Interesting topic, and as Loxley Clovis said, hawaii is indeed a very diverse place, but there are a few things that are wrong
1. Brazil is indeed the biggest country in south america, but is far from being the most diverse in life zones "it lacks both high mountains and deserts". Venezuela, colombia, peru, ecuador, bolivia and Argentina all have lifezones ranging from deserts and tropical rain forest in one extreme to glaciers on the other as the andes are the highest mountains in the world after the himalayas. I don't include chile on the list as it lacks tropical rain forest. Argentina alone may have even more life zones "Not sure about it" than the whole US "including alaska and hawaii"
2. Hawaii is very diverse but it lacks a few thing such as tropical life zones, even thought its in the tropics, the average annual temperature is not hot enough to classify as any tropical life zones according to the holdridge system, and of the 7 altitude level "basal, premontane, lower montane, montane, subalpine, alpine, and nival" it lacks the last two. So perhaps its indeed the most diverse island in the world but its not the most diverse location in the world. For example in my country, Colombia, municipios are the equivalent to counties. The municipio where I live, Santa Marta, has an area of 2,393 km2 "923 square miles" and its territory goes from the carribean sea to 5.800 mts "19.030 feet" in the sierra nevada de Santa Marta "the highest coastal mountain in the world" it has almost everything hawaii has plus alpine tundra and glaciers
