Shape: Brittle Bladder Fern is an erect to arching, clump forming fern with delicate fronds rising from 4 to to 10 inches long.
Fronds - Fronds are either in sterile form or fertile form with the shorter sterile fronds appearing first in Spring. The blades are lanceolate (widest just below the middle), up to 3 inches wide, There are no aromatic glands. Fronds are produced throughout the growing season but they may die back is a dry summer, but will re-emerge with moisture. Sterile fronds look the same except shorter. Blades are light green to dark green, and vary from bi-pinnate - pinnatifid to tri-pinnate from. The stipe is short, smooth, green to straw color, usually darker near the base, sometimes with a few scales and is brittle near the base.
Pinnae: The pinnae are lance shaped, usually 12 pairs, perpendicular to the rachis, opposite each other, or sub-opposite, and not curving toward the tip of the blade. The lower pinnae are widely spaced.
Pinnules: The lower pinnae will be cut into pinnules that have either lobed or toothed margins and truncate to obtuse at the base. Upper pinnules may be entire. Pinnule veins will end at the margin if toothed.
Fertility: The sori are placed on the back of the pinnule on a vein and widely spaced. Sori are rounded with a thin, ovate shaped indusia covering them, but open on the side facing the pinnule tip, like a pocket or bladder, and without glands.
Habitat: Brittle Bladder Fern grows in clumps or cluster from a creeping rhizome. Fronds emerge from the tip of the rhizome. It is found in rocky woodland soils, on ledges and cliffs. With adequate moisture it will be green all Summer. New fronds emerge all season.
Names: The genus Cystopteris is derived from two Greek words - kystis, meaning a 'bladder' and pteris, meaning 'fern', in particular a fern with certain type of indusium. The species fragilis means 'fragile' referring to the brittle stipe. The author names for the plant classification are: First to classify was '(L.)' which is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was amended by ‘Bernh.’ who is for Johann Jakob Bernhardi (1774-1850) German botanist, Professor of Botany, director of the Botanical Garden at Erfurt. His herbarium collection is now in the Missouri Botanical Garden Herbarium.
At one time this species was subdivided into three varieties but those are no longer recognized. The older species Cystopteris dickieana has been folded into C. fragilis also.
Comparison ferns: Brittle Bladder Fern is similar to C. bulbifera, the Bulblet Bladder Fern, but that species has bulblets forming on the back of some pinnules, the blade is longer and it has glandular hair both on the rachis and the indusia. Brittle Bladder Fern also hybridizes with several other species such as C. tenuis, Mackay's Fragile Fern, which is also found in Minnesota and in some of the same counties. C. tenuis has pinnae that angle upward toward the tip of the blade rather than be perpendicular, and pinnule margins have more rounded lobes.
Above: 1st photo - The shape of Brittle Bladder Fern frond. 2nd photo - Drawing courtesy Kurt Stüber's Online Library.
Below: The lower pinnae have fully separated pinnules with toothed to rounded lobes.
Below: Two views at different times of the indusiums scattered on the veins of the pinnules. In the second photo, as the sori mature, the indusium peels back is severly degraded.
Below: 1st photo - the stipe is brittle and has only a few scales. 2nd photo - the rachis is grooved on the upper side.
Notes: Brittle Bladder Fern is not indigenous to the Garden, but introduced by Eloise Butler in 1910 with plants sourced from Excelsior Springs, MO. She planted also in 1911, '13, '18, '19(2x), and '27. Martha Crone planted the species in 1934, '35, '37, '53, and 33 of them in 1956 when she developed the Fern Glen. Her 1934 planting was 15 ferns from Chisago County, MN and the 1956 group came from Orchid Gardens in Grand Rapids, Mn.
The species eventually died out and is not known to have been replanted. Brittle Fern is a widespread species, found throughout North America except the SE section of the U.S. In dry areas it is found in higher elevations. Within Minnesota, it is found in the NE section of the state and then in scattered counties around the state but usually absent in the western section of the state and the far southern counties.
In North America there are 9 species of the Cystopteris genus, six of which are found in Minnesota.
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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"