Introduction
Placocarpus Trevis. emend. O. Breuss contains two species, P. schaereri (Fr.) Breuss, the type species of the genus, and P. kashiwadanii Aptroot & K.H. Moon (Breuss Reference Breuss1985; Moon & Aptroot Reference Moon and Aptroot2009). Placocarpus schaereri is a juvenile parasite on Protoparmeliopsis muralis (Schreb.) M. Choisy (syn. Lecanora muralis (Schreb.) Rabenh.) usually on calcareous substrata, as well as possibly parasitic on Lobothallia radiosa (Hoffm.) Hafellner based on our observations and also on other lichens (fide Zhurbenko Reference Zhurbenko2008). It eventually develops a thick independent areolate thallus which can become effigurate (see Wirth Reference Wirth1995 and Ozenda & Clauzade Reference Ozenda and Clauzade1970 for excellent images).
Placocarpus schaereri is a wide-spread species with its distribution centred on the Mediterranean. It occurs in Europe, North Africa, the Middle East (Zschacke Reference Zschacke1933–1934; Ozenda & Clauzade Reference Ozenda and Clauzade1970; Zehetleitner Reference Zehetleitner1978) and extends north into Ukraine (Kondratyuk et al. Reference Kondratyuk, Navrotskaya, Khodosovtsev and Solonina1996) and Russia (Zhurbenko Reference Zhurbenko2008). It is noticeably missing from Great Britain, Fennoscandia and Greenland. Placocarpus schaereri was reported from the United States by Thomson (Reference Thomson1989) but Breuss found the specimen to be a species new to science and described it as Placopyrenium coloradoense Breuss (Breuss Reference Breuss2009).
After much confusion concerning the circumscription of the heterogeneous genus Placocarpus Trevis., Breuss emended Placocarpus to accommodate Dermatocarpon monstrosum (Schaer.) Vain., whose older name was Parmelia schaereri Fr. (Breuss, Reference Breuss1985), while the other species included by Trevisan in Placocarpus were transferred to Catapyrenium, Heteroplacidium, Placidiopsis and Verrucaria. The diagnostic characters of the genus, based on P. schaereri, are juvenile parasitism, a rimose areolate to placodioid thallus up to 2·5 mm thick with stipitate to semi-stipitate areoles, paraplectenchymatous cortex, prosoplectenchymatous I+ (blue)medulla inspersed with small colourless crystals, simple and halonate ascospores, and pycnidia of the Dermatocarpon-type (Breuss Reference Breuss1985; Gueidan et al., Reference Gueidan, Savić, Thüs, Roux, Keller, Tibell, Prieto, Heiðmarsson, Breuss and Orange2009). The genus was monotypic and well-supported by molecular analysis (Gueidan et al., Reference Gueidan, Roux and Lutzoni2007) until Aptroot and Moon (Reference Moon and Aptroot2009) described P. kashiwadanii from Korea. This was reported to be non-parasitic on other lichens and to have a thick thallus with well-developed effiguration, but some important characters were not mentioned in the protologue, and molecular data were not available.The genus Placocarpus is a sister genus to Verrucula (Gueidan et al. Reference Gueidan, Roux and Lutzoni2007), which contains only species parasitic on Caloplaca species with anthroquinones and on Xanthoria elegans (Navarro-Rosinés et al. Reference Navarro-Rosinés, Roux and Gueidan2007).
In this paper we describe a new species, Placocarpus americanus K. Knudsen, Breuss & Kocourk., a juvenile parasite on Protoparmeliopsis muralis on Conejo Volcanics that develops an independent thallus of dispersed stipitate to sub-stipitate areoles and emends some of the characters used to define the genus.
Materials and Methods
Specimens were hand-sectioned and preparations mounted in water and 10% solution of potassium hydroxide (KOH) and examined using standard microscopy. Amyloid reactions were tested with Lugol's iodine (Merck 9261) (I) pre-treated or not with 10% solution of potassium hydroxide (I/K). Measurements were made on material mounted in water. Macrophotographs were taken with a digital Olympus C5050 camera on an Olympus SZX 9 Stereomicroscope.
