|DIVERSITY OF LIFE|
LICHENS ARE CHIMERICAL ENTITIES AND, THEREFORE, HAVE NO NATURAL LINES OF DESCENT
Lichens (LI-kins) is formed from a Greek root that means lick (leicho -λείχω). The reference may be to their use as medicinals. At that time, lichens included some mosses, liverworts, as well as lichens.
INTRODUCTION TO THE LICHENS
By convention, the lichens are classified as members of the Kingdom Fungi. However, because the fungus (the mycobiont) and the alga (the phycobiont) can live separately in a free-living state, both components should have separate taxonomic designations. The difficulty is compounded by the lichen itself. The symbiotic chimeroid structure called the lichen truly is a different organism from either of its fungal or algal components thus it should have its own "taxonomic" designation, one based on form rather than phylogeny. I have adopted the convention of the fungal classification, but we include a description of the Form-Phylum Lichens in recognition of the uniqueness of the particular symbiosis. Certainly, lichens as a taxon follow the dictum of deux veritas.
A. Peltigera, a foliose lichen.
B. Cladonia, a fruticose lichen.
C. Parmelia, a foliose lichen.
D. Usnea, a fruticose lichen.
E. Pyrenula, a crustose lichen.
F. Calicium, the spike lichen.
G. Opegrapha, a crustose lichen.
|Images taken from:
SYNOPTIC DESCRIPTION OF THE LICHENS
|The following description comes from Margulis and Schwartz (1988), Hale (1979), Ahmadjian (1967), and Nash (1996).|
I. SYNONYMS: lichens
II. NUMBERS: >18,000 species.
III. PHYLUM CHARACTERISTICS:
A. ASEXUAL REPRODUCTION:The lichen can reproduce itself by the production of diaspores, lichenized structures in which the algal and fungal units function together as subunits of the lichen thallus; diaspores may be fragments of the thallus or specialized structures such as soredia and isidia.
ARTIFICIAL HIERARCHICAL CLASSIFICATION OF THE LICHENS.
|The taxonomy of this "phylum" is artificial since both the alga and fungus also can exist as separate entities. The form-phylum has 3 form-classes (based on the type of mycobiont: Ascomycota, Basidiomycota, or Deuteromycota) and 8 form-orders. The taxonomy is roughly based on that of Margulis and Schwartz (1988).|
Fruiting bodies are perithecia.
Fruiting bodies are mazaedia, an ascocarp in which the asci degenerate at maturity and the ascospores are liberated free in the hymenium.
Pseudothecia poorly differentiated, asci irregularly distributed.
Pseudothecia well delimited, resembling perithecia, asci more or less regularly arranged in the stromatic layer.
Pseudothecia well delimited, round and resembling apothecia, lirelliform, or irregular in outline.
Ahmadjian, V. 1967. The Lichen Symbiosis. Blaisdell Publishing Co. Waltham, Mass. 152 p.
Hale, M. E. 1979. How to Know the Lichens. 2nd ed. Wm.C. Brown Publishers. Dubuque, IA.
Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York.
Nash, T. H., III, ed. 1996. Lichen Biology. Cambridge University Press. New York. 303 pp.
By Jack R. Holt. Last revised: 03/10/2013