Osmunda cinnamomea Linnaeus

Cinnamon fern

Etymology Cinnamomea means cinnamon color.
Description Rhizome: erect, massive, forming a trunk, occasionally branching, hairs and old stipe bases woven together with black, fibrous roots.
Frond: 110 cm high by 30 cm wide, deciduous, dimorphic, outer ring of fronds longer, arching, sterile, inner fronds erect, fertile, earlier, blade/stipe ratio: 3:1 for sterile fronds.
Stipe: stipules (flared leaf base), unique to the family/genus, rusty wooly hairs 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 pinnae pairs greatly constricted, bearing sporangia, withering soon, somewhat waxy, shedding water, tuft of reddish hairs at the pinna base persistent for a while, rusty wool on pinnae and rachis soon falling.
Pinnae: 20 to 25 pair, catadromous, rotated to the horizontal; pinnules oblong, obtuse; costae costaee and rachis shallowly grooved above; margins entire; veins free, forked.
Sori: none, indusium: absent, sporangia: large, globose, greenish young, tan or black when mature, spores green, maturity: mid to late spring.
Culture Habitat: stream banks, bog, swamps, acidic habitats. Distribution: eastern North America and eastern Asia. Hardy to -35C, USDA Zone 3.
Distinctive Characteristics The tuft of hairs at the base of the sterile pinnae distinguishes this fern from O. claytoniana when fertile fronds are absent.
Osmundastrum cinnamomeum (L.) C. Presl see notes
Osmunda cinnamomea L. var. fokiensis Copel.
Osmundastrum cinnamomeum (L.) C. Presl var. fokiense (Copel.) Tagawa
Osmunda cinnamomea L. var. asiatica Fernald
Osmunda asiatica (Fernald) Ohwi

Osmunda cinnamomea
Osmunda cinnamomea.  Robbin Moran
Fossil record O. cinnamomea is thought to be the most ancient of all the living ferns based upon DNA analysis: Y.Yanabe, et al., J. Plant Res. 112: 397-404, 1999.
ssp. asiatica The Flora of Japan describes a smaller plant, sometimes called this, sometimes considered the same. The synonyms listed came by way of struggle with the Asian variety.
Taxonomy Osmundastrum cinnamomeum is now accepted. Genetic and morphological evidence places the species  far away from the other Osmunda.
Osmunda cinnamomea
Osmunda cinnamomea. August remains of wooly tuft at pinna base; earlier it is more evident. When fertile fronds are absent, this distinguishes it from O. claytoniana.  Scan: Tom Stuart
Osmunda cinnamomea
Osmunda cinnamomea. a) fertile, b) sterile fronds, c) sporangia.  Illustration by V. Fulford from Ferns and Fern Allies of Canada, William J. Cody and Donald M. Britton, 1989, Agriculture Canada.

Osmunda cinnamomea. One fertile frond at the center of the rosette of sterile fronds.  Photo Shirley Denton, from her web site, with permission.
Osmunda cinnamomea
Osmunda cinnamomea. Early on the tufts of hair at the base of each pinna are quite distinct; later in the season, as above, one has to look more closely.  Scan, Tom Stuart
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