Specimens of P. schaereri studied: Czech Republic: Central Bohemia: Distr. Beroun, Křivoklátsko Protected Landscape Area, Točník, below Točník castle, MTB: 6149 A08, 370 m, on Protoparmeliopsis muralis on porphyritic rocks, 6 vii 1999, J. Kocourková (PRM 900181); Praha, Dalejské udolí valley, near Aretusinová rokle quarry, MTB 5952, 310 m, on P. muralis, 23 i 1993, J. Horáková (PRM 758588); České středohoří PLA, Distr. Louny, Třtěno, NM Třtěnské stráně, N of village, S-facing slopes, 50°25′47.069″N 13°52′32.714″E, 220 m, on P. muralis var. muralis, on marl soil, on quartzite boulder, 12 × 2008, J. Kocourková (PRM 915108). Southern Moravia: PLA Pálava, Dist. Břeclav, NR Děvín, below the Dívčí hrad ruin, MTB 7165, 370 m, on P. muralis on calcareous rock, 10 × 2000, J. Kocourková (PRM 760746).—Spain: Catalonia: Cataluna, Cadi Mountain, at top of cliff before entrance to the village, 1400 m, 28 v 2003, C. Gueidan s.n. (UCR).—Slovakia: Malé Karpaty Mountains, Smolenice village, on calcareous rocks on Molpír hill, 300 m, 29 × 1991, J. Liška (PRM 887625).— Turkey: Sinas Gùnùn 38°39.306′N 37°18.169′E, 1506 m, 9 vii 2008, M. Halici s.n. (hb. Halici).
The Species
Placocarpus americanus K. Knudsen, Breuss & Kocourk. sp. nov
Mycobank: MB 513217
Similis Placocarpo schaereri a quo differt ascosporis minoribus (18–22 × 5–8 μm), areolis dispersis,minoribus (0·3–1·0 mm diametro, usque ad 0·5 mm crassis) medullaque non crystallis minutis inspersa, I−.
Type: USA, California, Ventura Co., Santa Monica Mountains, Westlake Village, Conejo Open Space, near Lake Elenor Dam, slope above Highway 23 South, 34°08′ 12″ N 118° 51′ 07″ W, 291 m, on Protoparmeliopsis muralis on Conejo Volcanics in wall of drainage channel, 24 November 2008, Knudsen 10711, J. Kocourková & T. Sagar (LI—holotypus; PRM, UCR—isotypi).
(Fig. 1)
Placocarpus americanus, habitus. Scale=1 mm.
Thallus crustose of dispersed individual areoles, >0·5 mm thick and 0·2–1·0 mm wide, areoles apparently undivided, loosely attached by weakly- to well-developed stipes. Upper cortex thin, 3–5 layers thick, paraplectenchymatous, cells 5–8 μm diam., hyaline, the upper layers becoming melanized and overlain with a fine epinecral layer; upper surface greyish-white. Algal layer discontinuous, algal cells chlorococcoid, 8–10 μm diam. Medulla continuous with attaching hyphae, prosoplectenchymatous, 100–200 μm thick, hyphae hyaline, 2 μm wide, cells to 10 μm long or septa indistinct, lacking an inspersion of small crystals, I−.
Perithecia globose, 100–200 μm diam., immersed in the thallus, with darkened ostiole region, lacking an involucrellum; exciple hyaline, 10–15 μm thick. Hamathecium of periphyses; periphyses hyaline, branching or not, 15–25 × 0·5–1·0 μm long, septate or septa indistinct, cells mostly 5 μm long. Asci 45–50 × 15–18 μm, contents I+ red. Ascospores simple, hyaline 18–22 × 5–8 μm, halonate only when immature, irregularly bi-seriate.
Pycnidia not observed.
Etymology. The species is named after the continent where it was discovered and because of its wide separation from the well-documented distribution area of P. schaereri in Africa, Asia and Europe, centred on the Mediterranean.
