Osmundastrum cinnamomeum

Osmundastrum cinnamomeum (L.) C. Presl
(from Latin: cinnamum, which was from Greek: cinnamon kinnamomon, and apparently ultimately from Hebrew/Phoenician: kinamon or qinamon, possibly meaning Chinese amomum or spice, China being from where it was thought to have come—Bashalon 2008; in reference to the bark of Cinnamomum verum (Lauraceae), source of the spice cinnamon, meaning cinnamon-colored or cinnamon-brown, a lightish brown mixed with yellow and red; in this species in reference to the color of the hairs on the young petioles, rachis, and pinnae, these usually persisting into maturity only as a tuft at base of pinnae)

Local names: cinnamon fern, buckhorn fern, buckhorn brake, flowering fern

Leaves dimorphic, erect to spreading, in a vase-shaped cluster from a stout, woody, creeping rhizome; petiole straw-colored to greenish, with hairs when young; sterile leaves 1-pinnate-pinnatifid, ca. 0.3–1.5(–2) m long, the smallest subdivisions with margins entire and usually apically mucronate; pinnae with a persistent tuft of usually cinnamon-colored tomentum on abaxial surface at base; rachis greenish, with hairs when young; fertile leaves strikingly different, not very leaf-like, with no expanded pinnae, densely tomentose, much narrower and shorter than sterile leaves; sori absent, the sporangia clustered, cinnamon-colored; 2n = 44 (Whetstone & Atkinson 1993). Wet areas; Pineywoods and Gulf Prairies and Marshes w to Leon (BAYLU), Milam (Correll 1956; Turner et al. 2003), Lee (BRIT), Henderson, and Van Zandt (Turner et al. 2003) cos. in the Post Oak Savannah and to Lamar Co. (BRIT) in Red River drainage; also disjunct sw to Gonzales Co. (Parks & Cory 5630, 5634, TAES; Tharp s.n. 1935, TEX-LL;) and to Uvalde (Turner et al. 2003) Co. on the Edwards Plateau; se Canada and throughout e U.S. w to MN and TX; also s Mexico and s to South America and Asia. Sporulating Mar–Jul or later. [Osmunda cinnamomea L.] This is one of the most interesting TX ferns from the standpoints of biogeography (= scientific study of the geographic distribution of organisms) and evolution. Within TX, cinnamon fern is widespread in the Pineywoods of East TX and parts of the adjacent Post Oak Savannah; isolated populations are also disjunct sw to Gonzales Co. in the s Blackland Prairie and even farther to the w to Uvalde Co. in the w Edwards Plateau. The occurrence in Gonzales Co. is in the Ottine wetlands—a unique, isolated, spring-fed, relict wetland ecosystem on the floodplain of the San Marcos River. Cinnamon fern and a number of other species disjunct to the Ottine wetlands are relicts of more humid conditions in the past. Because of unique hydrological circumstances, they have been able to survive since Ice Age times in a tiny island of appropriate habitat surrounded by a sea of now inhospitable environment. The present occurrence of cinnamon fern in the Ottine wetlands is not too surprising, since peat cores from the area dated to the Pleistocene contain cinnamon fern spores (see page 36 for discussion of this disjunction). Its broader modern distribution, North America to South America and disjunct to Asia, is also interesting, suggesting an ancient origin and a much more widespread range in the past (Kato & Iwatsuki 1983) (see page 33 for a discussion of such distributions). Recent fossil discoveries from the Upper Cretaceous (Serbet & Rothwell 1999) of w North America provide evidence that O. cinnamomeum was more widespread in the past, that it has been in North America “for at least 70 million years.” and suggest that fern species can remain virtually unchanged over millions of years (an example of evolutionary stasis). Further, this would mean O. cinnamomeum has the greatest known longevity of any individual vascular plant species. Based on the longevity of this and other ferns, Rothwell and Stockey (2008) suggest that there is a “a dramatically different mode and tempo of evolution for some homosporous plants than for seed plants.” Old and New World populations of cinnamon fern have apparently been separated for a very long time (Yatabe et al. 1999 estimated 25–35 million years) and their relationships are unclear. Metzgar et al. (2008) wrote that, “Because they are clearly distinct based on nucleotide data, it is possible that New World and Asian individuals of O. cinnamomeum represent distinct species, as suggested by Yatabe et al. (1999).” Further study will be needed to determine the appropriate taxonomic rank for these widely separated populations. Cinnamon fern can be confused when sterile with the superficially similar, but only very distantly related Woodwardia virginica, virginia chain fern, in the Blechnaeae. However, as noted by Weakley (2010), cinnamon fern “is coarser (to 2 m tall, vs. to 1 m tall), has cinnamon tufts of tomentum present in the axils of the pinnae (vs. absent), has the rachis greenish and rather fleshy in texture (vs. brown and wiry), and bears fronds clumped or tufted from a massive, woody, ascending rhizome covered with old petiole bases (vs. fronds borne scattered along a thick, horizontal, creeping rhizome).” When fertile, the two species appear dramatically different (in Woodwardia virginica the fertile pinnae are essentially like the sterile).

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