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Lichens Pan-Z (2007) - Flora of New Zealand Lichens - Revised Second Edition Pan-Z
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Rhizocarpon Ramond ex DC.

RHIZOCARPON Ramond ex DC., 1805

Type : Rhizocarpon geographicum (L.) DC. [=Lichen geographicus L.]

Description : Flora (1985: 503).

Key

1
Thallus white, grey or brownish; rhizocarpic acid absent
2
Thallus yellow, yellow-green or greenish; rhizocarpic acid present
18
2
Ascospores with only transverse septa
3
Ascospores muriform
8
3
Ascospores 1-septate, hyaline or pigmented
4
Ascospores 3-septate, 16–28 μm long
submodestum
4
Medulla I−; epithecium K−
5
Medulla I+ blue; epithecium K+ purple; thallus K+ yellow (stictic acid) or K−, C−; ascospores hyaline becoming brown, 16.5–22 × 8–10 μm
polycarpum
5
Thallus K−; ascospores hyaline becoming brown, 20–24 × 8.5–10 μm
6
Thallus K+ red (norstictic acid) or rarely K+ yellow (stictic acid); ascospores dark bluish green, 20.5–22 × 9–12 μm
copelandii
6
Thallus orange, oxydated with deposition of Fe; apothecia sessile, contorted; exciple carbonised [Campbell I.]
oxydatum
Thallus grey; apothecia plane, ±innate; exciple not carbonised [South I.]
hochstetteri
7
Asci 1- or 2-spored
8
Asci 8-spored
9
8
Asci 1-spored
disporum
Asci 2-spored
geminatum
9
Ascospores soon becoming dark green-blue or brown
10
Ascospores remaining hyaline, occasionally becoming brown with age
13
10
Thallus K+ red and/or C+ red
11
Thallus K− or + yellow (stictic acid); exciple K−; ascospores mostly 3-septate and hyaline but some dark blue-green ascospores usually present
postumum
11
Thallus K+ red (norstictic acid), C−
12
Thallus K− or ±yellow, C+ red (gyrophoric acid)
grande
12
Medulla I−; hymenium purple; epithecium blue-black; ascospores submuriform, 21–34 × 12–14 μm
purpurescens
Medulla I+ blue; epithecium red-brown to brown-black; ascospores muriform, 19–34(42) × 10(12–16)–18 μm
eupetraeum
13
Medulla I−; exciple and epithecium K+ purple or K−
14
Medulla I+ blue; exciple and epithecium K+ violet-red
distinctum
14
Exciple K−; ascospores submuriform to muriform, remaining hyaline; medulla K+ yellow, Pd+ orange (stictic acid)
15
Exciple K+ purple; ascospores with only 1 (or 2) longtudinal septa, often becoming blue-black at maturity
subpostumum
15
Ascospores 30–50 μm long
16
Ascospores < 30 μm long
reductum
16
On calcareous rocks; thallus white; stictic acid usually present (K+ yellow, Pd+ yellow); apothecia innate, margins usually pruinose; ascospores 30–35 μm long
petraeum
On acidic rocks; thallus grey-brown; no lichen compounds present (K−, Pd−); apothecia large, ≥ 1.5 mm diam., margins swollen, epruinose; ascospores 33.5–50 μm long
lavatum
17
Ascospores submuriform or muriform
18
Ascospores 1-septate, small, 9–18 × 4–6 μm
21
18
Medulla I+ distinctly blue; epithecium brown or green, K+ purple-red or −; not parasitic on other lichens
19
Medulla I− or faint-blue; epithecium brownish black, K+ purple-red; parasitic on species of Aspicilia
* viridiatrum
19
Apothecia not surrounded by crescent-shaped areolae; thallus K−, Pd+ yellow (psoromic acid)
20
Apothecia surrounded by crescent-shaped areolae; thallus K+ yellow, Pd+ orange (stictic acid)
lecanorinum
20
Thallus bright greenish yellow; ascospores with 6–24 cells in optical section
geographicum ssp. geographicum
Thallus whitish yellow to whitish; ascospores with 6–8 cells in optical section
geograhicum ssp. arcticum
21
Thallus small, 0.3–1 cm diam.; K−, Pd+ yellow (psoromic acid); parasitic on Sporastatia testudinea
* pusillum
Thallus 2–10 cm diam.; K+ red, Pd+ orange (norstictic acid) or K+ yellow, Pd+ orange (stictic acid); not parasitic on other lichens
superficiale

Rhizocarpon is a large genus of some 200 mainly widespread species (Kirk et al. 2001; Ihlen 2004a; Feuerer & Timdal 2004), occurring in temperate, often alpine and/or polar habitats. It is included in the family Rhizocarpaceae, together with the genera Catolechia, Epilichen and Poeltinula (Hafellner 1984; Eriksson et al. 2004; Pennycook & Galloway 2004; Eriksson 2005). The Rhizocarpaceae is characterised by a lecideine exciple; asci with a distinct amyloid cap in the distal part of the tholus; and branched and anastomosing hamathecial filaments (Hafellner 1984; Ihlen & Ekman 2002).

Species of Rhizocarpon colonise predominantly siliceous rocks, although some species occur on basicolous substrata and a number of taxa are parasitic on other lichens (Poelt & Hafellner 1982; Poelt & Vězda 1984; Holtan-Hartwig & Timdal 1987; Poelt 1990). The literature of Rhizocarpon is extensive, covering mainly Northern Hemisphere and arctic taxa (Vainio 1922, 1944, 1949; Lynge 1932, 1936; Lamb 1940; Runemark 1956a, 1956b; Thomson 1968a; 1979, 1997; Honegger 1978b; Geyer et al. 1984; Poelt 1988; Timdal & Holtan-Hartwig 1988; Feuerer 1991; Asta & Letrouit-Galinou 1995; Fryday 1996, 2000a, 2000b, 2004a; Clayden 1997a, 1997b, 1998; Elvebakk & Hertel 1997; Ihlen 2004a; Feuerer & Timdal 2004), with to date very little recent work done or attempted on Southern Hemisphere populations. Antarctic taxa are discussed by Dodge (1948: 114–119; 1973: 89–95) and Øvstedal & Lewis Smith (2001).

A recent molecular study of 13 species of Rhizocarpon (nine of which occur in New Zealand) suggested that the genus as presently circumscribed is polyphyletic and that several morphological characters (i.e. ascospore septation; ascospore pigmentation; amyloid reaction of the medulla, presence of rhizocarpic acid, and presence of stictic acid metabolites), formerly used to subdivide Rhizocarpon into subgeneric groupings (e.g. Thomson 1968a; Feuerer 1991), showed that these characters had all changed several times and that consequently their utility in predicting relationships within the genus is artificial and of limited value (Ihlen & Ekman 2002).

Rhizocarpon is much in need of careful collection and revision in New Zealand. The present account discusses 22 taxa. The taxon R. candidum C.W.Dodge (Dodge 1948: 114; Galloway 1985a: 504) is referable to Pertusaria.

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