The fertile fronds are not very common, and a young botanist may search in vain for them for a long time. They stand only about half as high as the sterile fronds, and are very rigid. They are nearly black in color: in winter they dry up, but remain erect through the next summer, so that a fruiting plant often has fertile fronds standing of two years’ growth. The frond is only a few (usually four to six) inches long, and consists of from four to ten pairs of appressed fleshy or cartilaginous pinnæ, which are divided into a double row of sub-globose bead-like segments or pinnules; the whole looking like a small and narrow but dense cluster of diminutive grapes. Each pinnule has its edges so much recurved that the whole forms a sort of pouch, apparently filled with sporangia.
Mr. Faxon has made a careful study of the sori, and has very kindly furnished the account given below.[5]
The articulations of the sporangia are said by Fée to be twenty-eight to thirty-two, and more numerous than in any other fern. I have counted only thirty at most, and more frequently only twenty-eight. The spores are ovoid and very dark-colored.
Var. obtusilobata, Torrey, Fl. New York, ii., p. 499, t. clx (Onoclea obtusilobata, Schkuhr), is not a permanent variation of the species, but is based on a not infrequent condition of the plant, in which the pinnæ of some of the foliaceous fronds become deeply pinnatifid into obovate segments, which have mostly free veins and imperfectly developed sori. The indusia appear as little whitish scales on the back of the veins. It occurs in almost all places where the plant is common, is often produced from root-stocks which bear also normal fronds, and presents all gradations from the usual sterile frond to the proper fertile one. Ragiopteris onocleoides of Presl is founded on a young fertile frond of this species placed with a sterile one of what Milde judges to be a monstrous form of Aspidium Filix-mas. Maximowicz describes a var. interrupta, from the Amoor region, in which the fertile frond nearly equals the sterile, and has elongated pinnæ, with remote segments. This condition is also sometimes seen in American specimens, and is hardly a true variety.
In an article on “The late Extinct Floras of North America,” which appeared in Vol. ix of the Annals of the New York Lyceum of Natural History, in April, 1868, Professor Newberry describes certain fossil specimens of ferns occurring in Miocene argillaceous limestone at Fort Union, Dacotah, and refers them with little hesitation to this species. I have not seen the specimens, but, as similar venation and not very dissimilar fronds are seen in Woodwardia and Pteris, one may perhaps doubt the absolute certainty of the identification.
Footnotes
[1]Milde indicates several other unimportant variations; and Hooker & Baker have as varieties of this species the East Indian Aspidium cochleatum, and Aspidium elongatum, from Madeira and the Canary Islands. The latter they give as occurring also in the southern United States, evidently supposing it to be the long-lost A. Ludovicianum of Kunze. For abundant synonymy of Aspidium Filix-mas the student is referred especially to the works of Hooker, Milde, Mettenius and Moore, as quoted above.
[2]See the “Flora of New York” for some figures of laciniated and forking fronds.
[3]Prof. Amos Eaton, grandfather of the present writer. Eaton’s “Manual of Botany” went through eight editions from 1817 to 1841.
[4]I find one or two instances of a slight enlargement of the apex, as if there were an attempt to form a proliferous bud.