Ferns of the Eloise Butler Wildflower Garden

Interrupted Fern is a vase shaped fern, to 3+ feet in height, whose shape is very similar in appearance to the Cinnamon Fern, but unlike the Cinnamon, the Interrupted Fern frond can bear both sterile and fertile pinnae (pinnae is the plural of the smaller leafy side branches that grow off the main stem - individually they are pinna, and if the pinna itself has one or more distinct secondary segments, as does this species, these are called pinnules). The fertile fronds are more erect, the sterile fronds more spreading. The frond blades are pinnate-pinnatifid.

Fronds - fertile: A fertile frond is interrupted in the middle by 2 to 5 pairs of smaller spore producing fertile pinnae that resemble brown clusters of very small grapes. These clusters are the "sporangia." These fertile pinnae, during their time on the plant, remain small and are thus interrupted in their growth. Above and below that "interruption" the pinnae are the normal yellow-green color, widest at the base, but those below the interruption are much shorter and ascending in position, more widely spaced. Fertile fronds are taller than the sterile fonds and more erect.

Fronds - Sterile: The sterile fronds are those without any fertile pinnae; they are broadest in the middle area, cut into 10 to 20 pairs of pinnae, woolly at first, then losing the hair. There is also a lack of hair at the base of the sterile pinnae underside which helps distinguish this fern from the Cinnamon Fern whose sterile fronds look similar to the sterile fronds of Interrupted Fern.

Pinnules: The pinnules become wider toward the central stalk (costa) of the pinna. The main vein of the pinna costa does not branch into the individual pinnules. The tips of pinnules are bluntly rounded and the bases are not quite cut clear to the costa of the pinna.

Fertility: The 2 to 5 pairs of smaller spore producing fertile pinnae have "sporangia" that resemble brown clusters of very small grapes. Instead of sori housing the sporangia, the fertile pinnae of this and other Osmundas have bare or "naked" sporangia on their fertile pinnae. These small brown clusters of sporangia, are light green initially, then dark green at maturity at which time they open and release their spores, then they turn dark brown after they have discharged their spores and fall off in late summer.

The fiddleheads (Croziers) are stout, with their woolly white hair, typical of Osmundas, and are some of the earliest to emerge in spring. Mature fronds are smooth and free of this hair. Croziers were once considered edible but are now known to be carcinogenic. If only Eloise Butler was aware of that! (read her note at bottom of page).

Habitat: Interrupted Fern grows in both shade and open areas. The plant prefers alkaline, drier soils, well drained, not marshy. Roots are a tangled mass of wiry black growth growing from a large rhizome.

Names: The genus Osmunda has an obscure derivation. Some believe it is named after an early Scandinavian writer Osmundus and some say it is named for Osmunder, a Saxon name for a Celtic god Thor. The species name, claytoniana, was an honorary named for the English born Virginia botanist John Clayton, (1694-1773) who lived in Williamsburg. Clayton sent plants to Europe, particularly to England and to Dutch naturalist Johann Friedrich Gronovius. Carl Linnaeus, working with Gronovius, published his first book, Syetema Naturae, and included these plants in the book. Clayton then sent to Gronovius his catalog of Virginia plants, Gronovius proposed to Linnaeus to arrange it and publish it. This became Flora Virginica,1739-43, the first book on new world material using the Linnaean system of classification. Unfortunately, Gronovius did not tell Clayton and did not have his permission. The author name for the plant classification, 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Comparison ferns: There are three that could be confusing - Royal fern (The fertile pinnae have the sori at the tips of the fertile green fronds), Cinnamon Fern (The fertile fronds are distinctively separate with the pinnae appressed to the rachis) and Ostrich Fern (fertile frond is also distinctively separate but the fertile pinnae arch outward from the rachis, not appressed like the Cinnamon).