Triglochin maritima / seaside arrowgrass

Adjectives: clonal, emergent aquatic, fen, interesting bits, native, toxic, wet meadows, winter botany

Also known as:  common arrowgrass, sea arrowgrass, shore arrowgrass, Triglochin
Synonym: Triglochin concinna, T. elata

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Despite the name, T. maritima is found in every state and Canadian province except those in the southeast, and is otherwise circumboreal (i.e. around the world in the north). Actually, it is also found in South America, so not just the north. I suppose it was first named by Linneas who knew it from the sea coast, and in Britain, for example, it is very rare except on the coasts. It is certainly extremely tolerant of salinity and doesn’t have salt glands or any way to get rid of salt once it is taken in. But… it clearly doesn’t need that. In the Valley, I have most often seen it in the low, boggy fens or along roadsides through them.

There is one other species possible in Idaho, T. palustris (marsh arrow grass), but it tends to be less “fleshy” and to have the individual flowers more widely spaced on the stem (spike or raceme). It is nowhere near as common.

Seaside arrowgrass is a perennial and grows as a tuft of stems from a stout rhizome. It propagates both by seed and clonally.

Mostly if you see this species, you will recognize it by the gross morphology of the flowering stalks. They are tall and straight, although occasionally you may see on with weird twists and turns and bends. The flowers are greenish, 6 tepaled (petals and sepals are all similar) and edged with purple. The stigmas are hair-like, purple and make up a cute feathery cluster. They are globular and only about 1/8 inch long, i.e. much too teeny to see any of their beauty without a hand lens.So what you will see is the inflorescence, each spike having many flowers (like, over 100). Unlike many species with raceme/spike inflorescences, those of Triglochin don’t elongate much once the flowers begin to open.

Triglochin fruit are green and cylindrical, about 1/8 inch long, and very gradually turn brown. Each fruit has six seeds. Since they stay on the spike for a long time, these are another very recognizable feature of the plant.

Triglochin leaves are mostly basal and erect in the manner that grass leaves are. They are dark-ish green and smooth – no hairs or teeth. They can be up to 16 inches long but no matter how long, the flowering stems extend well above them. They are more or less semi-circular in cross section with a groove down the upper side.

Interesting bits – Experiments in salt marshes in New England have shown that arrow-grass is an “ecosystem engineer”. Basically, it has a dense root mat that creates a spot with elevated soil that other plants can colonize. This enhances the overall plant diversity of the marshes as well as providing another habitat for arthropods or other small animals. The more Triglochin is flooded, i.e. waterlogged, the more fine shallow roots it makes. I think this feature must be the only reason that you can actually buy T. maritima seeds from companies specializing in conservation and restoration. Otherwise, it is noteworthy that the leaves produce various cyanogenic (cyanide producing) compounds and are seriously toxic, especially when young.

Another interesting bit is that T. maritima occurs with a large number of different ploidy levels. A huge range of 2n chromosome numbers has been found, e.g. 12, 24, 30, 36, 48, 60, 120, 144.