Two plants growing together.

Alluvial forest in large river valley. Just a little further from the hillside edge than the other plants of this species found in the area, but not far.

Habitat characterized by being slightly brighter (less dense high tree canopy), shrub layer of salmonberry & vine maple, and somewhat mounded ground surface. Only scattered green groundcover (Maianthemum etc), whereas flatter areas had a much more lush groundcover.

Group of 3 plants growing together. Under Salmonberry/Vine Maple, in flat alluvial forest but very near edge of steep hillside.

Near other known small populations, but it took another 45min of bushwacking before finding these new ones.

Fresh fronds just starting to grow for the season.

Large group of plants at base of limestone cliffs.

This population at Horne Lake was first reported by @rambryum 3 years ago.

I saw about a dozen groups of plants along the cliff base, over about 150m. All were strictly associated with the cliff base, with a couple of the furthest "outliers" being only a couple of yards away into the forest. The cliffs were near vertical for the most part (and hence don't even show in the Google satellite view of the location) with no opportunities for any plants to grow higher up, and then moderately dry Douglas-Fir forest on a medium-steep slope at the base of the cliffs, continuing down for about 100m to the large lake at the base

P. munitum was abundant in the forest below, but generally absent from the immediate rocky cliff base, so plants were easily distinguishable by habitat/location. I did not observe any P. imbricans in the area.

The access was far easier than I had expected. I was fearing a steep bushwack and/or boulder scramble, but there was a well developed climber's trail through solid evergreen forest on the approach. While it was overcast on my visit, it looked like this location would be quite shady throughout the day due to the forest at the base of the cliffs, despite the south facing exposure.

There was quite a variety in the depth of divisions in the leaflets, with the small heavily twisted plants being the most deeply incised, and mostly clearly recognizable as this species. The texture of the leaflets was extremely heavy, noticeably more robust than P. munitum, and still in very fresh condition given the season. Other individual plants growing in soil rather than directly on rock were larger and less deeply divided - like the large one pictured at the front here (feel free to debate potential hybrid with munitum, but they did seem to form a continuum from small & deeply divided at the back, to large and less divided at the front). These looked very similar to P. andersonii to me, and at any other location I may well have mistaken them. All were checked carefully for any bulblets, of which none were found. Other small plants found in sheltered locations, while mature, where noticeably softer and more rounded.

I'll upload more photos of the rest of the plants later this week.

The very same fern as https://www.inaturalist.org/observations/179649516
Certainly one of the most vigorous and best shaped Hard Shield Fern i do know in my home region.
The large fronds are clearly bipinnate, largest forwards directed pinnulae beside leaf midrib are partially pinnate, so this fern's leaves are the same dissected as with large Polystichum setiferum, it's ancestor.
Still the fronds are leathery stiff, with glossy upper side, more bright to slightly yellowish green. Leaf stipe shorter than with P. setiferum, lowest pinnae relatively long, but clearly shorter than longest ones. It's rather bright to yellowish green upper surface is uncommon with P. aculeatum, might be due to growth condition, sunny from east side.
See as well at flickr album Polystichum aculeatum "forma parangulare".

It was the third day i watched out for this most rare fern at the serpentine mountains Kirchkogel and Trafössberg. I had seen it many years ago there, but did not remember the accurate sites. The ones here was my second find, and i found a few others at two distant places.
All these "Fur ferns" remained only at vertical flanks of serpentine rocks, where they were save from getting browsed by chamois, Rupicapra rupicapra or Mouflon, Ovis aries ssp. musimon.
All together i might have seen likely less than 20 individuals at three rocks, and i do expect this population is dying out, as it seems hardly to reproduce.