Marginal shield fern is perennial, growing in clumps from rhizomes with orangish-brown scales. At the base of the cluster of fronds, the rhizome, with its scales and remnants of old leaf stalks, looks something like the trunk of a miniature palm tree. The leaves are evergreen, leathery, hairless, flat, up to a yard long, and are ovate to lance-shaped to narrowly ellipse-shaped in general outline. At their outer tips, they are pinnately compound; below, they are usually twice-compound. The leaflets reach 4¾ inches in length and are narrowly triangular to linear, the margins untoothed or shallowly toothed; the subleaflets unlobed to deeply lobed. The basal lower segment of the basal leaflets is 1–3 times longer than the basal upper segment, and it is not the same length as the adjacent basal segment. Spore clusters are near the margins of the leaflets or leaflet lobes. The kidney-shaped indusium that partially covers each spore cluster is hairless, thick, and does not shrivel at maturity. Spores are produced June–October.
Similar species: Missouri has 6 species of wood ferns (genus Dryopteris), all with scaly rhizomes, straw-colored leaf stalks, and leaves that look like typical “lacy” fern leaves. Our other 5 wood ferns are:
- Spinulose wood fern (D. carthusiana) is uncommon and widely scattered in eastern and central Missouri, on moist forested slopes, often on acidic substrates, swamps, and other shaded, moist habitats. Its rhizome and petiole scales are tan and not shiny. The leaf blades and indusia lack hairs or tiny glands.
- Log fern (D. celsa), uncommon in the southern portion of Missouri’s Ozarks (Carter, Howell, and Oregon counties), occurs along moist, shaded spring branches and similar habitats. Its rhizome and petiole scales are dark brown, sometimes with lighter edges, and shiny.
- Crested shield fern (D. cristata) is uncommon and known only from far northeastern Missouri (Clark County), in bottomland wet hummocks near a spring. Missouri is on the southwestern boundary of this plant’s overall range. Its overall leaf shape is narrow, with the leaflets of the fertile leaves twisted like venetian blinds at right angles to the plane of the leaf.
- Goldie’s fern (D. goldiana), uncommon and widely scattered, occurs mostly south of the Missouri River, along spring branches, in moist forests and ravines, and in other shady, most locations. Its leaves can be 4 feet tall.
- Evergreen (or glandular) wood fern (D. intermedia), uncommon in the eastern Ozarks, lives on shaded ledges of sandstone bluffs. Rhizome and petiole scales are tan, not shiny. Leaf blades often have tiny glands along the central axis and the midribs, and notably the spore cluster covers (indusia).
Habitat and Conservation
Ferns have a two-part life cycle. The plants we usually see are sporophytes, which produce spores. Spores germinate into gametophytes, which represent the second part of the life cycle. Gametophytes are small leaflike plants that produce gametes — eggs and sperm. When a sperm fertilizes an egg, a new sporophyte plant develops, completing the cycle.
Members of many fern groups form natural hybrids when they grow close together. This genus is no exception. Marginal shield fern has been documented to hybridize with some 10 other Dryopteris species.
This elegant, evergreen, nonspreading fern can be grown in natural-themed gardens among rocks and flowers, in moist, well-drained soils in shady locations. Always obtain your landscaping plants from reputable sources, or learn how to propagate them yourself from spores. Never dig plants from wild locations.
Marginal shield fern got its name, in part, because the spore clusters (sori) are positioned along the edges (margins) of the leaves. The “shield” part of the name refers to the flaplike coverings (indusia) shielding the spore clusters.
The leaves of this fern are apparently toxic, or at least distasteful to mammals such as deer and rabbits. They rarely eat this plant. The plant is toxic to humans if eaten.
Certain species of aphids, and perhaps other insects, feed on this fern.
Marginal shield fern, in protected places, is evergreen. It and Christmas fern are our two most common ferns seen on wintertime hikes. Being evergreen, these two ferns can conduct photosynthesis on warm winter days. Also, they can take advantage of sunny days in early spring and late fall, when leafless trees permit sunshine to reach the forest floor.
Small animals can take cover under the arching fronds of this fern.