Peltigera didactyla
≡Lichen didactylus With., Bot. Arr. Veg. Gr. Brit. 1 (2): 718 (1776).
Description : Thallus orbicular, small, often cochleate. 0.5–2(–3) cm diam. Lobes 1–2 (rarely 3–5) cm long, 0.5–1(–2) cm wide, plane to ascending, 100–200 μm thick. Margins entire, often incurled. Upper surface coriaceous, dark slate blue-black, suffused dark red-brown when wet, brownish grey or pale greyish green, suffused red-brown when dry, tomentose; tomentum most apparent in sterile, sorediate lobes, thinly arachnoid, continuous or discontinuous in scattered, rather tattered patches at margins and centrally; sorediate. Soralia marginal and laminal in rounded to oblong, erose spots or patches, disappearing in older, usually fertile specimens; soredia coarse, granular, grey-blue to red-brown. Lower surface pale whitish or brownish pink. Veins distinct, raised, 0.5–1.0 mm wide, whitish to pale-buff, darkening centrally, interstitial spaces conspicuous, white, fibrous. Rhizines simple at first, soon becoming fasciculate, ±penicillate at maturity, to 2.5 mm long, rather sparse at margins, common at centre. Apothecia on ascending, revolute lobes, 2–4 mm diam., rounded to irregular-elongate, disc red-brown to brown-black, matt, epruinose, margins pale-buff, crenulate–corrugate. Ascospores elongate–fusiform, 5–7-septate, 55–70 × 3–4 μm.
Chemistry : Medulla TLC−, all reactions negative; soredia C± pink-red (fading rapidly) containing gyrophoric acid [corresponding to the chemodeme P. didactyla var. extenuata (Nyl. ex Vain.) Goffinet & Hastings ffinet & Hastings 1994, 1995)].
N: South Auckland (Kawhia, Napier–Taupo Road). S: Nelson (St Arnaud Ra., Travers Ra., Reefton), Canterbury (Lake Tekapo, Mt Sebastopol, Rangitata River mouth), Otago (Matukituki Valley, Pigeon I. Lake Wakatipu, Dunstan Mts, Mt Benger, Gem Lake, Lake Onslow, Deep Stream, Taieri Mouth), Southland (Argyle Burn, Oreti Plains, Doubtful Sound, Greenhills) [map in Galloway (2000d: 12, fig. 3)]. On damp, often bare soil or among mosses, or in subalpine turf, commonly at roadside verges among moss and pebbles at edge of bitumen, or at edges of gravel paths or in weedy, mossy banks in gardens, s.l. to 1500 m. It is normally a rather ephemeral, short-lived, fast-growing, pioneer species in disturbed habitats (e.g clay banks, washouts and slips, alongside roads), commonly attacked by lichenicolous fungi such as the orange-pink Illosporium carneum, and by Corticifraga fuckelii and C. peltigerae (Hawksworth & Santesson 1990; Vitikainen 1994b). In my garden in Central Otago, the species actively colonised S-facing banks at the base of species of Helleborus, attaining a diameter of 1–3 cm in a period of 6 months with growth being most rapid in the winter. At this time too it is often visually striking in moss along roadsides when the pinkish galls of Illosporium carneum become noticeable. A widespread, cosmopolitan lichen known from North America, Great Britain, Scandinavia, Greenland, Svalbard, Europe, Asia, South America, Africa, Australia, South Georgia, South Orkney Is, South Sheltland Is, and Antarctica (Swinscow & Krog 1988; Nimis 1993; Santesson 1993; Vitikainen 1994b, 2004a; Esslinger & Egan 1995; Hansen 1995; Elvebakk & Hertel 1997; Brodo et al. 2001; Øvstedal & Lewis Smith 2001; Coppins 2002b; McCarthy 2003c, 2006; Nimis & Martellos 2003; Santesson et al. 2004; Søchting et al. 2004).
Cosmopolitan
Illustrations : Moberg & Holmåsen (1982: 178); Wirth (1987: 341; 1995a: 683); Vitt et al. (1988: 231); Goffinet & Hastings (1994: 20, fig. 29); Goward et al. (1994b: 98, fig. 10B); Vitikainen (1994b: 38, fig. 81); Hansen (1995: 49); Johnson et al. (1995: 348); McCune & Geiser (1997: 208); Dobson (2000: 283; 2005: 316); Brodo et al. (2001: 7, pl. 5; 508, pl. 594) ; Øvstedal & Lewis Smith (2001: pl. 59).
Peltigera didactyla is characterised by: the terricolous/muscicolous habit; the presence of laminal, orbicular soralia (frequently reacting C+ pink), and a ±tomentose upper surface on small, cochleate lobes that are also often attacked by white to orange or pinkish lichenicolous fungi. The juvenile, sorediate phase is eventually superseded by a fertile, non-sorediate phase. It is distinguished from P. ulcerata by the thinner, ±tomentose lobes.
Specimens from high-alpine habitats (e.g. Dunstan Mountains) have very thick, ±upright lobes and develop a thick, white, fibrous tomentum at the margins (often ±loosely attached and sloughing off), and copious white, penicillate rhizines below; the laminal soralia are often poorly developed. A particularly robust form from Doubtful Sound, Fiordland [Murray 3946 and identified by James Murray as P. canina var. canina (Murray 1960c: 396)] has broad, ±rounded lobes (1–2 cm broad and 3–5 cm long) that are uniformly tomentose and with ±scabrid–areolate patches at margins and occasionally centrally. It has scattered submarginal (rarely central) soralia, containing coarse, granular, blue-grey soredia (C+ pink), and characteristic flocculent–entangled, short rhizines associated with narrow, raised veins on the lower surface, the rhizines often projecting as a fringe at lobe margins. The Fiordland and high-alpine specimens, although much larger than the typical, small, cochleate forms from disturbed habitats in rural and urban areas, are here maintained in P. didactyla pending further study of the variation of this species in New Zealand. Molecular studies on the P. didactyla complex were recently published (Goffinet et al. 2003).
