'Aku 'Aku are a striking endangered plant found in widely distributed wet forests on Hawai'i. Young plants look very similar to 'aku (c. tritomantha), but the two species aren't closely related. The most obvious way to differentiate them is by their flowering behavior. 'Aku produce larger flowers among the crown leaves of the adult plant, whereas 'aku 'aku can flower precociously, with smaller flowers on stalks lower along the main stem among the leaves. They often look very sickly, with a few small tattered or rotting leaves. Sometimes all of the leaves will fall off and the plant will appear nearly dead, but new leaves will start budding out a couple weeks later.

The species seems a bit polymorphic, but that might be an illusion. The Laupahoehoe greenhouse plants look a bit different from the Upper Waiakea Forest Reserve colonies, but some of that may be the effect of greenhouse living. Some of the variation may be due to the beating many of the plants take from falling tree fern fronds, or perhaps due to different levels of sunlight. Is hybridization with other cyanea possible?