Osmunda claytoniana Linnaeus

Interrupted fern

Etymology Named in honor of John Clayton (1686-1773), who has been described as the greatest botanist in America at that time.
Description Rhizome: erect, massive, forming a trunk, occasionally branching, hairs and old stipe bases woven together with black, fibrous roots.
Frond: 90 cm high by 20 cm wide, though sometimes taller, deciduous, dimorphic, outer ring of fronds arching, sterile, inner erect, fertile, blade/stipe ratio: 2:1.
Stipe: stipules (flared leaf base), unique to the family/genus, hairy when young, soon glabrous, vascular bundles: 1 in a U-shape where the top of the arms continue to curl.
Blade: 1-pinnate-pinnatifid, sterile fronds elliptic to oblong, arching, pinnae broadly oblong; fertile fronds with 2-7 middle pinnae pairs greatly constricted, bearing sporangia, withering soon, somewhat waxy, shedding water, reddish to light brown hairs, soon falling.
Pinnae: 20 to 30 pair, catadromous, rotated to the horizontal; margins entire, rounded apex; veins free, forked.
Sori: none, indusium: absent, sporangia: large, globose, greenish young, tan or black when mature, spores green, maturity: mid spring to early summer.
Dimensionality: fronds vertical early in the season, declining later.
Culture Habitat: woods, on hummocks in swamps, more or less neutral soil. Distribution: eastern North America, eastern Asia and Himalayas. Hardy to -35C, USDA Zone 3.
Distinctive Characteristics The central, sporangial section on fertile fronds is unique.
Osmundastrum claytonianum (L.) Tagawa
Osmunda claytoniana
Osmunda claytoniana.  Illustration by V. Fulford from Ferns and Fern Allies of Canada, William J. Cody and Donald M. Britton, 1989, © Agriculture Canada.
Osmunda claytoniana
Osmunda claytoniana.Shortly after emergence, very upright habit, Quebec in late May.
  2005 Louis-M. Landry at CalPhotos
Osmunda claytoniana
Osmunda claytoniana. Relaxed habit, Quebec in early June. Not, of course, the same plant.
  2005 Louis-M. Landry at CalPhotos
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