Juncus gerardii

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Juncus gerardii (blackgrass, black needle rush, or saltmarsh rush) is a perennial plant in the rush family Juncaceae. It grows in loose clumps from a dense network of dark underground stems (rhizomes). Stems are slender and 25–75 cm tall. Leaves are narrow and channelled. Flowers appear near the ends of the branches, with a short bract. The petals are dark brown and surround black seed capsules, which can give the capsules a striped look.

Habitat and range
Juncus gerardii lives on coastal sites and intertidal zones, in salt marshes, wetland margins, disturbed areas, and wastelands. It tends to settle just above the high-tide line, preferring salty, waterlogged soils, but it does not tolerate long flooding.

It is native to Europe (from the Mediterranean to Mongolia) and North America. In North America, it has spread to places like the Great Lakes region, where it can threaten native plants and may help spread certain insects that carry diseases. It has been introduced to Greenland, New Zealand, Australia (Tasmania and Victoria), and parts of Asia.

In New Zealand, it arrived by accident and became naturalised in 1891. It is considered invasive there, forming large stands that crowd out native vegetation and reduce grazing.

Reproduction
Juncus gerardii mainly spreads through creeping rhizomes to form clonal patches, but it also flowers from late spring to summer and produces seeds.