Regularity: Regularly occurring
Regularity: Regularly occurring
Global Range: Occurs primarily in eastern Alberta along the North Saskatchewan and Athabasca River drainages and in at least the southern half of Saskatchewan; sites are also known from North Dakota (McLean and Burleigh counties), the Northwest Territories near the Alberta border, west-central Manitoba near the Saskatchewan border, and northeastern Manitoba. The Manitoba Conservation Data Centre considers this species to be "reported but unconfirmed", indicating that Manitoba sites would benefit from verification. Range within Alberta alone is believed to be >100,000 km2, although available habitat within this area has a considerably smaller extent (T. Kemper pers. comm. 2008). The map presented by Cantino (1981) suggests a range extent of around 500,000 km2 overall.
Table 1 of Cantino (1981) summarizes characters differentiating this species from its putative parents, P. parviflora and P. virginiana. Genetic work would yield certain separation (2n = 76 in P. ledinghamii vs. 2n = 38 in P. parviflora and P. virginiana), but in the absence of such data, a combination of morphological characters can be used. The two characters in which P. ledinghamii resembles neither putative parent are its larger nutlets (2.8-4.0 mm vs. 2.1-3.3 mm in P. parviflora and 2.5-3.2 mm in P. virginiana) and its slightly larger inflorescence trichomes (0.14-0.225 mm vs. 0.075-0.15 mm in P. parviflora and 0.075-0.15(-0.20) mm in P. virginiana) (Cantino 1981). Further characters distinguishing it from P. parviflora include larger flowers (14-23 mm long vs. 9-16 mm long on dried specimens), majority of stem leaves always sharply serrate (vs. sometimes with majority of stem leaves bluntly toothed), and leaves widest above to below middle but usually not near base of blade (vs. leaves widest near or below middle of blade, never above middle, the upper pairs usually widest near base of blade) (Cantino 1981, 1982). Further characters distinguishing it from P. virginiana include upper leaves always clasping the stem (vs. almost never clasping the stem) (Cantino 1981).
Comments: Low, moist to wet woods; swampy, somewhat exposed areas along lake/pond shores, river and stream banks; river floodplains and flats; sloughs and ditches; and wet meadows and marshes. Habitats are often subject to intermittent flooding. Associated species include Mimulus ringens, Eleocharis palustris, Mentha arvensis, Stachys palustris, Ranunculus macounii, Anemone canadensis, Poa palustris, Geum aleppicum, Veronica scutellata, Polygonum amphibium, Calamagrostis canadensis, Mentha arvensis, and Cicuta maculata.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 21 - 300
Comments: Of the five jurisdictions in the range, only Alberta tracks element occurrences; there are 24 known occurences in Alberta, though 8 of these are older and should be revisted (T. Kemper pers. comm. 2008). Cantino (1981) shows 17 sites in Saskatchewan, although this is almost certainly an underestimate since he does not claim to be comprehensive in his specimen list for P. ledinghamii, and he shows just 8 sites for Alberta. Harms (2003) considers the species "common" in Saskatchewan, also suggesting much more than 17 sites. Cantino's (1981) records for the other three jurisdictions seem to be more on par with current knowledge; he shows 2 sites in North Dakota (McLean and Burleigh counties), 1 in the Northwest Territories near the Alberta border, 1 in west-central Manitoba near the Saskatchewan border, and 1 in northeastern Manitoba. The Manitoba Conservation Data Centre considers this species to be "reported but unconfirmed", indicating that Manitoba sites would benefit from verification.
National NatureServe Conservation Status
Rounded National Status Rank: N4 - Apparently Secure
Rounded National Status Rank: N2 - Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G4 - Apparently Secure
Reasons: Occurs primarily in the southern half of Saskatchewan, and in eastern Alberta along the North Saskatchewan and Athabasca River drainages; a few sites are also known from adjacent Northwest Territories, North Dakota (McLean and Burleigh counties), and probably Manitoba. Alberta is the only jurisdiction that has mapped element occurrences, of which there 24 known in Alberta. At least 17 sites exist in Saskatchewan (based on literature reports), probably some to many more as the species is ranked "common" in Sasketchewan by a recent checklist. Some sites in Alberta contain hundreds of "plants" (possibly ramets), although few have been counted recently. Short-term trend is believed to be relatively stable and threats relatively low, at least in Alberta, although some occurrences may potentially be at risk due to industrial activity (oilsands mining).
Environmental Specificity: Narrow. Specialist or community with key requirements common.
Comments: The species predominantly inhabits riparian areas (T. Kemper, pers. comm. 2008).
Global Short Term Trend: Relatively stable (=10% change)
Comments: Believed to be relatively stable in Alberta (T. Kemper pers. comm. 2008); this seems a reasonable estimate rangewide as well.
Comments: In Alberta, some occurrences along Athabasca River and associated tributaries may potentially be at risk due to industrial activity (oilsands mining); threats in Alberta are estimated to be Low in Scope but Unknown in Severity and Immediacy (T. Kemper pers. comm. 2008). Threats in the rest of the range are unknown at this time.
Biological Research Needs: Confirm taxonomic status, identification of herbarium records, distribution reports.
Relevance to Humans and Ecosystems
Stewardship Overview: Maintenance of the hydrological regime is probably important for this riparian species; Vujnovic et al. (2005) describe its preference for a specific riparian zone at one Alberta site.
Names and Taxonomy
Comments: Believed to be a tetraploid derivative of hybridization between Physostegia parviflora and P. virginiana (Cantino 1981); apparently, there is little other evidence of natural interspecific hybridization in this genus (Cantino 1982). Cantino (1982) allows that "the phenetic difference between Physostegia ledinghamii and P. virginiana is sufficiently low that, when compared to the interspecific phenetic differences elsewhere in the genus, it is unclear whether the two taxa should be treated as species or subspecies." However, he feels that "the evidence that P. ledinghamii is a tetraploid derivative of a hybrid between P. virginiana and P. parviflora swings the balance in favor of treating it as a distinct species" (Cantino 1982).
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