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Ferns of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

Royal Fern thumbnail

Common Name
Royal Fern (American Royal Fern, Flowering Fern)

 

Scientific Name
Osmunda regalis L.

 

Plant Family
Osmundaceae (Royal Fern Family)

Garden Location
Woodland

 

Prime Season
Spring to Late Summer

 

Fern terms

 

Royal Fern up close resembles a member of the pea family or a small locust tree due to the shape of its leaves. Its arching fronds grow several feet in height. It grows from a semi-erect rhizome, with the ground level base of the fern looking like a tussock due to the remains of old stipes.

Fronds: Fronds are either sterile or fertile. Sterile fronds are oblong but highly variable in shape. The fronds have 6+ pairs of pinnae, widely separated, which are again separated into pinnules, which are also widely separated giving the whole frond a resemblance to the leaves of pea family plants. The pinnae are angled upward toward the tip of the frond. The fertile fronds are similar to the sterile ones in the lower and middle sections of the blade, but at the blade tips they are much reduced in size and there is a cluster of smaller, branched, sporangia-bearing pinnules, light to dark brown in color after maturity, green before and at maturity.

The pinnules of this fern are oblong with rounded tips and like the pinnae, are also angled but outward toward the tip of the pinna. Each pinna is divided into 8+ pair of pinnules. These are narrowly oblong, also with rounded tips, and their bases are also rounded and attached with a small stalk, in a mostly alternate manner, to the costa of the pinna. Their main vein is distinctive. Those pinnules near the tip are sometimes longer with a semi-ear. The rachis of the blade is round with a groove on top, pinkish to greenish in color, with fine hair. The stipes are smooth, except will have fine hair when young; they color toward pink-reddish at the base - the color they had emerging from the rhizome. The lower part of the stipes have small stipules - resembling wings.

Fertility: Like the other Osmundas, there are no sori, the sporangia are naked and borne directly on the fertile pinnules in short stalked clusters; bright green when mature and then moving to dark brown after spore dispersal. This arrangement in clusters on the upper pinnules led to the "Flowering Fern" common name.

Fiddleheads: These do not have hair and are pale pink to wine color as they emerge. They should not be eaten as fiddleheads of the Osmundas are known to be carcinogenic.

 

Habitat: Royal ferns like wet feet. They should have consistently wet, acidic, humus rich soil, sun or shade as long as the soil is wet.

Names: The genus Osmunda has an obscure derivation. Some believe it is named after an early Scandinavian writer Osmundus and some say it is named for Osmunder, a Saxon name for a Celtic god, Thor. The species regalis means 'royal' or 'of outstanding merit'. The author name for the plant classification, 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Comparison ferns: There are three that could be confusing - Cinnamon Fern (But there the fertile fronds are separate with their pinnae appressed to the rachis), Interrupted Fern (fertile parts are on a mid-section of the frond between [interrupts] the green pinnae, not at the tips) and Ostrich Fern (fertile frond is also separate but the pinnae arch outward from the rachis, not appressed like the Cinnamon). Only Royal Fern of the Osmundas has the naked sporangium at the top of a frond with green pinnae only below on the frond, and the winged stipes.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Royal Fern Royal Fern Pinnule

Above: The fronds of Royal Fern have a pinkish-color rachis along which the upward angled pinnae are well spaced; each pinnae subdivided into separate pinnules (second photo) which have a small stalk and distinctive main vein. Note the pinnules are angled outward toward the tip of the pinna.

Below: 1st & 2nd photos - Fiddleheads of Royal Fern. The stipe has fine hair when young. 3rd photo - Note the wide separation vertically of the tiers of pinnae.

royal Fern fiddlehead Royal Fern Fiddlehead plant

Below: Fiddleheads - with their pale pink to wine stem color.

young fiddeheads

Below: 1st photo - The tip of a fertile frond with the sporangia bearing pinnae at maturity. 2nd & 3rd photos - The sporangia of Royal Fern. The bright green sporangia are ripe and have started to disperse the spores. They do this through the slit at the top of each sporangium, looking like little Pac-men. After dispersing spores they begin to turn brown, progressing from light to dark before decaying.

royal fern fertile frond Royal Fern green sporangia Royal Fern Brown sporangia

Below: Royal Fern grows from a semi-erect rhizome, with the base of the fern at ground level looking like a tussock due to the remains of old stipes.

Tussok

Below: A group of fertile fronds after the spores have been released.

Group

Below: A group of sterile fronds. The stipes are usually free of pinnae om the lower 1/4 to 1/3.

full plant

Notes:

Notes: Royal Fern was introduced to the Garden by Eloise Butler who first brought it in on May 31, 1907 with 2 transplants from White Bear Lake (North metro area). She planted more in 1908 sourced from Mahtomedi MN. Then on Sept. 29 1914 she found it to be indigenous when she discovered it growing in the "swamp". She wrote: "Much to my surprise I found a single specimen, not large, but beyond the period of childhood, in the center of the swamp where it had not been consciously planted. The query is, how did it get there? Possibly in the sod from some other plantation, for it is too soon for it to develop from the spores of the introduced specimens. The fern is abundant in a thicket about two and one-half miles from the garden." From Ferns in the Wild Garden June 1915, unpublished. She planted 3 more in Oct. 1920 from Horsford's Nursery in Charlotte VT.

Curator Martha Crone brought in 8 in 1935, more in '47, 55 in 1956 when she was developing the new Fern Glen (plants from The Three Laurels, Marshall NC) a few more in 1957 and recently Curator Susan Wilkins planted 6 in 2006. Like the Cinnamon Fern, Royal fern is found in the eastern half of North America, with Minnesota and Alberta being on the western end of the range. However, in Minnesota distribution is much more restricted compared to the Cinnamon Fern. Royal Fern is found in a group of counties on the east central side of the state from Stearns on the west, Aitkin on the north and Washington on the south. Ramsay, Carver, Scott & Dakota are metro exclusions. In addition it has been found in the Arrowhead and in Goodhue. It is considered "threatened" in Iowa.

In North America there are only 4 main species of the Osmunda genus: O. cinnamomea, the Cinnamon Fern; O. claytoniana, the Interrupted Fern; O. ruggii, a sterile hybrid found only in Virginia; and O. regalis, the Royal Fern. The latter has two varieties but only one is found in North America - var. spectabilis. O. cinnamomea has had four varieties described in North America but current authorities such as Flora of North America do not distinguish them. All three main species are represented in the Garden. The hybrid in Virginia is described as - Osmunda ×ruggii R. Tryon [claytoniana × regalis].

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

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