden yellow to orange, C + yellow to orange (sometimes weak), P-, apothecia: UV + orange. Taxon coming to the seashore on damp, dirty and poorly lit concrete. Differs from the type by its habitat, its apothecia grouped in clusters and its reduced thallus.

Taxon of the Myriolecis dispersa s.l. group but this last species has negative colored chemical reactions, neighbor of Myriolecis invadens with a larger thallus and darker apothecia discs: dark brownish to blackish with dark blue or blue-green, and more or less pruinose, the latter species being more continental and mountainous.

N.B. Appearance of Myriolecis albescens on limestone but this last species has negative chemical reactions.