This lichen has a moderately attached, thin and flexible
thallus that can grow up to wide. The are unevenly shaped and connected in the centre, but separate near the tips, measuring 2–4 mm wide. The edges of the lobes are smooth and occasionally wavy, appearing flat, without any . The top surface is a dusty grey-green colour, unevenly cracked in the centre with visible
isidia, which are inflated and mostly branched, forming clusters that can be up to 0.5 mm wide and up to 0.8–1 mm high. The
medulla is white, while the bottom surface is black and dull, with a narrow brown margin measuring up to 1 mm wide. The
rhizines are black, not densely spread, and have a coarse and simple appearance. No
apothecia or were observed.
Canoparmelia rarotongensis produces
atranorin,
chloroatranorin in the and
lecanoric acid in the medulla as major
lichen products, and trace amounts of
orsellinic acid, and
orcinol. Before this species, lecanoric acid had not been reported to occur in the genus
Canoparmelia. The expected results of standard chemical
spot tests are K+ (yellow) in the cortex, and K−, C+ (red), PD− in the medulla. ==References==