More detail on my Artemisia longifolia observations - originally written for project start in 2021
The apparent problem: the morphological variation of northern Canadian populations of Artemisia longifolia Nuttall is not well understood and is creating some nomenclatural confusion.
Following an arc from SE Alberta into NE British Columbia, A. longifolia can be seen to progress from its typical small, gray-aspect form found on hard, very dry clay badlands slopes, into a sometimes very large, lush green-aspect form found on either loose, relatively moist, slumping slopes or level cobble bars.
The Illustrated Flora of BC recognized the BC Peace River region plants as A. longifolia (while remaining a bit vague about the variability of forms); the taxon is described as “...rare in NE BC, known only from the Peace River drainage near the AB border; E to SK and S to SD and CO”.
Due to increased botanical work in the BC Peace River region in the past 15 years, the large, lush forms of A. longifolia started to be better documented. The taxon’s remarkable similarly to the old name A. herriotii Rydberg was noted and here is where the confusion arose: the BC Conservation Data Centre decided to recognize the name A. herriotii in place of A. longifolia, I think as a marker for these large, lush plants that appear so different from the typical form. However, the name A. herriotii is currently considered an accepted synonym of A. ludoviciana ssp. ludoviciana by the Flora of North America; for those of us familiar with both taxa and their habitats, it is quite obvious that these are different plants!
So, I decided to try to find out what was going on. My initial assumption was that the BC Peace River region plants were a distinct taxon, and that I would find a clear break somewhere in Alberta where the A. longifolia dropped out and the A. herriotii form took over. I’ve now collected at a number of representative sites in AB and numerous sites in the BC Peace region. The result is that I cannot see a clear break; instead, the plant form and the habitat gradually shift from SE AB to NE BC. Therefore, my current feeling is that all the plants are A. longifolia, with the change in form going hand-in-hand with the change in available habitats and increased moisture as one moves north and west.
This is very much a work in progress. There are many more sites I’d like to visit in AB, and I continue to search iNaturalist Artemisia observations in order to pinpoint more locations of both of these forms of A. longifolia. So, stay tuned!
Here is what the observations I have made so far are trying to show:
-A. longifolia in SE AB is generally found on dry, hard clay slopes and is a relatively smaller plant with a gray aspect, although it is possible to find some plants growing on slumping banks quite near water, and it is possible to find greenish-aspect, somewhat larger plants in these areas (examples: Dinosaur Provincial Park & Little Bow Provincial Park, AB).
-In central AB, one finds plants of both gray and green aspect and of variable size growing together at the same site, still mostly on hard clay soil but with more moisture apparently available (to judge by the surrounding plant communities and nearby bodies of water) (examples: Rolly View, Edmonton, & Dunvegan, AB).
-Key transition sites have both dry, hard clay slopes supporting smaller gray-aspect forms and moist, looser soils supporting larger green-aspect forms (Dunvegan, AB & Clayhurst, BC).
-The remaining sites so far seen by me in NE BC fall into two types:
---Main habitat: quite large patches of hundreds or thousands of plants on open, steep, loose, slumping slopes along the Peace River in particular, but also along other rivers and large streams in the region. Large patches have also been found on similar loose soils at large, open hillside seeps (not far from a stream or river). The A. longifolia plants at these sites are often quite large and lush when well established (examples: Peace River upstream of Kiskatinaw River, Bear Flat, Halfway River).
---Secondary habitat: scattered single plants or small patches of plants on open to shaded, level river shore cobble bars (active or stabilized) or cutbanks. The A. longifolia plants at these sites can be large but are generally mid-sized to small (examples: Peace River at Blackfoot Park, Peace River near the Beatton River).
-Aspect, leaf forms, and array forms vary considerably from SE AB to NE BC, but all plants key to A. longifolia if one allows that the possible lack of northern Canadian material for study by the FNA authors limited their understanding of the maximum plant, leaf, and array sizes.
-Other features such as bicolor leaf faces, leaf margins, occasional large leaf lobes, and size of individual flower heads remain consistent across the range and remain very close to the description of A. longifolia as given in FNA.
-UPDATE: as of 2023, the BCCDC returned to the use of the name A. longifolia for all NE BC plants. This is really helpful, since it prevents any confusion with A. ludoviciana var. ludoviciana, a different plant with a different range and habitat preference.
Of note, things are even more confusing in central Alberta, where the name A. tilesii also comes into the mix for these large, lush plants, as seen in these specimens at ALTA:
https://photos.app.goo.gl/PDsWJJ5fXy2oQjtu8
There are a few observations in Edmonton being called A. tilesii that I feel would be better called A. longifolia, but I have yet to visit those. My feeling is that, like at the A. longifolia sites I have already seen in the Edmonton area, these other sites when taken as a whole will have plants with both lobed and simple leaves on the same plants.
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