BC Conservation Data Centre: Species Summary
Heterodermia sitchensis
seaside centipede
| Scientific Name: | Heterodermia sitchensis Goward & Noble | ||||||||||
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| English Name: | seaside centipede | ||||||||||
| Classification / Taxonomy | |||||||||||
| Scientific Name - Concept Reference: | Esslinger, T.L. and R.S. Egan. 1995. A sixth checklist of the lichen-forming, lichenicolous, and allied fungi of the continental United States and Canada. The Bryologist 98(4): 467-549. | ||||||||||
| Classification Level: | Species | ||||||||||
| Species Group: | Lichen | ||||||||||
| Species Code: | HETESIT | ||||||||||
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| Conservation Status / Legal Designation | |||||||||||
| Global Status: | G2 (Mar 2025) | ||||||||||
| Provincial Status: | S2 (Apr 2025) | ||||||||||
| BC List: | Red | ||||||||||
| Provincial FRPA list: | |||||||||||
| Provincial Wildlife Act: | |||||||||||
| COSEWIC Status: | Threatened (May 2021) | ||||||||||
| SARA Schedule: | 1 - Threatened (Jul 2025) | ||||||||||
| General Status Canada: | |||||||||||
| Ecology & Life History | |||||||||||
| General Description: | Thallus foliose, tiny (<2 cm diam), whitish gray to pale greenish gray, sometimes discoloring to blue black, lobes suberect, mostly 1-2mm wide, with marginal cilia; soredia present in urn-shaped lobe tips; lower surface white, partly or wholly lacking a cortex, apothecia occasional, becoming sorediate on the margins; cortex K+Y; medulla K+Y, P+Y (atranorin and zeorin) (McCune and Geiser 2009). | ||||||||||
| Technical Description: | |||||||||||
| Diagnostic Characteristics: | H. sitchensis can be distinguished by the presence of irregularly branched marginal cilia and tiny urn-like structures (aborted apothecia) which contain ring-shaped soralia near the lobe tips (COSEWIC 2006, Stone et al. 2009). It also has no lower cortex (Stone et al. 2009). Physcia adscendens is similar, but its marginal cilia are not branched, its lower surface is corticate, and its soralia are formed on the lower surface below the lobe tips, whereas those of H. sitchensis are formed within immature apothecia on the upper surface of the tips (Stone et al. 2009). H. sitchensis can be distinguished by the presence of irregularly branched marginal cilia and tiny urn-like structures (aborted apothecia) which contain ring-shaped soralia near the lobe tips (COSEWIC 2006, Stone et al. 2009). It also has no lower cortex (Stone et al. 2009). Physcia adscendens is similar, but its marginal cilia are not branched, its lower surface is corticate, and its soralia are formed on the lower surface below the lobe tips, whereas those of H. sitchensis are formed within immature apothecia on the upper surface of the tips. | ||||||||||
| Identification Comments: | Thallus foliose, semi-erect, cushion-forming, about 2 cm across. Lobes thin, stiff, short to elongate, separate to loosely overlapping, 1-2 mm wide, with long thin cilia along the margins. Upper surface of thallus strongly convex, pale greenish white but discolouring to bluish black, often bearing scattered whitish spots (maculae). Lower surface of thallus white, appressed-cottony and unevenly thickened, with strut-like extensions of the lower cortex protruding into the medulla. Spore-producing structures (apothecia) urn-shaped, near the lobe tips, with prominent flaring rims producing powdery asexual propagules (soredia) on their inner surface. Chemistry: atranorin, zeorin, fatty acids. Color tests: K+ yellow (cortex and medulla). The PD+ yellowish to pale orange medullary reaction reported by Goward (1984) has not been confirmed in more recent material (COSEWIC 2006y). | ||||||||||
| Similar Species: | Physcia tenella, another tree-dwelling species with pale greenish lobes lined with cilia, has soredia on the undersides of the lobe tips instead of around the apothecia, and the lower surface of the thallus cartilaginous instead of cottony. Cavernularia hultenii can also sometimes be similar, but the lower surface is black and pocked with tiny pits (COSEWIC 2006y). | ||||||||||
| Global Reproduction Comments: | Spores do not mature, and dispersal is restricted to vegetative propagation via soredia (powdery asexual propagules made up of algal cells and fungal hyphae), litterfall, and fragmentation (COSEWIC 2006, Stone et al. 2009). This species is most likely dispersed by wind or water that carry fragments to new locations, or by birds that feed on invertebrates which live on twigs where this lichen occurs. | ||||||||||
