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Lichen Resources


Lichen Collections and Facilities

Lichen Collection of the U.S. National Herbarium

The lichen collection of the U.S. National Herbarium, Smithsonian Institution, with approximately 250,000 specimens, is the largest lichen collection in North America and one of the ten largest collections in the world. The collection is especially rich in type material with an estimated 2,500 type specimens currently registered. The emphasis of the collection is North American lichens, especially the Parmeliaceae, which was studied by Mason E. Hale, Jr., and the Cladoniaceae, which was studied by Paula DePriest. Most acquisitions over the past 40 years reflect Dr. Hale's personal collections, which numbered over 80,000. Although the majority of his collections are North American, they also include African, Australian, Latin American and Antarctic materials. The collection also includes valuable historical materials from Evans, Arséne, Merrill, Willey, and Dodge, and many modern exsiccati as well. The U.S. National Herbarium has incorporated lichen collections from the USDA National Fungus Collections and the Missouri Botanical Garden.

Research Materials and Libraries

In addition to the specimens, the lichen collection contains associated research materials, including microscope slides, chemical extracts, chemical identification plates, SEM photographs and negatives from Mason E. Hale and frozen lichen tissues, DNA samples, and a small number of living cultures from Paula DePriest. An associated literature collection includes Hale's research notes, collecting notebooks, photographs and kodachrome slides; an extensive modern reprint collection; and a large library of lichen literature. The library includes the Stevenson collection of rare and historic literature, as well as a number of contemporary books. The library is supplemented by the Department of Botany Branch Library, which subscribes to all major lichenological serials and purchases major lichenological works.

Databases and Products of Lichen Research Projects

[Note: The link to these databases will open a new browser window. To return to this page, close the new window.]

Parmeliaceae: Searchable List of Names in the Parmelioid Genera

Names and Synonymy in the Cladoniaceae

Search for Lichens in the online collections search

Bouly de Lesdain's Lichens du Mexique Types Collected by Arsène G. J. Brouard (Frère G. Arsène)

DePriest, P. T. Arsène's Collections at the U.S. National Herbarium Pertinent to Bouly de Lesdain's Lichens du Mexique. Cryptogamie, Bryologia-Lichénologia 17: 87-102. 1996.
     At least 104 isotypes and isosyntypes of Mexican lichens described by Bouly de Lesdain in Lichens du Mexique are accessioned in the U.S. National Herbarium. These specimens, most obtained in 1918 as a gift from Arsène G. J. Brouard (Frère G. Arsène), are duplicates of type materials destroyed in 1940 with Bouly de Lesdain's private herbarium. Since few of these original materials are extant in other collections, the U.S. National Herbarium's set of isotypes and isosyntypes provides potential lectotypes and neotypes for many names published in Lichens du Mexique.

Checklist of the Lichenized Fungi of the Guianas, by H.J.M. Sipman

Key to the Lichen Genera of the Guianas, by H.J.M. Sipman

Key to the Cladoniaceae of the Guianas, by T. Ahti and H.J.M. Sipman

Monographic Studies in the Cladoniaceae - Lichen-forming Ascomycetes
Department of Botany
U.S. National Museum of Natural History
Smithsonian Institution


PEET Project Abstract

Names and Synonymy in the Cladoniaceae

PEET III (2000) Abstracts and Report

Project Personnel

Paula T. DePriest (Principal Investigator, Smithsonian Institution)

Samuel Hammer (Co-Principal Investigator, Boston University)

Rytas Vilgalys (Co-Principal Investigator, Duke University)

Teuvo Ahti

Soili Stenroos

Rebecca Yahr

A Project of the National Science Foundation's (NSF) Partnerships for Enhancing Expertise in Taxonomy program. The work is supported by the U.S. National Science Foundation's PEET Program, an Andrew W. Mellon Fellowship and the Smithsonian Institution Scholarly Studies fund.
Photos of PEET Participants

What is a Lichen?

Lichens are the symbiotic association of a fungus and an alga.

Most lichen-forming fungi are members of the ascomycetes, the fungal group that includes the destructive bread molds, the edible morels, and the commercially-important baking and brewing yeast. A few are members of the basidiomycetes, which also include the typical mushrooms.

The algae may be either members of the chlorophyta, which includes the green algae such as most plankton, or the cyanobacteria, the blue-green algae that often form pond scum. The algae may be either single cells or filaments, chains of cells. Some lichens have more than one type of alga.

What is symbiosis?

Symbiosis, by one definition, is the interaction between two or more species that benefits at least one of them.

For lichens, we think that both the fungus and the alga benefit from the association. As a simple model, lichens are like gardens. The alga is similar to a plant that under optimal conditions produces simple sugars from atmospheric carbon dioxide and water by photosynthesis. The fungus, as the "gardener," tends the alga, providing shelter and protection from the extremes of the environment. As a consequence the alga produces enough additional sugars to supply the fungus with nourishment. With some of these sugars, the fungus makes organic compounds that possibly protect both partners from herbivores—a type of natural pesticide.

Where do lichens grow?

Lichens are remarkable for their ability to grow in extreme environments. Lichens are found in the hottest desert, the coldest tundra, and the wettest rain forest. Some lichens are able to tolerate salt spray on coastal cliffs and periodic inundation by fast-moving streams; however, no lichen is truly aquatic. Lichens grow on soil, woody debris, rocks, tree bark, tree leaves, and on other lichens.

What are the lichen growth forms?

In combination, the lichen symbionts produce a growth form that is unlike either fungi or algae growing alone. The association produces an undifferentiated "plant" called a thallus. Three growth forms are easy to recognize:

Example of a crustose lichen.Crustose: crust-like, adhering tightly to the substrate by their entire lower surface. Some endolithic lichens are embedded in their rock substrate.

Example of a foliose lichen.Foliose: leaf-like with a distinct upper and lower surface, attached to their substrate only by small root-like structures, rhizines.

Example of a fruticose lichen.Fruticose: shrub-like, pendulous strands or hollow stalks called podetia, usually attached to the substrate at the base or holdfast.

How do lichens reproduce?

The lichen-forming fungi may reproduce sexually or asexually.

Sexual reproduction in ascomycetous lichens is typically by production of fruiting bodies called apothecia that produce the sexual propagules (ascospores).

Asexual reproduction is by fragmentation of the thallus or by special structures: soredia (tufts of a few algal cells wrapped in hyphae), isidia (cylindrical, finger-like projections from the upper surface) or lobules (miniature lobes developing along the margins).

How are lichen species identified?

Thallus characters: growth form, size, shape of the thallus; color of cortex; rhizines and cilia of the lower cortex and margin, pores and cracks of the upper cortex.

Reproductive characters: presence of vegetative propagules; shape and color of the apothecia (if present); shape, number of cells, size, color of the ascospores.

Chemical characters: production of lichen compounds.

Ecological characters: distribution, elevation, habitat, substrate.

Algal host: the type of alga, either chlorophyta or cyanobacteria.


Paula DePriest
Department of Botany
National Museum of Natural History
Smithsonian Institution, Washington, DC

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