how to distinguish the 2 species? in 2005 we found Diuris sp further south which looked similar to, but didn't fit entirely D pardina - I thought it might be a hybrid. Unfortunately, the camera I used at that time doesn't have coordinates embedded; I know roughly the site and can upload the historic photos. I checked over the years but never spotted them again - perhaps because of massive overgrazing.
Not easy I think! I don't think the precise differences are well sorted, but pardina typically has darker blackish markings on flowers and more brown/blackish markings on lateral petals (ears). In general you get pardina on Majura/Ainslie and nigromontana on Black Mtn. To me nigromontana has a somewhat rounder flower/labellum shape but not sure how consistent this is.
Hmmm , hopefully the plant Taxonomists can improve on this rather subjective morphological differentiation. What would be much more reliable is to look at Genetic footprints to see whether there are Actually (2) different species ? or whether these are just localised variations / phenotypic Diversity, which we would expect for any species population.