| Provincial Reproduction Comments: | In Heterodermia sitchensis, spores produced in the apothecia are apparently vestigial because they fail to reach maturity. Reproduction therefore appears to be only vegetative, by means of powdery soredia produced on the inner walls of the apothecial urns. Because soredia contain both the fungal and algal partners of the lichen, they are effective propagules, and in contrast to spores, they can establish without having to acquire the algal partner. Lichens can also disperse vegetatively by fragmentation. Soredia and fragments may disperse by wind and by rain, the latter dispersing downward through the canopy in stemflow or throughfall to lower branches (COSEWIC 2006y; J. Christy, pers. comm. 2008). | ||||||||||
| Provincial Ecology Comments: | With the exception of its apparent requirement for defoliated twigs and elevated levels of nitrogen, little is known about the ecology of Heterodermia sitchensis. H. sitchensis is much more strict in its ecological requirements than any of the lichen species with which it occurs, including the related H. leucomela. It is a pioneer species, colonizing early in the development of its host twig. At this stage, the twig is usually devoid of competing epiphytes, allowing H. sitchensis to establish without direct interaction with other species. Within about a decade, however, other epiphytes - mosses, liverworts, and other lichens - begin to colonize the host twig, and H. sitchensis gradually goes into decline. Possibly the high nitrogen concentrations characteristic of twigs supporting H. sitchensis may actually promote the same heavy moss loadings that ultimately displace it. In common with other lichens of small twigs, H. sitchensis appears to be a shortlived species, completing its life cycle within about 10 to 15 years. It dies when its position on a given branch has been usurped by other more aggressive lichens and bryophytes. This observation is probably key to its status as a rare species; for though H. sitchensis has evolved a requirement for frequent recolonization, it appears to be conspicuously inefficient at dispersal and/or establishment. Population dynamics in this species are probably cyclic, with episodes of relative abundance at landscape scale alternating with periods of decline (COSEWIC 2006y). | ||||||||||
| Habitats: (Type / Subtype / Dependence) |
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| Global Habitat Comments: | Heterodermia sitchensis is restricted to coastal habitats and occurs as an epiphyte on Picea sitchensis (Goward 1984, COSEWIC 2021). In British Columbia, it grows on sheltered nitrogen-enriched twigs in the lower canopy of old Picea sitchensis trees in wet, maritime coastal forests within the spray zone of the Pacific Ocean (COSEWIC 2006, 2021). In Oregon, one site is on Picea sitchensis twigs on a ridgetop exposed to ocean winds in old-growth temperate rainforest with Tsuga heterophylla, and the other site is in a Picea sitchensis-Pinus contorta tree island in open dunes with an understory of Cytisus scoparius, Arctostaphylos uva-ursi and Vaccinium ovatum (Stone et al. 2009). Observations from British Columbia suggest that the species requires high levels of nitrogen, restricting it to sites subject to nitrogen enrichment such as sea lion haul-out sites and bird nest sites (COSEWIC 2006, 2021). It also appears to require high humidity in areas that experience frequent fog (COSEWIC 2021). At one site in Oregon, co-occurring lichens include Cavernularia hultenii, Gyalideopsis anastomosans, Heterodermia leucomela, Heterodermia speciosa, Hypotrachyna revoluta, Parmotrema crinitum, Pertusaria glaucomela, Ramalina roesleri, Teloschistes flavicans and Usnea rubicunda. At the other Oregon site, associates include Ramalina thrausta and Usnea spp. (Stone et al. 2009). | ||||||||||
