Forming an understorey to the sedgeland.
Marsilea drummondii is suggested because: of the size of the fronds - the largest were 2-3 cm in diameter (no other species gets this large): and having an upper surface glabrous and lower surface hairy is known (described in Flora Vic).
It is certainly not mutica (lacks the distinct coloration of mutica), and not costulifera (lacks the awkward wedge-shape of costulifera).