Other families are poorly represented, the palm family 

 (Palmae) only by Prichardia, the laurel family 

 (Lauraceae) by 2 species, and the flacourtia family 

 (Flacourtiaceae) by 1. 



However, a few tropical tree species are widespread. 

 For example, 2 species of Puerto Rico and the Virgin 

 Islands are represented also on the American continent 

 north to southern Florida (a variety of 1 also to southern 

 Arizona) and reappear again in Hawaii: Sapindus 

 saponaria L., wingleaf soapberry, and Dodonaea viscosa 

 (L.) Jacq., hopbush. 



Several significant conclusions can be made from the 

 comparison in table 1. The unique tree flora of the 

 Hawaiian Islands is definitely poor or impoverished (and 

 Puerto Rico slightly so). Hawaii has fewer than one-half 

 as many plant families with trees as does Puerto Rico (40 

 in contrast to 85) and slightly more than one-fourth as 

 many genera with trees (70 in contrast to 273). 



The number of tree species in all Hawaiian Islands 

 combined is somewhat lower than that in Puerto Rico 

 and the Virgin Islands, about two-thirds if the named 

 segregates are accepted (370 in contrast to 551) or slightly 

 more than one-half if the number of species is conserv- 

 atively treated as fewer than 300. 



The small number of tree species is more obvious when 

 totals by islands are compared. The total on each of the 4 

 larger Hawaiian Islands (119-165) is only about one- 

 fourth to one-third as many as in Puerto Rico (539). (The 

 relatively small Virgin Islands have low numbers not 

 available individually.) 



More striking contrasts are shown by comparison with 

 local lists within Puerto Rico. The Caribbean National 

 Forest in the Luquillo Mountains possesses 225 native 

 tree species, as noted, more than any one of the Hawaiian 

 Islands. Oahu, which has been thoroughly explored by 

 botanists working from Honolulu during more than a 

 century, has only about 165 tree species (including weak 

 segregates). Kauai, the oldest island of the group, has 

 134, and Hawaii, the largest, only 119. 



The percentage of endemism in Hawaii is the highest in 

 the world. Nearly all the tree species are native only 

 within that archipelago (96-97%), while one-fourth the 

 trees of Puerto Rico and the Virgin Islands are endemic 

 (25.8%). Of course, the total number of endemic tree 

 species is greater in all the Hawaiian Islands combined 

 (289-359) than in Puerto Rico and the Virgin Islands 

 together (142), more than twice as many. 



Even so, the more numerous endemic species of the 

 Hawaiian Islands show somewhat less diversity among 

 fewer genera (66 in contrast to 94) and fewer families (40 

 in contrast to 50). Obviously, in Hawaii each genus with 

 endemic species has more species, about 5, in contrast to 

 1.5 in Puerto Rico. However, the number is increased by 

 a few large genera with many poorly defined species. 

 Several of the closely related Hawaiian species (also 



named varieties) have become extinct (21 in contrast to 

 0?). Thus, Puerto Rico and the Virgin Islands have a 

 somewhat richer or greater display of mostly unrelated, 

 widely differing endemics. 



On an island to island basis, Puerto Rico has almost as 

 many endemic tree species as any one of the Hawaiian 

 Islands. Puerto Rico (with 539 species of native trees) has 

 136 of the 142 species endemic to Puerto Rico and the 

 Virgin Islands combined, or 106 not found on any 

 smaller island. 



Hawaii has a large number of endemic tree genera, 17 

 (in 12 plant families), as compiled by Stone (22). Puerto 

 Rico has only 1, as noted above, apparently because 

 several other old local genera have spread into other isles. 



Endemic species may be "new," such as in large 

 groups of closely related species of continuous ranges, or 

 "old," of few species with separated ranges. Hawaii has 

 several very large genera with many "new" endemics as 

 well as others with few "old" endemics. The endemic tree 

 species of Puerto Rico and the Virgin Islands, mostly 1 or 

 2 hi a genus, are "old," largely isolated, and not closely 

 related. 



Geographic distribution of the endemic tree species 

 varies somewhat in the two island groups. For detailed 

 comparison, species maps would be desirable. Appar- 

 ently, the endemic tree species of Hawaii are somewhat 

 scattered among different mountain peaks and ranges of 

 several islands. In Puerto Rico, the endemic tree species 

 are mostly concentrated within a few mountain areas of 

 one island, especially the Luquillo Mountains and Cen- 

 tral Cordillera. Most of Puerto Rico's endemic tree 

 species grow wild within six public forests. In Hawaii, 

 protection of the greater number of endemics would re- 

 quire a larger number of preserves. 



The palm family, Palmae, offers a very interesting 

 comparison. The relatively young Hawaiian Islands have 

 a single genus of native palms. Pritchardia has 33 named 

 species, "young" and weak, scattered through several 

 islands (a few other species elsewhere), though the 

 number probably should be reduced to less than half. 

 Puerto Rico, a very old island, has 10 species of native 

 palms, each in a different genus, as already noted. Seven 

 are endemic "old" species without relatives on the island. 

 Thus, Puerto Rico has the greater display of endemic 

 palms. 



Only a few native tree species in all these islands appear 

 to need additional protection. Many are rare, but most 

 are within public forests. As classed here, rare endemic 

 species needing protection (some could be proposed as 

 endangered) total about 50 species in Hawaii and 17 in 

 Puerto Rico and the Virgin Islands. Rare endemic species 

 to be watched (some could be proposed as threatened) 

 total about 20 species in Hawaii and 22 in these West In- 

 dian islands. 



21 



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