Docks can be troublesome weeds of cultivation and curled dock (Rumex crispus) along with its close cousin broad-leaved dock are as guilty as any! Both are very common and can spread over quite large areas if unchecked. The two also hybridise and they happily live together.
Telling curled and broad-leaved dock apart is relatively easy just by the leaved. Curled dock has narrow leaves that, yes, 'curl' up around the edges whereas broad-leaved dock has, yes, broad leaves that are mainly flat. The flowers are a little different too with curled dock flowers being redder and in bigger clusters. Once the hybrid species kicks in it becomes much more difficult.
Curled dock contains oxalic acid and a high iron content. It is used for a variety of herbal remedies including the treatment of anaemia. The leaves are also used as a form of cabbage in some places but they have to be boiled for some time with frequent changes of water to remove the unwanted chemicals.