Note the frilly margin of the labellum which is square and notched at the apex.(Distinguishes it from Microtis parviflora which has a non-frilly labellum that tapers to a point without the notch - triangular-shaped.)
Update: Close-up photos showing labellum detail added.
Note the variation in the shape/notching of the labellum. Some flowers only have minute notching on a square-ended labellum. Others have two rounded lobes with one shallow notch between them **but there is no gap or "decurved point" between the lobes**.
That makes it M. unifolia, I think, even though a proportion of the flowers have a bilobed labellum.
Looking at photos elsewhere, it seems that the id feature "labellum pendulous - not pressed against ovary" can be seen in both arenaria and unifolia.
New species record for this collection. Found in the area burnt in last year's January wildfire. Large sheathing bracteole visible in second pic. As a result of this observation and analysis of herbarium samples, the VicFlora entry was updated to include "Leaves (with) margins, at least toward base, usually with irregularly spaced, small tooth-like outgrowths."
New species record for this collection. Found in the area burnt in last year's January wildfire. This record is possibly an example of cleistogamy or apomixis in this species, with many plants flowering at this time too.