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Ascospore germination, thallus initiation, and areole and prothallus development in the lichen Rhizocarpon lecanorinum Anders were examined using light, fluorescence and scanning electron microscopy. The ascospore germ hyphae remain very short and do not form a prothallus-like mycelium. Instead, a compact soredium-like granule develops directly from sporeling contact with a compatible species of Trebouxia. Diffuse initial stages involving non-trebouxioid algae are lacking. The onset of thallus differentiation is marked by the deposition of rhizocarpic acid in an incipient cortical layer within the apical part of the granule. As pigmentation and cortexformation transform this structure into a typical areole, radiating prothallus hyphae are simultaneously initiated from its basal margin. Most areoles formed subsequently in the marginal prothallus lack subtending melanized hyphae and apparently stem from overgrowth by the prothallus of photobiont cells on, or in, the substratum. Apothecia reach maturity in thalli as small as 2 mm in diameter. It is proposed that the lack of diffuse hyphal growth in sporelings and telescoped morphogenesis of R. lecanorinum are part of a life history strategy geared to precocious, heavy investment in ascospore production. The R. lecanorinum-Trebouxia symbiosis has a number of features which make it well-suited for further studies of the life history and development of prothallus-forming crustose lichens with sexually reproducing mycobionts.

The genus Rinodina (Physciaceae), with approximately 300 species, has been subject to few phylogenetic studies. Consequently taxonomic hypotheses in Rinodina are largely reliant on phenotypic data, while hypotheses incorporating DNA dependent methods remain to be tested. Here we investigate Rinodina degeliana/R. subparieta and the Rinodina mniaraea group, which previously have not been subjected to comprehensive molecular and phenotypic studies. We conducted detailed morphological, anatomical, chemical, molecular phylogenetic and species delimitation studies including 24 newly sequenced specimens. We propose that Rinodina degeliana and R. subparieta are conspecific and that chemical morphs within the R. mniaraea group should be recognized as distinct species. We also propose the placement of the recently described genus Oxnerella in Physciaceae.

The plant communities of shallow soil and bare rock on outcrops of rhyolite and basalt are described for the area south of Lake Abitibi, Quebec. Analysis of data from 34 sample plots by means of reciprocal averaging ordination indicates that most of the intersite variation in composition and structure is due to succession. The two rock types have distinctive assemblages of epilithic lichens and bryophytes but their thin soil communities do not differ significantly. Soil coverage and depth are controlled in part by bedrock slope and microtopography and increase uniformly in relation to the postfire age of the outcrop tree stands. The ground layer macrolichens and bryophytes undergo a succession of dominant species and growth forms, but the open-crown coniferous stands show little evidence of self-regeneration through tree seedling establishment or vegetative propagation. Stands of different age dominated by Pinus banksiana and by Picea mariana do not form a clear successional sequence. Fire recurrence prevents complete closure of the outcrop tree canopy.

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Metal-enriched habitats often harbor physiologically distinct biotas able to tolerate and accumulate toxic metals. Plants and lichens that accumulate metals have served as effective indicators of ecosystem pollution. Whereas the diversity of metal-tolerant lichens has been well documented globally, the literature of metal-tolerant lichen communities for eastern North America is limited. We examined the lichen flora of the Callahan Mine, a Cu-, Pb-, and Zn-enriched superfund site in Brooksville, Hancock County, Maine, U.S.A. Through collections along transects across metal-contaminated areas of the mine, we documented 76 species of lichens and related fungi. Fifty species were saxicolous, 26 were terricolous. Forty-three species were macrolichens, 31 were microlichens. Although no globally rare or declining species were encountered at the mine, two regionally rare or declining species, Stereocaulon tomentosum and Leptogium imbricatum, were found. The species found at the Callahan Mine were mostly ecological generalists frequenting disturbed habitats. Two extensively studied Cu-tolerant lichens, Acarospora smaragdula and Lecanora polytropa, and other known Cd-, Cu-, Pb-, and Zn-tolerant taxa, were found at the site. Rhodora [Vol. 113

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