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Ferns of the Sierra (1960) by Robert J. Rodin


Fig. 24 FRAGILE FERN (Cystopteris fragilis)
[click to enlarge]

Fig. 24 FRAGILE FERN (Cystopteris fragilis). Upper: Frond with scattered sori. On some fronds basal pinnae also have sori. Insert: Close-up of one pinna from a larger frond. Lower: From a cool, moist, shady place. This one received moisture from the spray of a waterfall.

CYSTOPTERIS

Small delicate fronds arising from a slender rhizome. Fronds bi- or tri-pinnate, slender, quite delicate Small round sori on underside of the pinnae on free veins and covered with a membranous hood-like toothed indusium attached at the inner side of the pinna and partly folded under the very young sorus. The indusium is best observed in a young frond, soon being pushed back by the enlarging sorus, later withering and somewhat deciduous so that the old sorus may appear naked.

FRAGILE FERN
Cystopteris fragilis (L.) Bernh.
(Fig. 24)

Polypodium fragile
Filix fragilis

Plants 4 to 16 inches high with bright green lanceolate fronds, variable in form. Some are pinnately to nearly bi-pinnately compound because of deeply cut lobes. In others, leaf tissue. close to the. branches of the stalk may connect most or all leaflets together on a single branchlet of a frond. Young sori black, scattered on under side of pinnae, always located over a veinlet. After spores are shed, sori appear brown.

Sometimes called Brittle Fern, because fronds break off easily. The fronds of this fern resemble our Woodsias in size and general appearance, but the Woodsias are darker green and never have black sori. Sori of the latter are in rows near the leaf margin, not scattered. This fern grows in sheltered moist places, often along stream banks or in wooded areas. This is a widely distributed fern, occurring from Newfoundland and Labrador to Alaska, scattered locations throughout the United States, in Greenland, Iceland and Eurasia.



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