Polystichum lemmonii (Shasta Fern)
Polystichum lemmonii (Lemmon's holly-fern, Shasta fern) is my favorite fern, and I spent some time looking at it on this field trip. It is in the Dryopteridaceae family
Polystichum lemmonii the signature fern for serpentine soil. Arthur Kruckeberg: "Of the western ferns on serpentine, only Polystichum lemmonii is obligate,"
Source Hardy Fern Library
"Kruckeberg pointed to one fern, Shasta holly fern (Polystichum lemmoni), which is exclusively found in the Pacific Northwest only on serpentine. Asked how this fern could be found so widespread, Kruckeberg pointed out that airborne spores do the trick. To this he states Beijerinch's Law "Everything is everywhere, but the environment selects." This fern regenerates from the spores, and as he noted, so do a couple of other ferns regenerate on serpentine. These, however, can be found on other soils, too. The answer as to why and how endemic floral seeds spread and regenerate on serpentine from distant places is still unanswered."
A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle.
The soils derived from ultramafic bedrock give rise to unusual and sparse associations of edaphic (and often endemic) plants that are tolerant of extreme soil conditions, including:
low calcium:magnesium ratio, lack of essential nutrients such as nitrogen, potassium, and phosphorus and high concentrations of the heavy metals (more common in ultramafic rocks)
These plants are commonly called serpentine endemics, if they grow only on these soils. (Serpentinite is composed of the mineral serpentine, but the two terms are often both used to mean the rock, not its mineral composition.)
Source: en.wikipedia.org/wiki/Serpentine_soil accessed 14 Aug 2010
Bean Creek Trail 1391.1, 1340 meters, 4400 feet, Teanaway, Kittitas County, Washington
Northwestern Chapter of North American Rock Garden Society (NARGS) field trip on 30 June 2012