Henssenia subglaucella Ertz & R. S. Poulsen 2017, spec. nov.
Creators: name: Ertz, Damien
name: Poulsen, Roar S.
name: Charrier, Maryvonne
name: Søchting, Ulrik
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Fungi
Ascomycota
Lecanoromycetes
Peltigerales
Koerberiaceae
Henssenia
Henssenia subglaucella

description: Henssenia subglaucella Ertz & R.S. Poulsen spec. nov. (Fig. 12)   
MycoBank: MB 822685  
 Diagnosis: A species of Henssenia characterized by a placodioid thallus, 0.4–1.2(–1.6) cm diam., with marginal lobes 0.4–0.8(–1) mm wide and ascospores that are (7–)9–12 × 4–6 μm.   
 Type:—CROZET. Île de La Possession, Mont Branca, versant sud-est, c. 300 m, 46°26’18”S, 51°50’08”E, fell-field, sur un petit rocher, 21 November 2015, D. Ertz 20556 (holotype BR!).   
 Etymology: The specific epithet refers to the morphological similarity with H. glaucella.   
 Thallus placodioid, 0.4–1.2(–1.6) cm diam., margin distinctly and ±regularly lobate, central parts crustose-areolate; marginal lobes 0.4–0.8(–1) mm wide; areoles of central parts flat, c. 0.2–0.8(–1) mm diam. Upper surface smooth in distal parts, rarely slightly roughened in central parts, pale brown with a pale greyish margin, not pruinose, without soredia or isidia. Apothecia discrete or sometimes 2 contiguous, up to 0.6 mm diam., immersed when young, bursting through the cortex, remaining immersed or becoming sessile, usually not, or only slightly, constricted at the base at maturity; disc dark brown or reddish-brown to almost black, plane to slightly convex at maturity; thalline margin narrow at maturity, up to 0.1 mm wide, concolourous with thallus. Thalline anatomy: thallus c. 90–130 μm thick; upper ±algal-free layer consists of a c. 10–30 μm thick, hyaline layer of ±isodiametric (4–8 μm diam.) or slightly elongated (5–17 × 2–7 μm diam.) cells; necrotic layer on the surface inconspicuous or c. 2 μm thick. Photobiont cells 5–9 × 7–11 μm, often slightly wider than long, heterocytes c. 5–7 × 10–11 μm diam.; hyphae below algal layer more loosely arranged, mainly ±horizontally aligned; hyphae in medulla c. 3–5 μm wide. Lower surface with a ±irregularly developed cortical layer c. 5–10 μm thick, composed of thick-walled, ±isodiametric cells, 2–3 μm diam. Apothecial anatomy: Proper exciple laterally 40–80 μm, with elongated cells c. 4–10 × 3–4 μm becoming isodiametric, thick-walled, c. 4–8 μm diam. near the surface, basally indistinguishable from the hypothecium. Hymenium 60–125 μm high; epihymenium brown, c. 5–10 μm; paraphyses 2.5–3 μm wide; apical cells swollen, with brown walls, up to 4–5 μm wide. Hypothecium inversely cone-shaped, extending down to substratum, very thick, 125–175 μm high, consisting of densely short-celled hyphae above, becoming paraplectenchymatous with cells 3–5(–6) μm diam. below. Asci 63–75 × 10–12 μm; ascospores 8 per ascus, simple or 1-septate (plasma-bridge), ellipsoid to narrowly ellipsoid with rounded ends, (7–)9–12 × 4–6 μm. Pycnidia not seen.   
 Distribution and ecology: Henssenia subglaucella is known from Crozet and Kerguelen. The investigated collections of this species are found on exposed rocks from low to high elevations. It is easily overlooked due to its small size.   
 Notes: The species is phylogenetically and microscopically very close to H. glaucella but differs mainly by the smaller size of the thallus having always a brownish tinge. Specimens 92, 446b, 460, 20817 have a lichenicolous fungi (tiny black perithecia) restricted to the hymenial disc and appearing to be specific and frequent on H. subglaucella.   
 Additional examined specimens: CROZET. Île de La Possession, between Mt. Branca and Base Alfred-Faure, c. 250 m, 46°26’0”S, 51°51’0”E, 10 December 1998, R. S. Poulsen 92 (C); Arête des Djinns, c. 700–900 m, 46°26’07”S, 51°46’48”E, 6 December 2015, D. Ertz 20817 (BR); Mont du Mischief, tout près du sommet, c. 910 m, 46°24’59”S, 51°41’37”E, 08 December 2015, D. Ertz 20866 (BR). KERGUELEN. Péninsule Courbet, Mt. du Chateau, c. 0.5 km NE of Les Créneaux, 640 m, 49°14’6”S, 70°08’0”E, 20 December 1998, R. S. Poulsen 446b, 460 (C).
description: Published as part of Ertz, Damien, Poulsen, Roar S., Charrier, Maryvonne & Søchting, Ulrik, 2017, Taxonomy and phylogeny of the genus Steinera (Arctomiales, Arctomiaceae) in the subantarctic islands of Crozet and Kerguelen, pp. 201-238 in Phytotaxa 324 (3) on pages 227-229, DOI: 10.11646/phytotaxa.324.3.1, http://zenodo.org/record/13698300