Salix matsudana Tortuosa has been photographed at Jerrabomberra and I was told the ones in Mugga Mugga were probably S. matsudana Tortuosa. I don't know how to tell the hybrids. I don't know if I have photos showing catkins but I will add photos when I can.
This is the same plant as http://canberranaturemap.org/Community/Sightings/Details/1946914 which Michael Mulvaney IDed as Salix nigra X matsudana from quite a poor photo. It has shown quite a lot of development over the last 5 months
Yes it is difficult to tell apart. I decided on the hydrid Salix nigra X matsundra because the leaves seem to be flat or only have one curve, while in matsudana many o the leaves appear to be doubly curved, like a sack slide at the Canberra show. Ithink the only thing I can say for certain is S. matsudana is at least one of the parents