Kingdom: Plantae
(unranked): Angiosperms
(unranked): Monocots
(unranked): Commelinids
Order: Poales
Family: Juncaceae
Genus: Juncus
Species: J. articulatus
Binomial name: Juncus articulatus
Common name: Joint leaf rush, more ambiguously as "Jointed Rush"

Juncus articulatus is a non-native variable, perennial rush. It is native to Eurasia and much of Canada and the United States. It is widespread and common throughout New Zealand and it grows in moist areas, such as wet sand, drains and wet pasture and it thrives in calcareous soils. It is sometimes found submerged or floating.
The usually round prostrate stems may root at nodes, and they generally have one or more cylindrical leaves up to 10 centimetres long. Horizontal internal joints may be seen or felt on the stems of the plant.
This is a perennial herb produces a mainly erect stem from a short rhizome. The inflorescence atop this stem has several branches with up to 25 clusters of up to 12 flowers each. Each individual flower has greenish to dark brown, pointed tepals 2 to 3 millimetres long, six stamens bearing anthers, and a protruding, feathery pistil. The fruit is a dark brown capsule with a pointed tip.

Juncus articulatus Joint leaf rush-003.JPG

The seed stalks are visible.
Juncus articulatus Joint leaf rush-001.JPG

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