Eleocharis palustris; The Common Spike-rush is the largest of all Icelandic Spike-rushes. It more than 20 cm tall, sometimes as tall as 70 cm. Spike-rushes typically have an inflorescence on top of a round stem usually - but not always - without leaves. They grow in very wet conditions, often emerging out of shallow water. To tell the different species apart follow this key:
Eleocharis palustris - Common Spike-rush: It is the largest spike-rush (20 to 70 cm tall)
Eleocharis uniglumis - Slender Spike-rush: very similar to E. palustris. It is slightly smaller but the defining characteristic is the first bract under the infloresence. It completely encircles the stem whereas this bract in E. palustris only encircles the stem only halfway.
Eleocharis acicularis - Needle Spike-rush: A very small species no more than 5 cm tall. Also, unlike many other spike-rushes it has grass-like leaves on the base of the plant.
Eleocharis quinqueflora - Few-flowered Spike-rush: about 15 cm tall. It has a small few-flowered inflorecence
Trichophorum cespitosum - Deergrass: Also about 15 cm tall. Characteristically this plant has very small leaf-like appendages on the stem sheaths (no foto(s) yet).
It is a member of the sedge family (Cyperaceae). The Icelandic name of this species is Vatnsál.