Henssenia Ertz, R.S. Poulsen & Søchting, 2017

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, Phytotaxa 324 (3), pp. 201-238 : 223-224

Henssenia Ertz, R.S. Poulsen & Søchting gen. nov.

MycoBank: MB 822683

Diagnosis: A genus of Koerberiaceae characterized by a subfoliose to placodioid rosette-shaped thallus up to 3.5 cm in diam., with distinct marginal lobes up to 2 mm wide, an upper ±algal-free layer consisting of a ±paraplectenchymatous layer, a scytonemoid photobiont with filaments or clusters typically arranged in vertically elongated fascicles between the fan-shaped ascending hyphae, simple, small ascospores sometimes having a plasma-bridge.

Type: Henssenia glaucella (Tuck.) Ertz, R.S. Poulsen & Søchting

Etymology: The new genus is dedicated to the German lichenologist Aino Henssen (1925-2011) for her important contribution to the taxonomy of cyanolichens.

Thallus subfoliose to placodioid, closely appressed to the substrate, rosette-shaped, up to 3.5 cm diam., margin distinctly and ±regularly lobate, central parts sometimes becoming ±crustose-areolate; marginal lobes separated by deep fissures, radiating, ±flabellate, up to 1.5(–2) mm wide. Upper surface smooth or with striae in distal parts, often becoming weakly roughened in central areas, not pruinose, without isidia. Areoles derived from secondary rimose cracking between the main fissures, complete or incomplete, angular, flat to slightly convex. Lower surface smooth, usually without rhizohyphae. Prothallus not developed. Apothecia often abundant, discrete or sometimes contiguous, usually laminal and mostly restricted to the central areas of the thallus, developed on the upper surface of the thallus, up to 1 mm diam., immersed when young, eventually more or less level with the surface of the thallus or sessile; disc dull brown, reddish-brown or black, not pruinose; thalline margin visible in species having sessile ascomata, narrow, smooth, concolourous with thallus. Thalline anatomy: thallus thin; hyphae in upper 1/3–3/4 of thallus running perpendicularly to surface and densely packed, getting short-celled towards upper surface; upper ±algal-free layer (or ‘cortex’) consists of a hyaline, ±paraplectenchymatous layer, which is overlaid by a very thin, uneven, amorphous, semi-translucent necrotic layer. Photobiont a species of filamentous cyanobacteria, with cells often wider than long, lacking a thick gelatinous sheath (?), ‘scytonemoid’, mainly present in the upper half of the thallus with the exception of the thin upper ‘cortical’ layer, heterocytes paler, filaments or clusters typically arranged in vertically elongated fascicles between the fan-shaped ascending hyphae, being usually pale orange in the upper layer and greenish in deeper parts of the thallus; hyphae below the algal layer more loosely arranged, either vertically aligned as in the central areoles, or ±horizontally radiating towards the apices of the marginal lobes, generally interspersed with simple chains of algal cells; hyphae in ‘medulla’ c. 2–5 μm wide. Lower surface pale brown to whitish in distal parts, with a ±paraplectenchymatous and irregularly developed thin cortical layer, sometimes with a few short hyphae attaching the thallus to the substrate. Apothecial anatomy: Proper exciple thin or almost inconspicuous, hyaline, sometimes pale brownish near the surface, composed laterally of hyphae arranged in parallel with elongated cells, basally becoming paraplectenchymatous; thalline exciple visible in non-immersed ascomata, thin, concolourous with the thallus. Hymenium hyaline, not inspersed, I+ blue turning dark reddish brown, KI+ deep blue; epihymenium brown, I+ blue turning dark reddish brown, KI+ blue; paraphyses sparingly branched, mainly in upper part of hymenium; apical cells swollen. Hypothecium hyaline, consisting of densely short-celled hyphae above, becoming paraplectenchymatous below, I+ pale orange, KI+ pale orange with few dark blue spots. Asci narrowly clavate, usually with a ±distinct foot, with a ±well-developed tholus, with the outermost layer becoming distinctly I+ reddish, KI+ dark blue (rest of the wall I–, KI–); ascospores (4–7)–8 per ascus, simple or with a more or less median plasma-bridge but without a true transverse septum, ellipsoid or subglobose, small, up to 15 × 7 μm, without a gelatinous sheath, I– (except internal cytoplasm becoming dark orange). Pycnidia rarely present, immersed in the thallus, Umbilicaria type; conidia simple, bacilliform.

Chemistry: No lichen substances detected by TLC.

Notes: Henssenia differs from Steinera mainly by the simple ascospores sometimes having a plasma bridge and in this case the ascospores appear as being 1-septate. The genus also differs from Steinera s. str. by usually smaller thalli, a ‘scytonemoid’ photobiont, asci with a thinner upper apical wall, and a different ascomata ontogeny (cf. Henssen & James 1982, p. 231, studied for ‘ Steinera ’ radiata ). Henssenia might be related to Peltularia (a genus for which no sequences are available so far) because of similarities in anatomy and developmental morphology of the ascocarp ( Henssen & James 1982), but the type species of this genus differs notably by an umbilicate and more heteromerous thallus (e.g. Henssen & James 1982, Jørgensen & Galloway 1984).

The new genus Henssenia is part of the Koerberiaceae . Members of this family share as synapomorphy the presence of radiating lines caused by radiating-photobiont bundles just beneath the upper cortex separated by bundles of cyanobiont-free medullary hyphae (Spribille & Muggia 2014). In Henssenia the thin striae are clearly visible on the thallus surface in H. werthii , but are less apparent in the other species.