Montana Field Guide

PLANTS: Acaulescent (without stems), herbaceous perennials from a short, scaly rhizome that is usually covered with old leaf bases. Source: Lesica et al. 2012.

LEAVES: Fronds appear similar (monomorphic), 15–75 cm long. Petioles are shorter than the blade with tan scales toward the base. Blades are light green, ovate, non-glandular, and twice pinnate at the base. Pinnules (leaflets) are deeply pinnately lobed or toothed. The first downward-pointing pinnule on the lowest pinnae is less than twice as long and wide as the opposing upward-pointing pinnule. Source: Lesica et al. 2012.

INDUSIUM: Broadly horseshoe- or kidney- (Reniform) shaped, which is attached off-center of the sorus. Source: Lesica et al. 2012.

Spinulose Shieldfern sheds its spores over 2.5 months, usually beginning in 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):

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.

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 grows in shady mesic forests in Montana, often with western red cedar or hemlock within the montane and subalpine zones (Lesica 2012). In general, Spiny Shieldfern prefers semi-shaded (Runk et al. 2012), moist habitats with medium-nutrient rich and somewhat acidic soils (Munger 2007).

FOREST SUCCESSION [Adapted from Runk et al. 2012]
Spinulose Shieldfern generally increases in abundance after disturbances from logging or large-scale windthrow, especially where tree and shrub regeneration is sparse. It is abundant through early and mid-successional stages of forest development, but decreases in abundance as understory diversity increases.

Spinulose Shieldfern has been found to support arbuscular mycorrhizae to varying degrees (Runk et al. 2012).

CULTURAL [Adapted from Runk et al. 2012]
Northern Coastal people used species of Dryopteris as food. In the spring young fronds are eaten. In the fall rhizomes and stalk bases are collected to steam or roast. Roots pounded into a paste were applied to cuts. Roots, which are flammable, were used as a slow match. Fronds soaked for several days were used as a hair wash.

Spinulose Shieldfern reproduces by spores, rhizomes, and sporophyte crowns (Runk et al. 2012). Reproduction can produce male-only plants, female-only plants, and bisexual plants. Spores can be produced by self-pollination or cross-pollination (Munger 2007).

HYBRIDIZATION
Spinulose Shieldfern can hybridize with five other species of Dryopteris, including D. intermedia and D. expansa (D. dilatata) (Montgomery and Wagner Jr. in FNA 1993); Runk et al. 2012). Spinulose Shieldfern is a tetraploid, which means it has four homologous sets of chromosomes per cell. Spinulose Shieldfern is itself a viable hybrid of Dryopteris intermedia and a hypothetical ancestral species, Dryopteris semicristata. Sterile hybrids have misshapen spores and intermediate morphology (Montgomery and Wagner Jr. in FNA 1993).

LIFE CYCLE [Adapted from Runk et al. 2012]
Spores begin to shed from sori on mature fronds in summer. Spore dispersal lasts for about 2.5 months. The spores then germinate and grow a long multi-cellular filament that extends into the soil. The gametophyte, given favorable conditions, then grows further, becoming flat and heart-shaped. Male reproductive organs (antheridia) are developed first in the gametophyte. About 9 weeks after the spores are sown, female reproductive organs (archegonia) form. Eggs within the archegonia are then fertilized and new sporophytes are produced. Fronds of the sporophytes appear approximately 28 weeks after spores are sown. In approximately another 14 weeks these fronds develop a species specific appearance and can be identified.

Depending on when spores are sown, sporophytes may be produced in the autumn or spring. If sporophytes are produced in autumn, they overwinter attached to the gametophyte. Spores can infrequently stay attached through the winter and germinate as late a March. Fronds mature by June.

Spores primarily disperse by wind, but also by water. A Spinulose Shieldfern can produce 150 million spores over its life time. Most of these spores are deposited within three meters of the source plant.