Subgenus: Sphaeropteris
Species:C. medullaris
Binomial name: Cyathea medullaris
Common name: Black tree fern, Mamaku

Mamaku tree ferns grow in damp gullies throughout New Zealand. Reaching 20 metres in height, they have oval-shaped frond scars on the trunk. The white pith of the trunk and the koru (new shoots) are edible, although slimy when first cut. Maori stripped the trunk’s outer layers so the slime could dry or drain away. The plant was then cut down and cooked whole. Alternatively, koru (new shoots) were hung to dry. Baking was the preferred way to cook mamaku, to separate the stringy fibres from the flesh. Although the taste is bland, the nutritional value is high.

Cyathea medullaris Black tree fern Mamaku.JPG

[ Cyathea medullaris Black tree fern Mamaku.JPG
Fronds are up to 5 m in length and arch upward from the crown of the plant.
Cyathea medullaris. Black tree fern-1.JPG

Young frond, rachis and stipe - The axis (rachis) and stipe (stalk) of the young frond has a dense covering of scales which drop away as the frond expands. 

Topside of a frond. The frond axis (rachis) bears a series of leaflets (pinnae) left and right.
Each of these is further divided into smaller leaflets so that the frond is 3-pinnate.
Cyathea medullaris Black tree fern.JPG

The underside of a sterile frond
Cyathea medullaris Black tree fern-001.JPG

The underside of a fertile frond
Cyathea medullaris Black tree fern-002.JPG

Leaflet, scales 
Small, 0.5-1.5 mm long, scales with spiny margins are found on the lower surface of the frond leaflets.
Cyathea medullaris black fern underfrond.jpg

A damaged frond will 'wept' sap for days afterwards trying to heal its self. 
Cyathea medullaris oozing sap Black tree fern Mamaku.JPG

Thanks to Wikipedia for text and information: