Montana Field Guide

Crested Shieldfern is an herbaceous perennial with clustered fronds arising from a short rhizome. The stalked fronds have narrowly elliptic blades pinnately divided into numerous pairs of pinnately lobed leaflets, or pinnae. The fertile fronds, 3-6 dm long, are erect and deciduous, while the sterile ones are evergreen, smaller, and more lax. Clusters of spores, or sori are borne along either side of the pinnae midveins on the underside of fertile fronds. Sori are covered by a whitish, broadly horseshoe-shaped membrane, or indusium.

Mature fronds in July-August, spores in early July.

The broadly horseshoe-shaped indusium identifies its members as Dryopteris.

The length ratio of downward- to opposing upward-pointing pinnules on the lowest pinnae separates Spinulose, Spreading, and Male ferns (Giblin et al.[eds] 2018; Lesica et al. 2012):

Crested Shieldfern - Dryopteris cristata, native, SOC:
* Leaves are 1-pinnate and of two types: erect fertile fronds are taller than the sterile arching, evergreen fronds.
* Petiole is less than half as long as the blade.
* Leaves are narrowly lance-shaped in outline.
* Pinnae are deeply pinnately lobed.

Spinulose Shieldfern - Dryopteris carthusiana, native:
* Leaves 2- or 3-pinnate at base and deciduous.
* Petiole is often shorter than the blade.
* Leaves are broadly ovate to triangular in outline.
* Leaf bladed about one-half to two-thirds as wide as long (except in very robust plants).
* The first downward-pointing pinnule on the lowest pinnae is less than twice as long and wide as the opposing upward-pointing pinnule.
* Teeth on pinna margins with a prominent spine tip about 0.05 mm long.
* Leaves deciduous.

Spreading Woodfern - Dryopteris expansa, native:
* Leaves 2- or 3-pinnate at base and can be more evergreen.
* Petiole is often about half as long as the blade.
* Leaves are broadly ovate to triangular in outline.
* Leaf blade is about one-half to two-thirds as wide as long (except in very robust plants).
* The first downward-pointing pinnule on the lowest pinnae is at least twice as long and wide as the opposing upward-pointing pinnule.
* Teeth on pinna margins toothed with a spine tip less than 0.03 mm.

Male Fern - Dryopteris filix-mas, native:
* Leaves are 1- to 2- pinnate at the base and deciduous.
* Petiole is about one-third or less the length of the blade.
* Leaves are narrowly elliptic or lance-shaped in outline.
* Downward- and upward- pointing pinnules are about equal in length and width.

Moist to wet, often organic soils at the forest margins of fens and swamps in the montane zone.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Crested Shieldfern include populations where Canada Thistle (Cirsium arvense) and Reed Canarygrass (Phalaris arundinacea) are established and have potential to completely occupy its habitat. Trampling due to off-highway vehicle (OHV) activity contributes additional impacts at one site despite restrictions on OHV travel at this location. Water management actions are a reported threat to a small population found at a reservoir, where water diversion or inundation of habitat is a credible risk (MTNHP Threat Assessment 2021).