The segments of the pinnæ are from fifteen to twenty each side the midrib: the incisions do not extend quite to the midrib, so that the latter is narrowly winged, and the pinnæ are pinnatifid rather than pinnate. The segments are from nine to eighteen lines long, and about three lines wide: they are set rather obliquely on the midrib, and are often slightly curved upwards, or falcate. They are obtuse or somewhat acute, and have the edges crenate, or more or less distinctly serrate with sharp incurved teeth.
The veins are free, and are pinnately forked into from three to five slender oblique veinlets, of which the lowest one on the upper side is the longest, and bears a fruit-dot near its base. The fruit-dots are seldom or never found on the two or three lowest pinnæ, but on the rest they are arranged in a row each side the midveins of the segments, and much nearer the midveins than the margins. There are in all from ten to twenty to a segment.
The indusia are larger than in most of the related species, flat, perfectly smooth, orbicular with a very narrow sinus, and slightly erose-crenulate on the margin. In the second edition of Gray’s Manual it is said that the indusium is “often orbicular without a distinct sinus, as in _Polystichum_;” and it is sometimes difficult to see the sinus, but I think it is rather because the sides of it overlap than because there is none. The sporangia have a ring of from fifteen to twenty articulations. The spores are ovoid, and somewhat roughened on the surface.
This fern is one of the very finest and largest of the species of the Eastern States, being surpassed in these respects only by the osmundas and the ostrich-fern. The fronds are smooth, deep-green in color, slightly paler beneath, and of a rather firm papery texture. Unlike _A. Filix-mas_ and _A. cristatum_ the fronds wither in the fall of the year, and are not “half-evergreen.”
It was collected by Pursh on his visit to America in the early part of this century, the precise locality not known,—in the Flora he says “New Jersey to Virginia,”—and was by him referred to _A. Filix-mas_. His specimens, preserved in the herbarium at Kew, are partly _A. Goldianum_ and partly _A. cristatum_. Mr. John Goldie’s discovery was made near Montreal, about the year 1818, and the excellent figure in Hooker & Greville’s Icones Filicum was probably taken from one of his specimens, or perhaps from live plants originally brought by him to the Botanic Garden at Glasgow.