SPECIES FACT SHEET
Common Name: Burnet’s skin lichen
Scientific Name: Leptogium burnetiae C.W. Dodge
Kingdom: Fungi
Division: Ascomycota
Class: Lecanoromycetes
Order: Peltigerales
Family: Collemataceae
Nomenclature
The nomenclature of this species has changed several times, leading to some confusion. C. W.
Dodge named L. burnetiae in 1964. Sierk (1964) named North American specimens Leptogium
hirsutum. In 1973, Jørgensen combined L. hirsutum into a variety of L. burnetiae writing, "L.
hirsutum is so closely related to it and best treated as a variety of it [sic]." In 1997 he included
only L. burnetiae (not L. burnetiae var. hirsutum) in a key to the hairy Leptogium species of the
world, evidently deciding there was no discernable difference between the variety and the
species in the strict sense.
Technical Description:
Thallus foliose, gelatinous when wet, medium-sized, 3-10 cm diameter, loosely adnate. Lobes 315 mm wide, with rounded margins. Lower surface pale to medium gray, smooth, with dense
white (rarely pale brown) tomentum of long cylindrical hairs. Upper surface medium gray to
bluish gray when dry, without definite wrinkles or ridges, matte to somewhat shiny, with or
without small white hairs. Isidia originate as single, separate papillae on lobe surface, somewhat
in from margin, then become cylindrical, simple to branched to dense and coralloid; also
common in a single row along margins. Isidia matte and similar in color to thallus or slightly
darker. Soredia absent. Medulla formed of densely packed hyphae, mostly lying parallel to the
cortex and forming an almost solid hyphal mass in the center of the medulla. On the top and
bottom of this mass, cyanobacteria are packed so tightly that their chains are not readily visible;
instead they are visible as single cells (Stone 2010). Apothecia rare, laminal, stalked, 0.5-2.5
mm wide. Spores colorless, with crosswalls and longitudinal walls (muriform), 30-45 x 12-18
µm. Photobiont cyanobacterial (Nostoc).
Chemistry:
Spot test reactions negative. No secondary metabolites have been detected. (Brodo et al. 2001;
Nash et al. 2004).
Other descriptions and illustrations:
Hinds and Hinds 2007, Jørgensen 1997, Nash et al. 2004, Stone 2010.
Distinctive Characters:
All Leptogium species are gelatinous lichens that swell and become jelly-like when wet. They
are unstratified; the photobiont does not form a distinct layer within the thallus but is intermixed
with fungal hyphae. Unlike Collema species, they do have an upper and lower cellular cortex,
appearing as a surface layer of square to shortly rectangular cells. These features can best be seen
with a compound microscope (see below).
(1) blue-gray, foliose, gelatinous lichen with a densely white-hairy lower surface, (2) isidia that
originate as single bumps on the surface, become cylindrical and then branched to coralloid with
age, (3) medulla with tightly packed hyphae mostly parallel to and some perpendicular to the
cortices.
Similar Species
Leptogium saturninum is most similar to L. burnetiae and can be very difficult to distinguish.
In L. saturninum, surface coloration and texture appear to be connected. Isidia begin as a pattern
of dark coloration near the edge of a lobe. The pattern originates as an even speckling of dark
spots on the surface. As the thallus grows and widens this even dusting of dark particles becomes
divided into patches, leaving bare, light-colored tracks through somewhat angular patches of
dark-colored fine particles. With age, these dark areas begin to become rough and isidia erupt
out of the thallus surface, destroying the cortex and forming patches of granular isidia which then
become dense dark piles of granular isidia. (Stone 2010).
In L. burnetiae, isidia originate as single, separate papillae on lobe surface, somewhat in from
margin, then become cylindrical, simple to branched to dense and coralloid; also common in a
single row along margins. Isidia similar in color to thallus or slightly darker.
The structure of the medulla, seen in cross section, is also a distinguishing character.
To clearly see the difference in medulla type, extremely thin sections are essential. If the
sections are too thick, multiple layers of hyphae obscure the medullar structure.
In L. saturninum, the medulla is formed of hyphae Perpendicular to and parallel to the upper and
lower cortices, separated by spaces so the whole medulla looks airy and open. Within this open
framework, chains of cyanobacteria lie in curves. Thalli of L. saturninum are variable in
thickness from 100 to 300 µm, but the same structure is found in all. The amount of space
between hyphae does vary from nearly touching to quite widely spaced, but the typical medulla
is quite open-looking.
In contrast, the medulla of L. burnetiae is formed of densely packed hyphae, mostly lying
parallel to the cortex and forming an almost solid mass of fungal strands in the center of the
medulla. Above and below this mass, cyanobacteria are packed so tightly that their chains are not
readily visible; instead they are visible as single cells. Thalli of L. burnetiae seem quite variable
in overall thickness and thickness of the central hyphal strand mass, but the pattern of a dense
central-medullar mass with dense algae above and below remains consistent.
Leptogium pseudofurfuraceum has a white-tomentose lower surface and cylindrical isidia.
However, unlike L. burnetiae, it has a finely wrinkled upper surface, and a reddish-brown to
brown-gray color. The dark brown to black, shiny isidia have a distinct dimple at the tip.
