FLOBTJLA ADENEKSTS. 



JX 



Scrophularineae . . . 



Acanthacese 



VerbenacejE 



Labiatse 



Plumbagineae 



Salvadoraceae 



Phytolaccaceae . . . 



Salsolacese 



Amarantacese 



Genera. Species, 

 . 4 4 



Paronychiaceae 



Nyctaginese 



Euphorbiacea; 



Urticacea? 



Gnetaceae 



Amaryllideae 



Cyperaceae 



Gramineae 9 



a. Species. 

 1 



Total number of natural orders, 41 ; of genera, 79 ; of species, 94. 



This aggregation, within so considerable an area, of almost soli- 

 tary representatives of genera, is probably a feature peculiar to 

 isolated desert localities. It first attracted my attention during 

 my visit to Aden in 1859, and I have since drawn up tables of the 

 species, genera, and natural orders of the Floras of Hong-Kong, 

 Ischia, and Gibraltar ; the results of which confirm my first im- 

 pression. Hong-Kong and Ischia are nearly equal to Aden in 

 area, and, though differing from it in being detached from the 

 mainland, the sea has proved a less insurmountable barrier to the 

 introduction of species from the neighbouring countries than the 

 unpropitious climate of Aden, and the inaccessible walls of rock 

 by which it is cut off from the rest of Arabia. Gibraltar, though 

 of smaller extent than Aden, yet possesses so many features in 

 common with it, as fully to justify a comparison of their floras. 

 I am indebted to Mr. Bentham for the materials from which the 

 Table of the Hong-Kong species is deduced. That of the flora of 

 Ischia is taken from Gussone's elaborate Florula of that island*, 

 all the cultivated and doubtful species and genera having been 

 carefully rejected. Kelaart's ' Flora Calpensis ' is the authority 

 for the list of species of Gibraltar. 



Table showing the proportion of Natural Orders, Genera, and Species 

 in the Floras of Aden, Hong-Kong, Ischia, and Gibraltar. 



Aden 



Hong-Kong 

 Ischia 



Natural Orders. 



1 



1 

 1 



Genera. 

 1-92 

 459 

 432 

 350 



Species 

 229 

 7-90 

 923 



Gibraltar . . . 



1 



6-70 



The actual paucity of species in the vegetation of Aden, though 

 indicated by this Table, will be more distinctly seen by a reference 

 to the numbers from which the proportions were obtained. 

 * ' Enumeratio Planfcarum Vascularum Inarimensium.' 



