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

Dryopteridaceae
Fern
Lemmon's holly-fern, Shasta fern

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

descending from Long's Pass, in serpentine soil, Kittitas County, Washington, USA

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