Collema species are also dark-colored gelatinous lichens, but they lack an upper and lower
cortex. This can be observed with a wet mount of a cross-section of the thallus through a
compound microscope; see illustrations on page 15 in Brodo et al. (2001). In addition, Collema
species are rarely hairy.
Leptochidium albociliatum may have a white-hairy lower surface, but can be distinguished by
short, stiff, clear, marginal hairs that are usually abundant and conspicuous with a hand lens.
Fact Sheet for Leptogium burnetiae
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Life History:
L. burnetiae is often sterile, producing apothecia only occasionally. However, it reproduces
asexually through abundant isidia, which are usually present year-round. Isidia are heavy
propagules, therefore dispersal is limited.
Range, Distribution, and Abundance:
Globally, this species is widespread in the montane tropics, extending into warm temperate
regions of Asia, Africa, Europe and North America (Nash et al. 2004).
In the Pacific Northwest, it occurs in Washington, British Columbia and Alaska. It has been
verified from only one location in Washington: in the Columbia River Gorge National Scenic
Area (Björk 10428). Two specimens similar to L. burnetiae but with different structure of the
medulla have been found in Oregon. One is at Saddle Mountain State Park (Derr 883) and the
other in Jackson County on Crowfoot Creek (Medford District BLM, Callagan 1054).
Habitat:
This species is found on tree bark and on mossy rocks. In the Columbia River Gorge it occurs on
Quercus garryana bark in a ponderosa pine/ garry oak/ arrowleaf balsamroot plant association at
low elevations (100 and 400 feet). In Alaska, it is known from the Tongass National Forest at
low-elevation sites (≤ 250 feet), where it occurs on Alnus sinuata, Picea sitchensis, Salix sp., and
Populus trichocarpa (U.S. Department of Agriculture (no date).
Threats:
For this cyanolichen, shade and air moisture are an important part of the habitat, so any change
in forest density or shading could degrade the habitat. The primary threat to this species is forest
management activities that remove host trees or change the moisture regime. Timber harvest
projects that remove or damage oaks, cottonwoods, and other hardwoods, especially in riparian
areas, may directly threaten populations or reduce habitat (D. Stone, personal observation).
Conservation considerations:
Protect the known site and the two possible sites. Known populations can be protected by
restricting removal of host trees and nearby habitat, preserving the light and moisture regime.
Search riparian areas on Federal lands for more populations. Continue to protect riparian
corridors, with large enough buffers to maintain humidity regimes.
Conservation rankings: Global: G3G5. National: not ranked. ORBIC: S1. WNHP: not ranked.
Preparers: Erika Wittmann & Jeanne Ponzetti
Date completed: 9/18/2006
Revised: Daphne Stone 2012, February 2012
References
Brodo, I., Sylvia Sharnoff, and Stephen Sharnoff. 2001. Lichens of North America. New
Haven, CT: Yale University Press. 795 pp.
Fact Sheet for Leptogium burnetiae
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Goward, T., B. McCune, and D. Meidinger. 1994. The Lichens of British Columbia: Illustrated
Keys. Part 1 – Foliose and Squamulose Species. Special Report Series 8, British Columbia
Ministry of Forests Research Program. Victoria, B.C.: Crown Publications. 181 pp.
Hinds, J. W. and P. L. Hinds. 2007. The Macrolichens of New England. New York Botanical
Garden Press, NY.
Jørgensen, P.M. 1997. Further notes on hairy Leptogium species. Symb. Bot. Ups. 32: 1.
McCune, B and L. Geiser. 2009. Macrolichens of the Pacific Northwest.
Corvallis, OR: Oregon State University Press. 386 p.
Nash, T.H.III, B.D. Ryan, P. Diederich, C. Gries, F. Bungartz, editors. 2004. Lichen flora of the
greater Sonoran Desert region: volume II. Tempe, AZ: Lichens Unlimited & Arizona State
University. 742 p.
Sierk, H.A. 1964. The genus Leptogium in North America north of Mexico. The Bryologist
67(3): 245-317.
Stone, D. 2010. A Search for Leptogium burnetiae C. W. Dodge in the Pacific Northwest.
Interagency Special Status/Sensitive Species Program website,
http://www.fs.fed.us/r6/sfpnw/issssp/ Last visited 21 Feb 2012.
USDA Forest Service. no date. National Lichens and Air Quality Database and Clearinghouse.
http://gis.nacse.org/lichenair/index.php?page=query&type=plot Last visited 24 February 2012.
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Fig. 1. Thin cross-sections of Leptogium burnetiae, showing a medulla formed of tightly packed
hyphae many of which are parallel to the cortices, with little or no space between hyphae.
Cyanobacteria are mostly above and below the central mass of hyphae, and packed so tightly that
whole chains are not visible. Bar is 10 µm. (Stone 2010)
Fig. 2. Lobe edges in Leptogium burnetiae, showing smooth pale edges and isidia forming from
single bumps on the surface. Heavy isidia formation along lobe edge is common. (Stone 2010)
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Fact Sheet for Leptogium burnetiae
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