March 2020 Update: A new review of the U. dichtoma complex (Jobson 2020) has been published so the information in this article might not reflect the current taxonomy, especially at the subspecies level. Read the paper here.
The purple flowered species of the Utricularia dichotoma complex have long been confused. Over the years, taxa have been elevated from and reduced back to the dichotoma species complex rather frequently. Often the species are quite superficially similar and can be distinguised by small details such as the number of bumps on the lower petal and the shape of the bracteoles. Here’s some images of some of these species I’ve seen and a discussion of their morphological traits.
Utricularia dichotoma
Utricularia dichotoma has a wide distribution from Queensland, down the east coast to Tasmania and New Zealand. The species can be found in wet niches such as swamps or on the edges of small creeks.
The bracteoles of the species 
Plants often have two concurrent blooms 
The species has distinctive scale shaped leaves. Oftentimes, growth can be submerged 
The flowers are generally vivid purple. Three raised yellow ridges adorn the lower petal in a triangular pattern.
Utricularia grampiana
Utricularia grampiana is endemic to the Grampians area in western Victoria. The species grows during the cooler months and blooms during spring and summer, until the water dries out. In contrast to U. dichotoma, this species prefers to grow in moss on moist rock faces and ledges.
U grampiana blooming en-mass on a shaded cliff face 
Lateral view of the species showing the bracteoles 
The plants also grow in exposed areas on moist rock ledges 
The species is usually single-flowered. The two yellow ridges on the lower petal are prominent and raised.
Utricularia barkeri
Utricularia barkeri is native to Victoria and South Australia. I have not observed this species enough to suggest how it usually grows in the wild. The one population I saw grew on an exposed seepage on the side of a walking trail in coastal heath.
Front view of a flower 
The bracteoles of the species 
Lateral view of a flower 
Compared to U. dichotoma, the lower petal of U. barkeri has a broader outwards flare.
Utricularia uniflora
Utricularia uniflora is commonly found in the south eastern states of Australia. The species never grows submerged, preferring the mossy margins of creeks and on moist rock faces. The flowers vary widely in colour, ranging from white to pink to vivid purple. The leaves are very small and resemble circular scales.
A typical specimen. The edges of the lower petal are usually flared slightly upwards. 
A lighter coloured specimen 
The species grows in wet mossy surfaces out of standing water 
Two raised yellow ridges are surrounded either side by a sharply raised white ridge on the lower petal.
Utricularia aff. dichtoma – Maddens Plains
There are plenty of populations that don’t quite fit the archetypal description of the published species. In the Maddens Plains area south of Sydney, a purple flowered Utricularia exists that resembles U. dichotoma but has some notable differences. This species grows in the wet edges of creeks and can grow into the water. The emersed leaves do not resemble those of the standard dichotoma in that they are small and thin.
Laterial view of the bloo showing the bracteole 
A grouping of flowers 
Emmersed leaves of the plant 
A front view of the flower
