234 BOTANY OF SOCOTRA. 



A monotypic genus undoubtedly referable to the tribe Verbenece, and 

 decidedly Lantanoid in habit, But, from the genus Lanlana and its allies the 

 4-cellcd ovary and the fruit separate it, and its closest affinity appears to be 

 with the tropical and subtropical American genus Cithareocylum, the species of 

 which, twenty in number, are spread from Brazil and Bolivia to Mexico. 



The technical characters by which it is separated from its American ally are 

 found in the andrcecium. In Citharexylum the connective is enlarged behind 

 the anther, forming a sort of cushion upon which the parallel lobes lie, and this 

 cushion often forms a small apical antherine appendage. In the Socotran plant 

 the anthers are minute, divergent at the base, without an enlarged connective. 

 In other characters the genera agree well, — in inflorescence, calyx, corolla, 

 ovary, and most remarkably in the fruit, which is somewhat peculiar, having in 

 the centre between the two-celled pyrenes a cavity larger than the loculi. 

 This has given the name to our genus. In habit there is a slight difference. 

 Species of Citharexylum are commonly shining, somewhat glabrous, plants, 

 frequently spiny. Ours is an unarmed pubescent shrub. But there are species 

 of Citharexylum which are tomentose. 



Altogether the affinity of the Socotran and the American plant is very close, 

 so close indeed that, apart from their distribution, one would probably have 

 been inclined to regard the Socotran plant as a Citharexylum, But the anti- 

 podean distribution makes the union at present less advisable, when there are 

 such differences in the staminal whorl. 



Whether congeneric or not the affinity is clear, and is interesting from the 

 point of view of geographical distribution, as it adds another to those instances 

 of species endemic in the Indian Ocean islands which find their nearest allies in 

 new world or almost antipodean forms of either the same or closely related 

 genera. Perhaps a more special interest attaches to this Socotran plant inas- 

 much as in another genus, Nesogenes, of this order, we witness such features of 

 distribution ; the endemic Rodriguez species N. decumbens, Balf. fil. (in Trans. 

 Roy. Soc. 108 extra vol. 362), having its only congener N. euphrasioides, Alph. 

 DC. (Prod. xi. 703), a native of the Polynesian islands. I have elsewhere 

 alluded to these antipodean affinities, but may here mention as other examples 

 our Socotran Geraniaceous monotypic Dirachma, with its American allies 

 Wendtia and Viviania ; the monotypic Turneraceous Mathurina of Rodriguez, 

 whose nearest ally is the monotypic Erblichia of Central America ; the American 

 Thamnosma (Rutacerc), with one Socotran and two north American species ; 

 the small Sapotaceous genus Labourdonnaisia, with four peculiar Mascarene 

 species, one endemic in Natal and a sixth in Cuba ; and the large Laurineous 

 Ocotea, a genus exclusively tropical and subtropical American, but for three old 

 world species, one of them occurring in the Canary Islands, one in south 

 Africa, and one in Madagascar. 



