While the rainforests of Kauai are often called jungles, I don’t know if they qualify in a scientific sense because they tend to lack biodiversity. Being as isolated as the island is, there are relatively few species here, both plants and especially animals. However, to the lay person, there are plenty of unknown and unusual plants to make the rainforests here appear exotic. One of my favorites is the tree fern that can be found in up in the wet forests and is sometimes used in landscaping lower down.
Called “hapu’u” (PDF link) in Hawaiian, the most common native tree fern is Cibotium glaucum. It seems like there is also a species endemic to Kaua’i (found nowhere else naturally) called Cibotium nealiae. Sadly, Australian tree ferns grow better in the drier climate around the coast, so they have been imported for landscaping.
Here is a picture of one, probably Cibotium glaucum, seen from near the top of the Powerline Trail. The other trails where I know you can see tree ferns are the Alakai Swamp Boardwalk and the Mohihi-Waialae trail.
