Botrychium montanum

Mountain Moonwort is a small perennial fern with a single aboveground frond. The frond varies in height but may reach a height of 12 cm. It is a dull, glaucous gray-green, somewhat succulent, and divided into two segments which share a relatively short common stalk. The sterile segment is once pinnatifid with well separated, irregular, angular, ascending lobes with entire or toothed margins. The fertile segment is longer than the sterile segment, is branched, and bears grape-like sporangia. Spores germinate underground and develop into minute subterranean, non-photosynthetic gametophytes which depend on an endophytic fungus for nourishment (Vanderhorst 1997).

The glaucous gray-green color, succulent texture, relatively short common stalk, and irregular angular lobes rather than distinct pinnae are diagnostic of Botrychium montanum. Among the moonworts of Montana, B. montanum is relatively easily recognized, but may be mistaken for B. ascendens; also, small plants may be confused with other species (Vanderhorst 1997). Reliable field determination of moonworts depends on the careful use of technical keys and comparison with silhouette outlines of verified specimens. Identification can be complicated because there is often a high degree of morphological variability between individuals in a population and between populations of the same species; several species may grow together at the same site, and the few diagnostic characters may not be apparent in small plants.

Botrychium montanum occurs under old growth Western Red-cedar (Thuja plicata) on alluvial terraces along small to moderate sized streams where the soil is moist and high in organic matter. Most of the known sites have saturated soils (Potash 1998). In California, it grows in similar conditions under incense cedar (Calocedrus decurrens). It also occurs in fens, seeps and meadows along streams where the substrate is saturated (Farrar 2011). On the Wenatchee National Forest (in Washington), most sites are located in the Tsuga heterophylla/Asarum caudatum plant association (Potash 1998). Though these habitats of dark forest and open meadows have opposite extremes of light, they have in common a continuous supply of moisture and a high mineral content. Some large populations have been found in high elevation meadows in the Northern Cascade Range in northeastern Washington. Species of cedar (Cupressaceae, such as Thuja plicata and Calocedrus decurrens) support endomycorrhizal fungi which are required by species of Botrychium, perennial herbaceous vegetation also supports endomycorrhizal fungi (Farrar 2011). It has been found at elevations from 600 to 2100 meters (SEINet 2021).