Learn Icelandic: Við steininn vex falleg vatnaplanta. - Next to the stone grows a beautiful water plant.

If this sentence had standard word order, we would need the dummy subject það to fill the first slot, forming Það vex falleg vatnaplanta við steininn (There grows a beautiful water plant next to the stone). But because the location Við steininn was moved to the front, the verb vex takes the second position. In Icelandic, when an inverted clause pushes the verb into the second slot like this, the dummy það is simply dropped.

What is the grammatical subject of this sentence, and why is it at the end?

The subject is falleg vatnaplanta. Because Icelandic enforces a strict verb-second (V2) rule, putting the prepositional phrase Við steininn in the first position forces the verb vex into the second position. This causes the subject to be inverted and pushed immediately after the verb.

Why does við trigger the accusative case in steininn here instead of the dative?

The preposition við governs the accusative case when it describes physical proximity, meaning by or next to. It only takes the dative case in a few specific abstract contexts, such as describing a reaction to something or being engaged in a task, so for a simple physical location, you will almost always use the accusative.

Why is the compound word for water plant vatnaplanta instead of vatnsplanta or vatnplanta?