Placynthium nigrum
Common name
Blackthread lichen
Synonyms
Lichen niger Huds.
Family
Placynthiaceae
Flora category
Lichen – Native
Endemic taxon
No
Endemic genus
No
Endemic family
No
Structural class
Lichens - Squamulose
Current conservation status
2018 | Not Threatened | Qualifiers: SO
Brief description
Characterised by the calcicolous habit (limestone and calcareous sandstone), the closely attached black rosette-shaped, squamulose to subcrustose thallus surrounded by a conspicuous, blue-black prothallus; ±central apothecia to 1 mm diam., with a black or brown-black disc with a thin, entire, concolorous margin; and 1–3-septate ascospores, 7–18 × 3.5–7 μm.
Distribution
North Island: Northland (Waipu Caves), South Auckland (North of Waikaretu). South Island: Nelson (Kaihoka Lakes, Mt Arthur), Westland (Punakaiki, Dolomite Point, Pancake Rocks), Marlborough (Chalk Range, Kaikoura Peninsula), Canterbury (Nape Nape, Weka Pass, Flock Hill, Castle Hill, Lowry Peaks Range, Motunau Beach, Mt Somers, Ashburton Gorge), Otago (Oamaru, Hampden, Northern Cemetery Dunedin, Otago Peninsula), Southland (Queen’s Park Invercargill, Forest Hill, Castle Rock near Dipton, Clifden).
A widespread, circumpolar species in the Northern Hemisphere.
Habitat
On limestone and a range of calcareous building materials such as cement, mortar and concrete, especially on bridge parapets, and walls made of limestone, and on tombstones and memorials in cemeteries.
Detailed description
Thallus in rosettes, olive to blackish, to 3 cm diam., not effigurate, surrounded by a black, marginal prothallus. Lobes squamulose, flat, 0.4-1.5 mm wide, margins crenate or digitate, squamules scattered at thallus margin, crowded centrally, forming a continuous crust which may become areolate, areolae 1-4 mm wide and 1-3 mm tall. Isidia present or absent, cylindrical, 0.2-0.5 × 0.05-0.1 mm. Lower surface blue-green, rhizinate. Apothecia 1 mm diam., with dark proper margin, disc brown or black, concave at first becoming plane or convex. Ascospores narrow-ellipsoid, 1- to 3-septate, 7-18 × 3.5-7 µm.
Chemistry: TLC−, all reactions negative.
Substrate
Saxicolous, calcareous building materials (cement, mortar, concrete, tombstones)
Etymology
nigrum: Latin meaning black
Attribution
Fact sheet prepared by Marley Ford (26 December 2022). Brief description, Distribution, Habitat, and Features sections copied from Galloway (1985) & Galloway (2007).
References and further reading
Galloway D.J. 1985: Flora of New Zealand: Lichens. Wellington: PD Hasselberg, Government Printer. 662 pp.
Galloway D.J. 2007: Flora of New Zealand: Lichens, including lichen-forming and lichenicolous fungi. 2nd edition. Lincoln, Manaaki Whenua Press. 2261 pp.