Cyathea alderwereltii is a species of tree fern endemic to Mount Sago in central Sumatra, where it is nevertheless abundant and grows in forest at an altitude of 1000-1500 m. It has an erect trunch which may be 4 m tall or more. Fronds are bi- or tripinnate and 1-2 m long. The stipe of this species is spiny at the base and covered with scattered scales that are dark brown, glossy, and have a narrow paler margin. Sori are produced near the fertile pinnule midvein and are covered by small, brown scale-like indusia.