Substratum and ecology. On Protoparmeliopsis muralis on Conejo Volcanics, becoming independent, in microhabitats with high relative humidity in the the immediate area, such as on a north slope in shade with winter seepage and on a wall of a seasonal drainage channel on a slope.
Distribution. Currently known only from Southern California, Santa Monica Mountains, Ventura County, on Conejo Volcanics, at elevations between approximately 250–300 metres. However, the host is widespread in western America in a variety of habitats, and it is possible that additional records of P. americanus will be found.
Discussion
The infection of the host begins in the same way in P. americanus as in P. schaereri. At first the host shows no signs of the infection by Placocarpus except for perithecia forming in the thallus and apothecia of the host. At the second stage the thallus of the host begins to discolour as Placocarpus forms a new cortex. Progressively an independent thallus is formed until individual units of the Placocarpus are identifiable.
Placocarpus americanus differs from P. schaereri in five characters: it does not form a thick continuous thallus (0·5–1·0 mm thick vs. up to 2·5 mm thick) and has dispersed areoles (not forming a thallus with a rimose-areolate centre and sometimes effigurate edge), its ascospores are shorter and narrower than those of P. schaereri (18–22 × 5–8 vs. 17–30 × 8–9 μm) and halonate only when immature, its medulla is I− and lacks an inspersion of small crystals. Placocarpus americanus shares with P. schaereri sub-umblicate areoles with stipitate or sub-stipitate structures, a paraplectenchymatous cortex, a prosoplectenchymatous medulla, and they also share the same main host as juvenile parasites. Placing P. americanus in Placocarpus emends the genus so that the possession of a thick, placodioid thallus, an I+ inspersed medulla, and halonate ascospores, are now variable within the genus. Thus Verrucula differs from Placocarpus in having a pseudocortex rather than a paraplectenchymatous cortex, is restricted to different hosts, occurring on Caloplaca species and Xanthoria elegans, and has good molecular support as a genus (Gueidan et al. Reference Gueidan, Roux and Lutzoni2007; Navarro-Rosinés et al. Reference Navarro-Rosinés, Roux and Gueidan2007; Gueidan et al. Reference Gueidan, Savić, Thüs, Roux, Keller, Tibell, Prieto, Heiðmarsson, Breuss and Orange2009).
Placocarpus americanus differs from P. kashiwadanii in having larger ascospores (18–22 × 5–8 vs. 14–16 × 6–8 μm) and by having a dispersed thallus vs. a thick effigurate thallus, as well as being a juvenile parasite. Because the two sister genera, Placocarpus and Verrucula, contain only parasitic species, the placement of P. kashiwadanii in the parasitic genus Placocarpus is suspect, unless P. kashiwadanii is a juvenile parasite on lichens and the authors had observed only mature, independent thalli. As with several other species placed in Placocarpus Trevis. in the past before it was emended by Breuss (Reference Breuss1985), Moon and Aptroot (Reference Moon and Aptroot2009) recognize that P. kashiwadanii may eventually be transferred to another genus, but their description lacks important information such as cortex and medulla structure, the reaction of the medulla to I, and pycnidia type although abundant conidia were produced.
Other specimen examined. USA: California: Ventura Co., Santa Monica Mountains, Agoura Hills, south of Agoura Road, 34°08′ 37″ N 118° 46′ 00″, 267 m, early stage of infection, on Protoparmeliopsis muralis on moist shaded rock outcrop with Dudleya species, 2008, Lendemer 11461 & K. Knudsen (NY, UCR).
We thank Cécile Gueidan, M. Gökhan Halici, Lauren Sparrius and M. P. Zhurbenko for their help in supplying specimens or literature,Tarja Sagar, NPS bryologist, for guiding us through the Santa Monica Mountains, John Tiszler (NPS) for his support of our research in so many ways throughout the years and J. Giles Waines, director of the UCR Herbarium. The work of J. Kocourková was supported by a grant from the Ministry of Culture of the Czech Republic (MK00002327201). The work of Kerry Knudsen was supported by an Academic Fellowship from the Santa Monica Mountains Fund for the continuing study of the lichen biota of the Santa Monica Mountains.
