Key based on data from the original description of subspecies dunensis. It needs to be tested.
1Robust plant, mostly 20-50 cm high; petals light yellow; valves 4-6 mm in diam., its discs (sub)glabrous or scabridulous, without distinctly thickened margins
1'Slender plant, 5-15 mm high; petals dark yellow; valves 2.5-3.5 mm in diam., its discs shortly hairy, margins and center with somewhat longer hairs, with slightly thickened margins