Montana Field Guide

Plants: Small, strongly clumping ferns that have two types of pinnately-dissected fronds: the spore-bearing leaves that are upright, and sterile leaves that are more narrow (Alverson 1989). Rhizomes, including old petiole bases, are 4-8 mm wide and vary from upright to nearly horizontal. They are densely covered with lanceolate to linear scales that can reach 6 mm long and 2 mm wide (Alverson 1989).

Leaves: In outline the leaf blades are triangular to narrowly egg-shaped. The blade ranges from being half the length to the same length as the petiole. They are delicate, two to three times pinnate, and become translucent when dry (Lesica 2012). Petioles collapse inward when dry, and then measure 1 mm across (Alverson 1989). Sterile leaves are hairless, 3-20 cm long, and deciduous. The leaflets generally have wedge-shaped bases and range from oblong to fan-shaped, and are regularly toothed on the upper half or third, with some teeth cutting more deeply than others. Spore-bearing leaves are 5-25 cm long, with 3-12 mm long linear segments (Alverson 1989).

(Contribution of Lesica et al. adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

Leaves grow in spring and die back in fall; spores mature late summer to fall (Alverson 1993).

Cryptogramma cascadensis was distinguished from the more widespread Cryptogramma acrostichoides in 1989 (Alverson 1989). In comparison, C. cascadensis grows in moister microsites. It has deciduous fronds, typically leaving few remnants by the next year, whereas C. acrostichoides has thicker, leathery, mostly evergreen fronds, and old, dead leaves that accumulate at the base of the plant. C. cascadensis has grass green leaves that are similar in color above and below; mature C. acrostichoides leaves are darker green with a contrastingly lighter underside (Alverson 1989). Also look for tiny, appressed hairs on both surfaces of C. acrostichoides fronds – especially on the rachis (use a hand lens) – which are essentially absent on C. cascadensis (Harvey 2015; Alverson 1989). In dried specimens, the stipes provide some useful distinctions: those of C. acrostichoides are more rigid, and remain about 2 mm in diameter, whereas dried stipes of C. cascadensis collapse inward and measure only 1 mm across (Alverson 1989).

Our other species of rockbrake, Cryptogramma stelleri, has leaves scattered along an elongated rhizome instead of in dense tufts, its petioles are dark brown in at least the basal half, and it typically grows on calcareous material (Alverson 1993).

Aspidotis densa is a small fern that can be found in similar rocky habitats, but its petioles are dark brown, whereas those of Cryptogramma cascadensis are greenish to straw-colored, and dark brown only in the basal 1/8 (Hitchcock and Cronquist 1973; Alverson 1993). Also, Aspidotis leaves are not as strongly dimorphic, and the fertile pinnules have a firm, abruptly narrowed tip that Cryptogramma pinnules lack (Hitchcock and Cronquist 1973; Lesica et al. 2012).

Rocky subalpine areas in relatively moist areas of the Rockies, typically on igneous rocks (granite or extrusive types), and often in microsites with substantial winter snowpack (Alverson 1989). Habitats of Montana specimens include talus slopes, cliffs, and sites near boulders (Lesica 2012, CPNWH 2017).

While C. acrostichoides is adapted to survive dry periods, (fronds become curled and brittle and then rehydrate with the reappearance of moisture), C. cascadensis apparently is not, because when water was withheld in a garden setting its fronds withered and died (Alverson 1989). With its thin, deciduous leaves, this species seems well-adapted to long, snowy winters, followed by relatively moist conditions during the growing season (Alverson 1989).

Processes that affect plants growing on talus slopes include erosion and deposition, rockfalls, and avalanches (Perez 2012). Large cobbles are substantially more stable than smaller-diameter substrates, and retain more moisture near the surface (Perez 2012). In many talus plants, most belowground biomass grows uphill, perhaps due to gradual burial as sediment creeps downhill (Perez 2012). Plants may adapt to these harsh conditions by growing close to the ground, minimizing exposure to geological hazards (Perez 2012). Most talus plants are perennials, and many are able to reproduce vegetatively – an advantage when growing on these shifting surfaces (Perez 2012).

Spore sacs are in round to oblong clusters that are covered by the curled-under margins of the fertile leaves. When mature, these clusters (sori) merge (Alverson 1989; Alverson 1993).

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).