I believe the key uses the presence or absence of hooked spines on the burrs to seperate these two although of course that’s only so useful. When plants are exclusively in leaf I find the most accurate detail in the presence of hairs on the leaf undersurface, in A.ovina they are densely pilose whilst in A.echinata they are restricted to the midrib and leaf edge.
Generally speaking A.echinata is somewhat smaller than A.ovina which also has a more erect form. I don’t find any profound differences between habitat preference; both occur in grassland, box gum woodland etc.
Another good tip is that A.echinata is clonal, so will often form little groups of small rosettes, whilst A.ovina is not - though that’s Dr Meredith Cosgrove’s input not mine!!