| Provincial Habitat Comments: | In BC, Heterodermia sitchensis is restricted to Picea sitchensis forest along the immediate west coast of Vancouver Island. Habitat requirements appear to be (1) proximity to the ocean and seaward orientation of the site, (2) defoliated twigs less than 12 mm in diameter, with few competing lichens or bryophytes, located within 4-13 m of the forest floor, (3) branches growing less than 10 cm per year, (4) nitrogen and calcium enrichment, and (5) location within the salt spray zone of the Pacific Ocean. Some amount of disturbance from winter storms or insect defoliation may be needed to maintain twig structure and disperse the lichen. Most occurrences are in old-growth, but it occasionally occurs on young trees, typically within about 4 m of the forest floor. It may be sensitive to desiccation, but may also be absent from the middle and upper canopy because of a lack of nitrogen and other nutrients needed for establishment. These elements tend to concentrate only in the lower canopy, perhaps because of leaching from higher in the tree, and may be linked to manuring by seabirds, bald eagles, and marine mammals such as California and Steller's sea lions that gather in the hundreds on some islands. Isolated islands may be favored as refugia by animals and may result in higher occurrence of H. sitchensis. Elevated nutrients may also be linked to calcareous bedrock and a legacy effect from shell middens around now-abandoned First Nations village sites. Other rare lichens in this habitat include Erioderma sorediatum, Parmotrema chinense, and Usnea hesperina (COSEWIC 2006y). | ||||||||||
| Provincial Phenology: (1st half of month/ 2nd half of month) |
Jan: Vegetative / Vegetative
Feb: Vegetative / Vegetative Mar: Vegetative / Vegetative Apr: Vegetative / Vegetative May: Vegetative / Vegetative Jun: Vegetative / Vegetative Jul: Vegetative / Vegetative Aug: Vegetative / Vegetative Sep: Vegetative / Vegetative Oct: Vegetative / Vegetative Nov: Vegetative / Vegetative Dec: Vegetative / Vegetative |
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| Provincial Phenology Comments: | Information on phenology of Heterodermia sitchensis is not available. Thalli are perennial and vegetative growth probably occurs throughout the year except when thalli desiccate during dry spells, at which time they become physiologically dormant. Once developed, apothecia and soredia remain as permanent structures on thallus lobes and presumably release propagules througout the year (J. Christy, pers. comm. 2008). | ||||||||||
| Elevation (m) (min / max): | Provincial: 0 / 100 | ||||||||||
| Known Pests: | |||||||||||
| Pollen Vector: | |||||||||||
| Pollinator: | |||||||||||
| Dispersal: |
ABIOTIC
BIOTIC Birds Water Wind |
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| Provincial Inventory | |||||||||||
| Inventory Priority: | B - Strong | ||||||||||
| Ownership of occurrences (Known locations): | Mixed private/government | ||||||||||
| Inventory Need: | Inventory for Heterodermia sitchensis has been far-ranging and comprehensive, and it seems questionable if further effort is warranted. However, periodic surveys are recommended to monitor habitats for change, particularly at Pacific Rim National Park Reserve, Quisitis Point, Ucluth Peninsula, Wouwer Island, Lawrence Islets, Folger Island, Spring Island, Mission Group Islands, and Dicebox Island. | ||||||||||
| Inventory Comments: | Irwin Brodo searched for this species in the Queen Charlotte Islands in 2000. Field work by T. Goward in 2001-2004 included a total of 120 person-days searching for this species (60 in Pacific Rim National Park, and 30 each on Gwaii Haanas [South Moresby Island] and northern Vancouver Island), and its known range was extended south to Folger Island (48 degrees 49 'N) and north to the vicinity of Kyuquot (49 degree 59' N). Work to date has confirmed early impressions that Heterodermia sitchensis is a rare species with a sporadic distribution. Two hundred and twenty-seven thalli of H. sitchensis in twelve localities have been recorded to date, including two localities that no longer support this species. Sixty-five percent of these thalli, however, were noted at only three of the existing localities. Because epiphytic macrolichens are seldom confined to a single tree species, a careful search of other potential host trees was made, including Alnus rubra, Abies amabilis, Thuja plicata, Tsuga heterophylla, and Taxus brevifolia. These efforts yielded no additional host trees for this lichen. All finds of H. sitchensis to date have been restricted to the outer coast, within the spray zone of the Pacific Ocean. Given the intense level of sampling for epiphytic macrolichens in coastal British Columbia, the strictly seaside occurrence of these lichens does not appear to be an artifact of undercollecting (COSEWIC 2006y). | ||||||||||
| Economic Attributes | |||||||||||
| Provincial Economic Comments: | No commercial or cultural uses are known for Heterodermia sitchensis. | ||||||||||
