The most conspicuous feature of Hawaii, for someone who has never been there before, is undeniably the lava. The entire terrestrial surface of the islands is made of this stuff, a dark, craggy, ominous-looking substrate which looks suspiciously like it should still be hot to the touch from its eruptive moment of creation. In fact, for much of the lava on the south-east side of the Big Island, in the active volcanic zone, this is almost literally true. Many of these flows were formed within the last century, some of them in the last 30-40 years, and lava is still actively erupting today.
The next thing a newcomer to Hawaii might notice, after oggling the lava, is the green stuff on the lava. That would be the plants. And in most cases, the first colonists and only plants intrepid to live out on this stuff, are ferns. Ferns are excellent dispersers because of their lightweight, durable spores, so they are often the first plants to reach newly-available substrates, like lava. Here's a small sampling to give you a feel for the desolation of the lava, and hopefully, an appreciation for the indomitable nature of the ferns that live on it!
The ferns in the right photo above and at the top of this post are species of Sadleria, and the small ferns in the next photo down are Polypodium pellucidum.