Both host species [Cardamine spp.] and rust are endemic to New Zealand. The host plants occur in subalpine regions of both islands; the rust occurs only in the South Island.

Specimens examined. Puccinia cruciferarum Rud. subsp. inornata (G.H. Cunn.) Walker, on Cardamine bilobata Kirk, Castle Hill, Canterbury, N.Z., Jan. 1928, G.H. Cunningham, PDD 3104 (microscope slides as DAR 41556); on Cardamine debilis Banks ex DC., Macrae's, Otago, N.Z., Nov. 1921, W.D. Reid, PDD 444 (see note), holotype, (microscope slides as DAR 41553); Govenor's Bay, Canterbury, N.Z., Sept. 1923, J.F. Tapley, PDD 10056 (microscope slides as DAR 41557); on Cardamine sp., near Blue Lake, Kosciusko National Park, N.S.W., March 1980, A. Gibbs, DAR 35287 (first record in Australia); Club Lake, Kosciusko National Park, Feb. 1981, A. Gibbs, DAR 37839; Kosciusko National Park, April 1981, A. Gibbs, DAR 41558.
Note. In the above list, the PDD number of the holotype of P. cruciferarum subsp. inornata is given as '444'. This is the number typed on the outside label. The number written in ink on the inside label is '440'. The word 'TYPE' is also written on the inside label and the details given agree exactly with those listed for the TYPE collection by Cunningham (1923).

Telia on leaf blades and petioles which are often twisted and slightly swollen, heavily infected leaves much distorted; telia reddish brown, to 1 mm diam., occurring singly or more often in clusters up to 2-3 mm diam. on leaf blades or elongated along petioles for 6-7 mm. Teliospores (Figs 5 and 6) golden brown to reddish brown, 24-37 x 10-14 µm, constricted at the septum which may sometimes be slightly above the middle, making the basal cell a little longer than the apical cell, cells of equal width or apical cell sometimes slightly wider; wall 2-2.5 µm thick, finely roughened with very small 0.4-0.7 µm diam. warts, 0.5 µm high and 1.5(-2) µm apart, uniformly scattered over the whole surface of the spore; germ pore apical in the upper cell, basal and next to the pedicel in the lower cell, both pores covered by a hyaline papilla up to 2(-2.5) µm high and 4-5 µm wide; pedicel short, usually less than 10 µm long, sometimes absent, 4-5 µm wide at the hilum. There is a tendency in a small proportion of spores for the two cells to separate cleanly at the central septum.

Puccinia cruciferarum is a microcyclic rust lacking pycnia which occurs on several species of Cardamine in arctic and alpine areas of Europe and North America (especially Canada and Alaska). It has been studied in detail by Savile (1964), who recognized in the northern hemisphere collections examined four geographic populations distinguished by the size and distribution of the warts on the spore wall, the size of the papilla covering the germ pore in the upper cell of the teliospores and the position of the germ pore in the lower cell. He placed these populations in four subspecies (see Table 12).
The finding in March 1980 of a rust on Cardamine sp. in the Kosciusko alpine area of New South Wales represented a new record for Australia of a rust on a member of the family Brassicaceae and prompted a more detailed investigation of its identity. Comparison with the description and later with the type and other collections of Puccinia inornata described by Cunningham (1923, 1931) on two species of Cardamine in New Zealand, showed that the Australian rust was identical and initially collections were disposed in DAR as P. inornata. However, a study of Savile's (1964) paper and some northern hemisphere collections of P. cruciferarum has led to the conclusion that P. inornata would be better considered as a subspecies (geographic population) of P. cruciferarum, differing from those described by Savile in the combination of smaller spores, small warts covering the whole outer surface of the teliospores and a completely depressed germ pore, located at the base of the lower cell near the pedicel. None of the northern hemisphere subspecies shows this combination of characters and, in particular, complete depression of the germ pore in the lower cell.
From both the taxonomic and geographic distribution viewpoints, the position of Puccinia cardamines-cordatae Diet. & Neger described on Cardamine cordata Barn. and C. reniformis Ph. from the Andes in Chile (Sydow and Sydow 1904; Mujica et al. 1980) is of considerable interest. No specimens of this rust have been seen during the current investigation and, from the available descriptions, no firm conclusions about its possible place in the P. cruciferarum complex can be drawn. In reported spore size (27-37 x 10-15 µm) it is much closer to P. cruciferarum subsp. inornata than to any of the northern hemisphere subspecies.