An interesting character of many "Cyanea" is their tendency to grow spines or thorns on the stem and leaves (see the photo of "Cyanea platyphylla"). This is most pronounced in younger plants, and some species undergo a kind of metamorphosis as they mature, to the extent that different growth stages were described as separate species, due in part to the presence or absence of spines. The purpose of the spines was puzzling, since in most island situations there is a tendency for plants to lose defenses - Hawaii is noted for its nettle-less nettles, mintless mints, and (not quite) thornless raspberries - and no native browsing animals were known. However, it is now believed that the spines were a defense against the moa-nalo, giant browsing geese and goose-like ducks that formerly inhabited the islands (Givnish et al. 1995). These birds were apparently driven extinct by the Hawaiians before Europeans reached the islands, but their evolutionary effects live on.