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COSEWIC assessment and status report on the Boreal Felt Lichen in Canada
- Assessment Summary
- Executive Summary
- COSEWIC Mandate, Membership and Definitions
- List of Figures
- Species Information
- Population Numbers, Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Acknowledgements, Literature Cited, and The Authors
COSEWIC Status Report
Boreal Felt Lichen
It is not clear whether the generic name of the lichen was derived from the hairiness of the upper cortex or from the eriostratum of the underside (erion being the Greek name for wool and derma that for skin). Both features are highly characteristic of the genus.
In general, Erioderma is one of the most primitive genera of foliose lichens that may have originated in the Southern Hemisphere, on the Supercontinent of Gondwana (Jørgensen, 1990). It may have arrived in Laurentia (present day North America) on the microcontinent of West Avalonia, which had previously been in contact with the north-west coast of South America during the late Ordovician (Caradoc-Ashgile, 450-440 mya, see Figure 6, Benedetto et al., 1999). Its arrival in the British Isles is likely as a result of the previous contact of the microcontinent of East Avalonia with the Colombian Coast during the Late Ordovician (Arenigian, 490-480 mya, see Figure 5 in Benedetto et al. 1999). This hypothesis of the origin of the genus in the Southern Hemisphere is based on the hybrid chemistry of the lichen depsidone eriodermin (Connolly et al., 1984; Figure 2) found in Erioderma pedicellatum and several closely related species in South America and South Africa (Maass, 2003b). To confirm the hybrid nature of this species, it would be logical to search for and identify suitable fertile species that would have been able to donate the A and B rings present in eriodermin. These include species that contain either argopsin or pannarin or both as potential donors for ring A, i.e., E. groendahlianum (= E. polycarpum), E. leylandii ssp. azoricum, E. leylandii ssp. leylandii, E. leylandii ssp. velligerum (=E. chilense) and E. meiocarpum. Through the loss of genes in producing the β-orcinol substituents (via C-methylation or C-formylation), any of the above species could have generated a mutant producing the orcinol depsidone conwrightiin instead of the original β-orcinol depsidone. This mutant would have been a most suitable ring B donor for the metabolite eriodermin in hybrids formed through back-crossing with any of the above mentioned original species. The postulated mutant is one of the ancestors of today’s E. wrightii. The latter species contains one orcinol depside, i.e., wrightiin (Maass and Hanson, 1986) and one insufficiently characterized orcinol depsidone that accompanies the depside as a minor constituent and has therefore been named conwrightiin (Maass, unpublished). This minor constituent, characterized by its mass spectrum (in preparations extracted from lichens collected in Jamaica) was also encountered by Elix et al. (1986) in E. wrightii collected in Ecuador. Even the morphology of E. wrightii, with its concave apothecial disks (which appear to be present also in E. leylandii, according to the doctoral thesis by Ahlner 1948) makes the ancestor of this species a good candidate for having donated the genes for making the orcinol type of ring B in eriodermin.
Boreal felt lichen (Figure 1) is a foliose lichen that is usually between 2-5 cm in diameter but can attain a diameter of up to 12 cm. Smaller thalli have a relatively small holdfast area that is loosely attached to the substrate, most often to the mats of the hepatic Frullania tamarisci ssp. asagrayana rather than to the naked bark itself. On larger thalli, some of the radiating lobes are able to develop their own holdfasts. This may result in subdivision of the thallus.
The hairiness on the upper cortex of the lichen is clearly visible and is a characteristic feature of all species of Erioderma. The upturned margins reveal the whitish underside that is devoid of a lower cortex.
The thallus lobes are slightly involute, (i.e., curled upwards along their margins) exposing their whitish undersides. These appear felted by bundles of pale to darkish gray to bluish-gray branched hapteres (often discoloured) that form a dense eriostratum under optimal conditions. The hapteres have a dual function in anchoring the thallus to its substrate and taking up the nutrients from either stemflow or branchflow, whenever it rains. In the hydrated state the thallus has a bluish gray appearance due to the cyanobacterium, Scytonema. In the dry state its colour is dark gray to grayish brown.
The hairs on the upper surface of the thallus are commonly poorly developed but may be quite prominent in some specimens. In the generic key for the distinction between Erioderma, Leioderma and Parmeliella these hairs are described as being stiff and prominent (Galloway and Jørgensen 1987). Those in E. pedicellatum are often moderately branched, even in the centre of the thallus. Along the edges of the thallus they can form a semi-arachnoidal tomentum, whereas on older thalli this feature may be missing.
In cross-section, the lichen thallus is distinctly stratified. The upper cortex of the thallus consists of 2-4 layers of very thick-walled irregular colourless cells (30-50μ thick), with funnel-shaped gaps found to almost penetrate the cortical layer. The function of these intercellular spaces may be to promote the gas exchange required for photosynthesis and nitrogen fixation. Immediately below a narrow darkish transition zone of less than one cell layer thickness, the curled chains of the large-celled photobiont Scytonema are recognized. The algal layer is only between 45-90μ thick, in comparison with the well developed medulla in which the thickness varies between 200-600μ. A morphologically distinct lower cortex is absent. Thin-walled and branched septate rhizines can reach 1.5 mm in length.
Each thallus, after having reached at least 1.0 cm in diameter, develops an abundance of short-stalked apothecia up to 1.5 mm in diameter when reaching maturity. Mature thalli are usually at least 2-5 cm, and in rare cases, up to about 10 cm or more in diameter. Upon reaching this stage, young apothecia, whose margins are often fringed with whitish hairs, may be spotted along the growing edges of the thallus. More mature and varying developmental stages of apothecia will eventually be found scattered all over the upper surface, with up to nearly 100 per thallus. Whilst the apothecial stalk may be slightly compressed, the hymenial surfaces of the apothecia are initially flat but become conspicuously globose when mature. They are then dark brown and between 0.5-1.5 mm in diameter. Vegetative propagules in the form of either soredia or isidia are conspicuously absent in the life cycle.
Boreal felt lichen is distinguished chemically by the presence of a chlorinated depsidone called eriodermin (Figure 2; Maass, 1980). This constituent was first isolated in pure form from specimens of E. sorediatum D.J. Gall. & P.M. Jørg. (which is the sorediate counterpart of the fertile tropical species E. physcioides Vain). Eriodermin is an aromatic aldehyde in which the aldehyde group is in ortho position to a phenolic hydroxyl group, accounting for the PD+ (orange) reaction. Most other conventional colour test reagents give negative results (K-, C-, KC, I-).
Figure 2: The Chemical Structure of the Mixed Depsidone Eriodermin (which is the only secondary metabolite in Erioderma pedicellatum and related species of South and Central America, the Caribbean and/or Southeastern Africa)
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