Relationships of the Endemic Species 



The rare and local tree species of Puerto Rico and the 

 Virgin Islands can serve as a background for studies of 

 the origin and relationships of the plant life. Endemic 

 species, having developed in isolation from relatives 

 elsewhere, are particularly significant in such studies. 

 Some general, preliminary observations on the endemic 

 species and endemic genera may be mentioned here. 



An analysis of the geographic distribution of the native 

 tree species of these islands was presented in the second 

 volume (15, p. 15). According to their patterns of 

 geographic, distribution, the species may be arranged in 

 three main groups: (1) More than two-fifths (229 species, 

 41.9%) also on the continent, mainly South America but 

 also Central America (or Mexico or Florida); (2) one- 

 third (177 species, 32.4%) in West Indies but not on the 

 continent; and (3) one-fourth (141 species, 25.7%) 

 endemic to Puerto Rico and the Virgin Islands. The main 

 source of the original immigrants or ancestral species was 

 South America, though Central America was another. 



The endemic species in that compilation of 547 native 

 tree species were grouped further as follows: 

 Endemic to Puerto Rico and/or Virgin Islands, 141 

 species, 25.7%. 



Puerto Rico and Virgin Islands only, 21 species, 



3.8%. 



Puerto Rico and adjacent island only, 6 species, 



1.1%. 



Puerto Rico only, 109 species, 19.9%. 



Virgin Islands only, 5 species, 0.9%. 



The study of the relationships of the trees of the Lu- 

 quillo Mountains shows what could be done on a larger 

 scale (7). Some similarities among endemics and 

 nonendemics were indicated. For example, 2 or more 

 related endemic species apparently were derived from the 

 same ancestor or original immigrant. Paired species were 

 observed on mountains, which are climatic islands within 

 the larger island. Thus, Magnolia splendens is endemic to 

 Luquillo Mountains, and M. portoricensis to the central 

 and western mountains. 



The endemic trees of Puerto Rico and the Virgin 

 Islands, as listed here, total 142 species. These are 

 grouped into 94 genera and 50 plant families. In com- 

 parison, all native trees total 551 species in 273 genera 

 and 85 plant families. 



Endemic tree species are more common in some genera 

 than others. Possibly some groups evoWe more rapidly 

 than others. More endemics may be expected in large 

 genera also. 



Genera with the greatest numbers of endemic tree 

 species are as follows: Eugenia 10; Calyptranthes and 

 Miconia 5; Ternstroemia 4; and Antirhea, Brunfelsia, 

 Coccoloba, Ilex, Maytenus, Tabebuia, and Tetrazygia 3 

 each. Fifteen other genera have 2 endemic tree species, 

 while 68 have only 1. Several genera also contain related 



endemics that are shrubs. In comparison, the largest 

 genera in number of native tree species are Eugenia 23, 

 Miconia 17, and Coccoloba 12. 



Plant families with the most endemic tree species are: 

 Myrtaceae, 19 species in 5 genera; Melastomataceae, 12 

 species in 6 genera; Palmae, 7 species in 7 genera; 

 Sapotaceae, 5 species in 5 genera; Solanaceae, 5 species in 

 3 genera; and Theaceae, 5 species in 2 genera. 



The palm family, Palmae, apparently is of great age in 

 Puerto Rico. The 10 native genera are represented by a 

 single species each, and 7 have changed after arrival into 

 species not found elsewhere. 



Species New to Science 



Very few tree species new to science have been found in 

 recent years in Puerto Rico and none in the Virgin 

 Islands, as noted in the second volume (15, p. 17). After 

 completion of the flora by Britton and Wilson (2), only 

 the following 8 tree species have been published by later 

 authors as new: 



Linociera holdridgii Camp & Monachino (Lloydia 2: 



223. 1939) 



Myrica holdridgeana Lundell (Contrib. Univ. Mich. 



Herbarium 7: 5. 1942.) 



Licaria brittoniana Allen & Gregory (Brittonia 7: 



267. 1951) 



Byrsonima wadsworthii Little (Phytologia 4: 417, 



fig. 1953) 



Calptranthes luquillensis Alain (Bull. Torrey Bot. 



Club 90: 189. 1963) 



Eugenia haematocarpa Alain (Bull. Torrey Bot. 



Club 90: 190. 1963) 



Phialanthus grandifolius Alain (Bull. Torrey Bot. 



Club 92: 302. 1965) 



Alsophila bryophila Tryon (Rhodora 74: 443, figs. 



9-10. 1972)" 

 All 8 are endemic to Puerto Rico. None needs special 

 protection. These 2 are in list 3, Endemic Species To Be 

 Watched: Calyptranthes luquillensis, Eugenia 

 haematocarpa. These 3 are in list 4, Other Rare Endemic 

 Species: Linociera holdridgii, Myrica holdridgeana, 

 Phialanthus grandifolius. The other 3 are in list 5, Com- 

 mon Endemic Species: Licaria brittoniana, Byrsonima 

 wadsworthii, Alsophila bryophila. Several other new 

 species described as shrubs may be observed later to at- 

 tain tree size. 



Endemic Genera 



Several endemic tree species of Puerto Rico are so dif- 

 ferent from others of their plant families that they have 

 been placed in new genera. These species have changed 

 sufficiently from their original immigrant or ancestral 

 species to merit a new generic as well as specific name. 



15 



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