Because the islands of Hawaii is located about 2,300 miles away from any continents, they are the most isolated place on the planet. That means plant and animal life arrived very infrequently and then evolved in isolation from the rest of the world. For this reason, many of Hawaii's plants have evolved to be endemic (native to Hawaii).
Arriving sporadically as seeds or spores attached to migrating birds or insects caught in high winds, these early plants flourished with little to no opposition in Hawaii, and evolved to reflect this. With no grazing animals on the islands, plants in Hawaii needed no defense mechanisms. That's why Hawaiian holly is spineless, and Hawaiian nettles don't sting. Hawaiian mint is tasteless, where normally a strong taste fends off potential grazers.
Once Polynesians and later Europeans arrived on the islands, they cleared forests and introduced non-indigenous plants and animals, leading to the extinction of many endemic plants.