This species usually has a single subterranean stem with an exposed apex. Unlike E. villosus, E. aplanatus does not sucker. It usually produces 2 to 8 erect, arching leaves up to 3.5 m long which sag horizontally with age. Leaves have a petiole up to 200 mm long. The lower rachis is covered with a whitish indumentum. Mature leaves are dark green and glossy, the leaflets twisted and undulating. The leaflets are directed towards the apex, and opposing leaflets are at 180 degrees to each other. Lower, proximal leaflets progressively decrease in size, finally reduced to prickles. Median pinnae are up to 300 mm long, 40 mm wide, narrowly ovate, tapering to an acute tip with both margins sparsely dentate, very rarely entire.

Male plants produce up to three cones, green when young, turning yellow when mature, up to 650 mm long and 80 to 100 mm in diameter, with a peduncle up to 220 mm long. Pollen is shed from the smooth, hairless microsporophylls in mid autumn.

Female plants produce one to two cones up to 400 mm long and 120 mm in diameter. Peduncles are short and stout and up to 60 mm long. The exposed faces of the megasporophylls are flat, smooth and hairless, with indistinct facets armed with sharp abaxial ridges. Female cones appear in mid-summer (January) and disintegrate in early to mid-spring. Seeds are ellipsoid, about 25 mm long and 13 mm to 15 mm in diameter. The sarcotesta is bright red.