Pentagramma triangularis ecology
Grows from sea level to 500 m elevation west of the Cascades, mostly in sunny locations such as rock balds (Washington State).
P. triangularis seems to replace Myriopteris gracillima in rock crevices and at the bases of rock outcrops at low elevations in Washington State. It tolerates shade better than M. gracillima and can be found from part shade to full sun in Washington State (it strongly prefers shade in its southern range). It is also found more often in soil, especially at the sunny bases of large rocks. Often associated with highly visible Sedum spathulifolium (blue gray mat on rock, tinged red in higher sun), though the Sedum is more shade tolerant. Also associated with Selaginella wallacei and probably Lomatium utriculatum, Erythranthe alsinoides (wingstem monkeyflower), Arctostaphylos uva-ursi (bearberry), Berberis aquifolium (Oregon grape), Plectritis congesta (Seablush), Micranthes integrifolia (saxifrage), Olsynium douglasii (grass widow) and all kinds of unidentified mosses and grasses (in short anything else that grows on low elevation rock balds). Nearby trees are often Shore Pine and Madrona, along with the usual suspects like Douglas Fir.
In a few places, P. triangularis and M. gracillima occur together or nearly so, notably in Goldstream Provincial Park (Mount Finlayson) and Gowlland Tod Provincial Park (Jocelyn Hill) near Victoria BC (both with extensive south-facing rock formations), and probably other similar rock outcrops in that area. I also found one P. triangularis at Horsethief Butte (where M. gracillima is abundant), and I suspect there is a west/wet (P. triangularis) to east/dry (M. gracillima) overlapping grade in the Columbia gorge where it transects the Cascades, which you can roughly make out on iNaturalist observation maps. It is very abundant on the low south-facing cliffs next to Coyote Wall/Labyrinth.
Like M. gracillima and other Cheilanthoids, P. triangularis responds to summer drought by curling up with abaxial (spore) side outward (and can rehydrate in the fall if it doesn't get too dried up). In winter the leaves often become tinged purple or turn purple in patches or over the entire leaf. I suspect that some plants die back completely in dry/hot summers but I don't have any clear direct observations of this. Direct observation of rehydration in fall rains at https://www.inaturalist.org/observations/135248536
Circinate fiddleheads apparently emerge very early even in northern areas (March or even February in the Columbia transect) and are distinctive (https://www.inaturalist.org/observations/109008924), though they might be confused with small bracken. A bit later there appears to be a characteristic longitudinally crumpled (narrow leaflet) stage (https://www.inaturalist.org/observations/72227893).
Tentative longitudinal study plant 1: https://www.inaturalist.org/observations/135248536
Tentative longitudinal study plant 2: https://www.inaturalist.org/observations/135248965
(at Echo Mountain in Maple Valley, about 1.5 mi round trip hike, about 400 feet elevation gain)
Annotated observations:
Columbia Transect - Basalt cliffs - https://www.inaturalist.org/observations/149290061
Lake Cushman (Olympics) - Tertiary volcanic rocks, Crescent Formation - https://www.inaturalist.org/observations/129830732
Sares Head/Sharpe Park (Anacortes) - Mesozoic intrusive rocks - https://www.inaturalist.org/observations/135060891
Goose Rock (Deception Pass) - Mesozoic volcanic rocks - https://www.inaturalist.org/observations/135063036
Echo Mountain (Maple Valley) -Tertiary intrusive rocks - https://www.inaturalist.org/observations/135248965
Sugarloaf Mountain (Anacortes) - Mesozoic volcanic rocks - https://www.inaturalist.org/observations/136436855
Chuckanut Ridge - Tertiary continental sedimentary rocks - https://www.inaturalist.org/observations/136921299
Other places to look for easy access:
Pigeon Point Park (West Seattle, N end of Duwamish greenbelt) dubious, failed to find in fall wet weather.
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