DISTRIBUTION OF THE MOKE PROMINENT NATUEAL ORDERS. 241 



Mexican. Hydrangea, of which one Andine species inhabits Mexico, is common to 

 America and Eastern Asia. 



Crassulacece. 



Conspicuous among Mexican succulent plants are the numerous forms of the section 

 Ucheveria of Cotyledon, of which there are two or three outliers in California and 

 Texas. There is also a considerable number and variety of forms of Sedum, a genus of 

 the northern hemisphere extending to the Andes. Some, like S. dendroideum, are of 

 shrubby habit; S. cupressoides has small closely imbricated leaves like a cypress or 

 lycopod ; and several are small annual plants. 



Hamamelidece. 



An order which is chiefly Asiatic, and rarer in Africa, and only found in Eastern 

 North America, having its southern limit in Central America, where there are one or 

 two species of Liquidambar. This genus inhabits eastern North America, Asia Minor, 

 and Eastern Asia. Liquidambar trees are sufficiently abundant in some of the moun- 

 tain forests of Mexico and Central America to form an appreciable element. 



Myrtacece. 



This order, which is wholly shrubby and arboreous, and eleventh as to number of 

 species among the orders of phanerogams, is widely spread in temperate and tropical 

 regions, though very rare in the north temperate zone. We have only one from North 

 Mexico, and that from San Luis Potosi ; about half a dozen inhabit South Florida, one 

 the Bermudas, one Europe, and none temperate China and Japan. On the other hand, 

 they abound in Australasia and temperate South America, while only about fifteen 

 species have been found in South Africa, the most interesting being Metrosideros 

 angustifolia ; the genus being otherwise Australasian and Polynesian. The Chilian 

 monotypic Tepualia is closely allied to Metrosideros, and the only Leptosperm in 

 America. We have fifty-eight species of Myrtacese (fifty-one endemic) belonging to 

 twelve genera. All the species are restricted to America. 



The Australasian Myrtaceae belong mainly to two tribes almost entirely restricted to 

 the region, and they number about 700 species, belonging to forty genera. In Australia 

 itself there are 660 species, and they constitute the next to the largest order; Legu- 

 minosse alone exceeding them. Berg* estimates the total American Myrtaceae at 

 1726 species, 696 of them being concentrated in Brazil; but it should be remembered 

 that he took a very narrow view of species. Sixteen-seventeenths of them belong to 

 the Myrtese, or true myrtles. He very elaborately tabulates the distribution of the 

 whole of the American Myrtacese in the work cited. The almost exclusively tropical 



* Flora Brasiliensis, xiv. 1, p. 619. 



