Publication Cover - Number 1 May 2000.

Lichens Growing on Northern Red Oak (Quercus rubra) Trees in the Northeast

Roger Monthey (USDA Forest Service, Durham, NH)
Constance Stubbs (Botany Professor, University of Maine-Orono)

Many woodland owners in the Northeast have northern red oaks growing on their property. Have you ever wondered what those strangely colored and mysteriously shaped vegetative growths on the trunks of the oaks are? According to Dr. Constance Stubbs, Department of Biological Sciences at the University of Maine-Orono, these growths are lichens and they are an important component of forest ecosystem function and diversity. Dr. Stubbs surveyed the lichens growing on red oak in the University of Maine Experimental Forest, during a study of the associations between lichens and small invertebrates such as water bears, nematodes, and mites. She published the results of this study in 1989 in The Bryologist (Volume 92, No. 4). Dr. Stubbs listed 15 species of foliose (leafy growth form) and fruticose (shrubby or hairlike growth form) lichens. We added the common names of these lichens (where available) as taken from the 1994 publication The Lichens of British Columbia by Trevor Goward, Bruce McCune, and Del Meidinger. In the brief descriptions below, we borrowed liberally from Mason Hale’s book How to Know the Lichens published in 1979.

Dr. Stubbs’ list includes the following species: Allocetraria oakesiana, Bryoria furcellata, Cladonia sp., Evernia mesomorpha, Flavoparmelia caperata, Hypogymnia physodes (monk’s hood), Melanelia subaurifera (abraded brown), Myelochroa galbina, Parmelia squarrosa (salted shield), Parmelia sulcata (powdered shield), Parmeliopsis ambigua (green starburst), Phaeophyscia rubropulchra (shadow lichen), Punctelia rudecta (speckleback lichen), Ramalina dilacerata, and Usnea subfloridana. This publication provides photographs and brief descriptions of some of these species.


Allocetraria oakesiana (listed asTuckermannopsis oakesiana by Stubbs and Cetraria oakesiana by Mason Hale)

This is a yellowish-green lichen similar to Flavoparmelia caperata (see below); however, the lobes of this lichen are narrower (0.1–3 mm wide) than in Flavoparmelia caperata and are usually strap-shaped and linear. The soredia (vegetative propagules) are also mostly on the margins of the lobes. The species is apparently common on the bark of hardwoods and conifers and on rocks in northern woods.

Allocetraria oakesiana.

Bryoria furcellata

This lichen is hairlike in appearance and its thallus (vegetative body of the lichen) is a beautiful chestnut brown. Fully mature specimens have soredia erupting from white surface soralia (regions in which soredia are produced). It is rather stiff, tufted to prostrate, and measures 4–10 cm long. According to Mason Hale, it is by far the most common Bryoria lichen in the Eastern States.

Photo: Bryoria furcellata

Evernia mesomorpha

This lichen is shrubby in appearance. It is pale yellowish-green, limp, erect to pendulous, and about 4–6 cm long. The surface of the thallus is irregularly wrinkled and has granular soredia. It is considered common in northern forests.

Photo: Evernia mesomorpha

Flavoparmelia caperata

This is a yellow-green lichen that can cover large areas he tree trunk. The lobes of its thallus are quite broad and apically rotund (3–10 mm wide).

Photo: Flavoparmelia caperata

Hypogymnia physodes

This is a hollow lichen. The thallus is light mineral gray. If you cut the lobes with a sharp object, the thallus is hollow. This lichen has soredia on the inner surface of its burst lobe tips. It is very common on both hardwoods and conifers.

Photo: Hypogymnia physodes

Parmelia squarrosa and Parmelia sulcata

Dr. Stubbs found these species the most prevalent lichens growing on red oak trees. These Parmeloid (shieldlike) lichens are identified by the whitish or pale grayish blue color on the upper surface of the thallus and the presence of rhizines (rootlike hairs that attach the thallus to its substrate) on the blackish lower surface. The difference between the two species is technical. The thallus of P. squarrosa has isidia (tiny, fingerlike asexual reproductive structures that protrude from the upper thallus) which are not associated with soralia (regions in which soredia are produced). The thallus of P. sulcata is sorediate and the soredia are confined to discrete soralia.

Parmelia squarossa
Photo: Parmelia sulcata

Parmeliopsis ambigua

This lichen is often found at the base of deciduous and conifer trees and on bare wood, stumps, and logs. The lobes are narrow (1 mm wide). The thallus is light greenish-yellow with extensive areas of soredia on the upper surface. The thallus adheres closely to the bark.

Photo: Parmeliopsis ambigua

Phaeophyscia rubropulchra

When you scrape this lichen with a sharp object (such as a razorblade, but your fingernail will do), the interior of the thallus (the medulla) will show a reddish color. This makes this lichen fairly easy to identify. The upper surface is brownish and the thallus lobes are usually linear or elongate.

Photo: Phaeophyscia rubropulchra

Punctelia rudecta

This is a pored lichen—its thallus has white pores (pseudocyphellae) on its upper surface. The upper surface of the thallus is greenish mineral gray and the lower surface is tan or pale brown, which distinguishes it from Parmelia squarrosa and Parmelia sulcata. It has rhizines on its lower surface.

Photo: Punctelia rudecta

Ramalina dilacerata

This is a shrubby lichen. Its thallus is greenish-yellow, tufted, and the branches are irregularly flattened with perforations toward the base. Its branches are partially inflated and hollow (use a hand lens). It has disk-shaped apothecia (sexual reproductive structures).

Photo: ramalina dilacerata

Usnea subfloridana

This is another lichen that is shrubby in appearance. The thallus is greenish-yellow, stiffly tufted, and sorediate. The base of the thallus is constricted and blackish. It is considered by Hale to be very common on trees in open woods.

Photo: Usnea subfloriadana

Published by:
USDA Forest Service
State and Private Forestry
Northeastern Area
P0 Box 640
Durham, NH 03824

Photo Credits:
Cover background photo: Bill Leak, USDA Forest Service
Cover inset photos: Ken Dudzik, USDA Forest Service

Photo 1: Steve Sharnoff
Photo 2: Steve Sharnoff
Photo 3: Ken Dudzik
Photo 4: Ken Dudzik
Photo 5: Ken Dudzik
Photo 6: Steve Sharnoff
Photo 7: Steve Sharnoff
Photo 8: Steve Sharnoff
Photo 9: Dick Homola, former Emeritus Professor of Botany at the University of Maine
Photo 10: Steve Sharnoff
Photo 11: Steve Sharnoff
Photo 12: Steve Sharnoff  

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.  

Contact Roger Monthey, for more information about this document.