Which preposition to use with triodia

in Occurrences 3%

In many places we began to observe patches of triodia in the midst of the alluvial plains through which the river continued to run, and distant ranges were observed both to the north and south.

on Occurrences 1%

The valley of the river is now more open, but the country of very barren character, with stunted eucalypti and triodia on the hills, and melaleuca and flooded-gum trees, with a little grass, on the bank of the river.

Which preposition to use with  triodia