Cyathea is a genus of tree ferns, the type genus of the fern order Cyatheales. They are mostly terrestrial ferns, usually with a single tall stem. Rarely, the trunk may be branched or creeping. Many species also develop a fibrous mass of roots at the base of the trunk. The genus has a pantropical distribution, with over 470 species. They grow in habitats ranging from tropical rain forests to temperate woodlands. The genus name Cyathea is derived from the Greek kyatheion, meaning “little cup”, and refers to the cup-shaped sori on the underside of the fronds.

Cyathea medullaris, synonym Sphaeropteris medullaris, commonly known as Mamaku or Black Tree Fern, is a large tree fern up to 20 m tall. It is distributed across the south-west Pacific from Fiji to Pitcairn Island. The trunk is black and covered with distinctive hexagonal stipe bases. The fronds may be up to 5 m long, and arch upwards from the crown. Dead fronds are shed except in very young plants.