A
SYSTEMATICS OF
TROPICAL CRUSTOSE LICHENS
A

[Latest update: October 31st, 2000]

robert3.jpg (19692 Byte)

With several hundred species, Graphidaceae are the dominant group of crustose lichens in the tropics.
Most representatives grow in the forest canopy or in open situations.
(Photograph by Robert Lücking)

[Numbers in brackets relate to relevant publications; underlined phrases without links indicate pages under construction].

 

Lichens are well-known and most conspicuous in cool, humid climates. It is therefore often concluded that cool-temperate zones shelter the highest lichen diversity on earth. In the tropics, lichens are largely undercollected, even in areas where higher plants are well investigated. In spite of that, a high number of names is available for tropical lichens, dating mainly from the last and the beginning of the present century when, due to scarce collections and the lack of understanding of specific variability, almost every specimen was described as new. Although the poor taxonomic background prevents from reliable estimates of lichen diversity, recent studies indicate that species richness in tropical regions may surpass that of temperate areas. It is now thought that countries such as Costa Rica, Colombia, Ecuador or Papua New Guinea shelter the highest lichen diversity in the world, with 2000-2500 species [ARVIDSSON, Rep. Bot. Inst. Univ. Aarhus 15: 13-19 (1986); SIPMAN in CHURCHILL et al., Biodiversity and Conservation of Neotropical Montane Forests: 313-320 (1995); APTROOT, Bibl. Lichenol. 68: 203-213 (1997); 21].

Crustose lichens account for most of the diversity in tropical areas [SIPMAN & HARRIS in LIETH & WERGER, Tropical Rain Forest Ecosystems: 303-309 (1989)], particularly in the rain forest, and it is especially this group where our taxonomic knowledge is far from satisfying and which is often neglected in floristic or community surveys. While some groups of crustose lichens have an exaggerated number of species described and are in great need of revision, others are hardly even recognized in their diversity. In order to document lichen diversity in tropical rain forests and to understand their importance for the ecosystem, it is therefore indispensable to revise their taxonomy and systematics with traditional and modern methods. Thus far, only few compilations exist which give access to tropical crustose lichens, of which the following deserve special attention: Awashti's "A key to the microlichens of India, Nepal and Sri Lanka [AWASHTI, Bibl. Lichenol. 40: 1-337 (1991)], and Sipman's "Identification key to the genera of lichenized fungi (lichens) in the Neotropics" [SIPMAN, Internet version, regularly updated].

Based on our research on foliicolous lichens, in 1995 various projects dealing with the systematics of tropical crustose lichens were started. The main focus is laid on the order Ostropales and the lichen families Asterothyriaceae and Gomphillaceae [33, 40]. Using morphological and molecular data, the phylogeny and systematics of both families will be revised, supported by a grant of the German Research Society (DFG). This project is carried out in co-operation with Aino Henssen (Marburg), François Lutzoni (Chicago, U.S.A.), Emmanuël Sérusiaux (Liège, Belgium), Goran Thor (Stockholm, Sweden) and Antonín Vezda (Brno, Czech Republic). Further projects deal with the systematics and taxonomy of particular genera, as for example Porina, Aspidothelium and Phyllobathelium [34, 60].

robert4a.jpg (14461 Byte)

robert4b.jpg (11356 Byte)

The lichen genera Asterothyrium (A. rotuliforme) and Psorotheciopsis (P. guajalitensis) are greatly confused in the literature
and of particular interest in our systematic studies on tropical crustose lichens.
(Photographs by Robert Lücking)

In addition, since 1996 several monographs for the series Flora Neotropica are under preparation. They include the above mentioned families and further groups, in total seven entities:

robert5.jpg (16508 Byte)