Sea Arrowgrass Sea Arrowgrass Sea Arrowgrass Marsh Arrowgrass

What are they?

The arrowgrasses are unusual plants, looking a little like a number of other groups, such as rushes or irises (in their leaves) or plantains (in their flowers), but never quite matching any of them and more a mixture of them all! They have creeping root systems and the leaves are mostly in a basal rosette, linear and slightly fleshy. The flowers appear in long narrow, spikes, each flower having six, greenish 'tepals' and revealing the plants to be monocotyledons - most closely related to the pondweeds and similar waterplants.

Where are they found?

These are plants of wetlands, with Marsh Arrowgrass favouring freshwater habitats while Sea Arrowgrass favours coastal saltmarshes.


The combination of basal, linear, fleshy leaves and a spike of six-tepalled flowers separates these plants from all others in our region. Habitat helps to tell the two species apart, but some plants can be difficult and the species comments below should be read carefully. In saltmarshes, Sea Arrowgrass grows with Sea Plantain and the two can look similar, but Sea Plantain has flatter leaves that are slightly fleshy but not semi-cylindrical in cross-section.

Marsh Arrowgrass      Triglochin palustris

Native. Widespread in wet grassland, marshes and flushes in river corridors, although missing from many of the region's wetlands. Favours freshwater habitats, but also occurs at the fresher end of saltmarshes, where the two arrowgrass species may be found growing together. Flowers July to August. Typically a small plant (to 50cm in height but often much less), to the point where it may be very easily missed amongst other vegetation, even when in flower. The leaves are often grooved on the upper side, near the base and the seed capsules lay flat against the main stem as they ripen.

Marsh Arrowgrass Marsh Arrowgrass Marsh Arrowgrass
Seed capsules

Sea Arrowgrass      Triglochin maritima

Native. Common in coastal habitats, especially saltmarsh but also shingle beaches and salty mud along roadsides and disturbed locations. Flowers July to September. A low plant (to 60cm in height) but typically larger, more leafy and more robust than Marsh Arrowgrass. The leaves are usually flat, not grooved on the upper side, near the base and the seed capsules are held away from the main stem as they ripen.

Sea Arrowgrass Sea Arrowgrass Sea Arrowgrass Sea Arrowgrass
Leaf cross-section
Seed capsules