Blechnum keysseri Rosenst.

Rhizome short, semi-erect, erect or rarely scandent, 1 cm diam., densely clothed at the apex with scales which are ovate acuminate, 0.4-1 by 0.1-0.3 cm, entire, shiny, reddish brown sometimes with slightly paler margins. Fronds dimorphic, sterile and fertile fronds 15-100 cm or more in length, 5-28 cm wide; the fertile lamina sometimes smaller than the sterile, but with a longer and more fully pigmented stipe and rhachis; fertile fronds often smaller than sterile and with more fully pigmented stipe and rhachis. Stipes 4-20 cm, pigmented purplish black to dark reddish brown, usually on the abaxial face, groove of upper surface of stipe paler, scales at the base similar to those of the rhizome but usually shorter, sometimes surface near the base densely covered with short, fine, reddish brown, multicellular uniseriate hairs which when shed leave a papillose surface, otherwise glabrous and smooth. Lamina narrowly elliptic to ovate, the sterile deeply pinnatisect for most of its length becoming pinnate towards the base and pinnatifid at the apex, 7-30 pairs of pinnae plus 0-15 reduced lobes at the base, the sterile lamina usually ⅔ the length of the frond; the fertile lamina often only half the length of the frond. Rhachis and costae pigmented on the abaxial face up to almost the length of the rhachis and the costae, otherwise pale stramineous, sometimes very short fine reddish brown hairs present but more often glabrous. Sterile pinnae long narrowly elliptic, slightly to distinctly falcate, acuminate, 6-16 by 0.8-2.5 cm, adnate, contiguous, coriaceous, margins entire, slightly thickened, narrowly revolute, undulate at apices, pinnae dark green on upper surface, mid-green to very pale almost white on lower surface, veins immersed, simple or often several times furcate and terminating submarginally in round glands, basal pinnae shorter then abruptly reduced to very short vestigial auriculate lobes, often only 0.2-0.3 cm (or less) long and 1.5 cm broad, contiguous or several cm distant, terminal pinna broader and sometimes larger than the lateral pinnae of the mid-region and may be pinnatifid at its base. Fertile pinnae narrow linear acuminate, 5-20 by 0.15-0.45 cm, sori continuous and occupying under­surface except for c. 1 cm at the pinnae apices, adnate and decurrent at the rhachis, basal pinnae shorter then steeply reduced to aborted lobes or minute vestigial outgrowths, usually sterile, increasingly distant and similar to at the base of the sterile lamina. Spores 43.2 by 34.7 µm (from 13 herbarium specimens), perine smooth, scabrous, microrugulose or with some reticulation, exine smooth.