INTRODUCTORY CHAPTER. xliii 



Euphorbiacese, with about one-twentieth of the species of the flora, is not so 

 well represented generically as the order just mentioned; ten of the species — 

 seven being endemic — belong to Euphorbia itself. Four-sevenths of the whole 

 species are endemic. The most noteworthy feature in this family on Socotra, 

 is the occurrence of the fleshy leafless tree-euphorbia, E. arbuscula, which to 

 some extent may be said to mimic the dragon's-blood tree, D. Cinnabari. It 

 has a near ally in E. aphytta of the Canary Islands, along with which occurs, 

 it is interesting to observe, the dragon's-blood tree of these islands, D. Draco. 

 Euphorbia spiralis is another fleshy, leafless, and spiny form, with south 

 African and Atlantic Island representatives. The presence of Hildebrandt's 

 Somali-land box-tree, Buxus Hildebrandti, must not be passed over, nor the 

 fact that there are four endemic species of Croton, and an endemic re- 

 presentative of Cephalocroton, a genus hitherto known in two species — one from 

 Mozambique and one from Nile-land. 



Acanthaceae is, in some ways, the order with the most remarkable de- 

 velopment in Socotra. It comprises twenty-seven species, i.e., it forms nearly 

 one-twenty-first part of the flora, and of these species all but six, or seven-ninths 

 of the whole order, are endemic. Thus one-tenth of the endemic plants is 

 acanthaceous. The twenty-seven species are included in fifteen genera, and of 

 these three are endemic, and seven more are represented only by endemic 

 species — one of them being tritypic and the other ditypic — so that over one- 

 seventh of the endemic genera is acanthaceous. In this family are some of the 

 prettiest flowering shrubs, such, for instance, as Ruellia insignis, Ruellia carnea, 

 Barleria aculeata, and the species of Ballochia. The endemic genera Ballochia, 

 Trichocalyx, Ancalanthus, have allies in genera of the adjacent continents. But 

 in addition to this element of endemic genera, it is noteworthy that several of the 

 endemic species referred to other genera show divergence from the characters 

 ascribed to these. Thus Blepharis spiculifolia has several floral characters 

 modifying those described, for Blepharis, and similarly the generic character of 

 Barleria is affected by Barleria tetracantha and Barleria argentea, which have 

 only one ovule in each cell of the ovary, quite an exceptional character in the 

 order. Neur acanthus aculeatus and N. capitatus also differ in habit from the 

 rest of the genus, and the hygroscopic inflorescences of the latter are peculiar. 

 Justicia heterocai'pa is noteworthy on account of its diversely formed fruits 

 and seeds. Anisotes diversifolius is an endemic representative of a genus 

 known only by a single species in Arabia, and, since the description of the 

 plant was written, by another from east tropical iVfrica, collected by Mr H. H. 

 Johnston. Ecbolium striatum is also an endemic species of a genus elsewhere 

 represented by one variable aud widely-spread species. 



There is not much noteworthy in Cyperacese as it forms part of the 

 Socotran flora. Thirteen of the species belong to Cyperus, and Fimbristylis 



