Monday, February 7, 2011

Dog Lichen Out Muscles the Grass

Dog Lichen, Peltigera canina
Lichens are excellent primary collonisers. All they need is sunlight, something to anchor to and, given enough moisture, they will grow. Most species are to seen on bare rock, on the bark of trees or the peaty soils of moors. Here their main competitors for light resources are bryophytes which rarely outgrow them. There are some exceptions, however, a notable one being the Dog Lichen, Peltigera canina. While it can be found on walls and rocks and other dry habitats, this marcolichen with Nostoc cyanobacteria as its photobiont (1), is most commonly seen in Ireland growing among grasses in woods and lawns (2). The large lobed thalli can form patches 10 cm across, which helps when competing with grasses for resources. Furthermore, the lichen has been shown to produce compounds with inhibitory effects on the germination of grass seeds and the subsequent growth of seedlings (3). The presence of cyanobacteria as the photobiont also gives P. canina the competitive advantage of being able to fix its own nitrogen (4).
Thalli of the Dog Lichen, Peltigera canina
The thalli of P. canina are thick and downy and when wet are dull brown, but pale grey when dry and produce distinctive reddish brown spore producing structures on the edge of the lobes (2) (the sample pictured was observed in January). The underside is covered with well developed rhizinae.
Fruiting Structures of the Dog Lichen, Peltigera canina
The ability of P. canina to survive in a number of habitats lies in the fact that its is not a single species but a species complex (5). Twenty five taxa are known in the complex, however only seventeen of these are recognised, the other eight being under-described.
Rhizinae of the Dog Lichen, Peltigera canina
  1. Miadlikowska and Lutzoni 2000, International Journal of Plant Science 161 pp. 925–958
  2. Phillips 1980, Grasses, Ferns, Mosses and Lichens of Great Britain and Ireland p. 176
  3. Pyatt 1967, The Bryologist 70 pp. 326-329
  4. Lockhart et al. 1978, FEMS Microbiology Letters 3 pp. 127–130
  5. Miadlikowska et al. 2003, Mycologia 95 pp. 1181–1203

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