Kingdom: Plantae
(Unranked): Angiosperms
(Unranked): Monocots
(Unranked): Commelinids 
Order: Poales
Family: Cyperaceae 
Tribe: Cariceae 
Genus: Uncinia 
Species: U. Uncinia 
Scientific name: Uncinia uncinata 
Common names: Hook Sedge, Hook grass, Bastard grass, kamu, matau-a-maui.

Uncinia uncinata is native hooked sedge of New Zealand (including the Antipodes) it is also found in the Society Islands and Hawaii. Its natural habitat is from the coast up to 1000 m and is found in areas ranging from native forest to shrubland.
Uncinia uncinata forms dense mounds of orange-red, or green, arching leaves about 50 cm high. The leaves are 20–40 cm long and 4–7 mm wide. The flower stems can reach about 60 cm, the flowers form a simple spike, with male flowers on top and female flowers below.
Hook sedge is characterised by the presence of a long hook formed by an extension of the rachilla, which is used to attach the fruit to passing animals (epizoochory) and it is this feature which gives the genus its name, from the Latin uncinus, meaning a hook or barb. This causes a problem to any humans with hairy bare legs when walking through it.

Green form.
[1] 

Red form from the Ruapehu area.
[2] 

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0