A good discussion on current (unpublished) knowledge of Fistulina can be found under this observation: https://inaturalist.ala.org.au/observations/112243045

I spend a lot of time on iNaturalist changing identifications of Robust Bracket (Fomitiporia robusta). It seems many people think any perennial brown bracket is Fomitiporia robusta (or are directed to do so by the software suggestions), so decided to make a general post to clarify the issue.

There are two main problems with using Fomitiporia robusta for Australian species:
(1) there are MANY species (and many genera) of perennial brown brackets (Hymenochaetaceae) in Australia, not just one;
(2) The type locality of Fomitiporia robusta is Finland, and there are no confirmed (DNA-confirmed) collections of Fomitiporia robusta from Australia - so it is very likely that the name does not even apply. There are however several native species of Fomitiporia, and records of F. robusta are probably misidentifications of those.

So at least the majority of past Australian records of ‘Fomitiporia robusta’ are not this species, and some are not even Fomitiporia. The reason for misunderstanding is probably that, in most Australian field guides, the only perennial Hymenochaetaceae species covered is called "Phellinus robustus" (=Fomitiporia robusta). However single species does injustice to the wide diversity of medium to large perennial Hymenochaetaceae in Australia, which includes at least 40 species of Inocutis, Fomitiporia, Fomitiporella, Fulvifomes, Phellinus, Pseudoinonotus, Pseudophylloporia, Sanghuangporus, and Tropicoporus.

So merely knowing that you have a perennial brown bracket is insufficient even to place it to genus, and the best identification is simply "Hymenochaetaceae".

to go further than family, you need to know additional information. Host plant, spore colour (white, yellow or brown), pores per mm, cap cracking, and flesh consistency are necessary characters to identify perennial Hymenochaetaceae to either genus or species. For full species identification microscopic characters (spore dimensions, spore wall thickness, and setae) are often necessary.

For perennial, pileate, medium to large species:
Spores white = Fomitiporia, Phellinus, Pseudoinonotus, also compare Fuscoporia and Pyrroderma
Spores yellow = Fulvifomes, Inocutis (plus a few odd species of other genera)
Spores brown = Fomitiporella, Fulvifomes, Pseudophylloporia, Sanghuangporus, and Tropicoporus

Beyond that, key characters to distinguish species are: plant host (especially whether Eucalyptus, Melaleuca, Acacia or other), whether host is living or dead, pore dimensions, cap surface cracking, internal flesh colour, whether there is a granular or marbled core at the base in section, whether the flesh is homogenous or divided into two layers separated by a thin dark line, and whether tropical or temperate distribution. Tropical and subtropical areas have the greatest diversity.

Fortunately most genera have only a few pileate species, so knowing the above characters gets you a long way to identifying to species. Unfortunately, many species remain undescribed, and new species or new Australian records are discovered regularly, so we are a way off having a comprehensive key to them all.

For now, please just use Hymenochaetaceae if you are unsure, and when collecting, do your best to locate spore deposit under the bracket. You can often see spore colour by spore caught in spider web just below the fruitbody close to the trunk. If you can see spores, please record it, along with the host tree identify, when making your iNaturalist record.