Urtica dioica; I hesitated to put a page of this plant on the Natural History of Iceland site. The reason is that the Common Nettle is not a natural element but an introduced alien only to be found on waste sites near human settlements. This plant often invokes negative feelings because of its stinging qualities. Having said this though, it has excellent qualities for man-kind. One can make delicious soups from young shoots and can help patients suffering blood loss (it contains quite a bit of iron, but to be honest parsley is even better).
So it is not a common plant on Iceland but can nevertheless be found regularly around human settlements. A close relative is the Small Nettle (Urtica urens). This species is an annual generally growing on arable fields and gardens that are regularly hoed. It has the same stinging feature as the Common Nettle. It can be distinguished by the more rounded leaves and the bisexual flowers (The Common Nettle has either male or female flowers, hence the name "dioica"). The Small Nettle usually appears as a single plant with many side shoots whereas the Common Nettle forms many dense single-stem shoots from rhizomes (root runners), quickly covering many square meters.
It is a member of the Nettle Family (Urticaceae). The Icelandic name of this species is Brenninetla.