| Distribution | |||||||||||
| Endemic: | N | ||||||||||
| Global Range Comment: | Heterodermia sitchensis is known from only the very wettest locations along the Pacific coast of northwestern North America in Canada and the United States (COSEWIC 2021). In British Columbia, the species is known from the shoreline on the west coast of Vancouver Island, where it ranges from Kyupot Sound south to the Pacific Rim National Park (COSEWIC 2006, 2021). Two outlying sites are known from Oregon: Cape Lookout in Tillamook County and Umpqua Lighthouse State Park in Douglas County (Stone et al. 2009). An early report from Alaska is based on a misidentification (COSEWIC 2006), and the species is not currently known to occur there. Heterodermia sitchensis is expected to occur in other similar areas of high rainfall within the coastal fog zone (i.e., the Olympic Peninsula of Washington state), though it has not yet been found at any sites in Washington. Range extent was estimated using herbarium specimens and NatureServe Network occurrence data collected between 1994 and 2025 (RARECAT 2024, CLH 2025, NatureServe 2025). | ||||||||||
| Disjunct, more common elsewhere: | N | ||||||||||
| Peripheral, major distribution elsewhere: | N | ||||||||||
| Authors / Contributors | |||||||||||
| Global Information Author: | N. Ventrella (2025) | ||||||||||
| Last Updated: | Mar 19, 2025 | ||||||||||
| Provincial Information Author: | Christy, John A. | ||||||||||
| Last Updated: | Dec 17, 2008 | ||||||||||
| Last Literature Search: | |||||||||||
| References and Related Literature | |||||||||||
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC. |
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Brodo, I. M., S. D. Sharnoff and S. Sharnoff. 2001. Lichens of North America. Yale University Press. New Haven and London. 795 pp. |
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COSEWIC. 2006. COSEWIC assessment and update status report on the seaside centipede Lichen Heterodermia sitchensis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 28 pp. (https://species-registry.canada.ca/index-en.html#/documents?documentTypeId=18&sortBy=documentTypeSort&sortDirection=asc&pageSize=10). |
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COSEWIC. 2006y. COSEWIC assessment and update status report on the seaside centipede lichen Heterodermia sitchensis in Canada. Comm. on the Status of Endangered Wildl. in Can. Ottawa. vi + 28pp. |
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COSEWIC. 2021. COSEWIC assessment and update status report on the seaside centipede Lichen Heterodermia sitchensis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xiii + 40 pp. Online. Available: www.canada.ca/en/environment-climate-change/services/species-risk-public-registry.html (accessed 2025). |
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Goward, T. 1984. Heterodermia sitchensis new from the Pacific Northwest. Bryologist 87(4): 366-368. |
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Goward, T. 1984. Heterodermia sitchensis, a new lichen from the Pacific Northwest of North America. The Bryologist 87: 366-368. |
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Goward, T. 1996. Status report on the Seaside Centipede HETERODERMIA SITCHENSIS in Canada. Rep. submitted to the Comm. on the Status of Endangered Wildl. in Can. (COSEWIC). Ottawa. 33pp. |
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McCune, B. and L. Geiser. 2009. Macrolichens of the Pacific Northwest: Second Edition. Oregon State University Press, Corvallis, Oregon. 448 pp. |
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Parks Canada Agency. 2011. EXCEL spreadsheet of Seaside Centipede plant observations in 2011. |
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Stone, D., with edits by J.A. Christy and R. Huff. 2009 last update. Species Fact Sheet: Heterodermia sitchensis. Interagency Special Status/Sensitive Species Program (ISSSSP) Conservation Planning Documents, U.S. Forest Service (Pacific Northwest Regional Office) and Bureau of Land Management (Oregon/Washington State Office). Online. Available: http://www.fs.fed.us/r6/sfpnw/issssp/planning-documents/species-guides.shtml (accessed 2010). |
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Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.
Suggested Citation:
B.C. Conservation Data Centre. 2025. Species Summary: Heterodermia sitchensis. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 9, 2026).