1963] 



BOTANY OF THE GUAYANA HIGHLANDS PART V 



9 



Table 1. Altitudinal and Geographical Distribution of Guayana Xy 

 Section Nematopus, 69 Species; Section Xyris, 3 Species. 



ris. 



HIGH ALTITUDE ENDEMICS 



X. erythema M. & S. 



X. thysanolepis M. & S. 



X. concinna N. E. Br. 



X. submontana Gl. 



X. sipapoa M. & S. 



X. stenophylloides Malme 



X. atriceps Malme 



X. decussata Gl. 



X. witsenioides Oliver 



X. riparia M. & S. 



X. ptariana Steyerni. 



X. xiphophylla M. & S. 



X. bicephala Gl. 



X. roraimae Malme 



X. albescens Steyerm. 



X. setigera Oliver 



X. culmenicola Steyerm. 



X. tatei Malme 



X. lugubris Malme 



X. scabridula Steyerm. 



X. delicatula M. & S. 



X. juncifolia M. & S. 



X. neblinae M. & S. 



X. lanulobractea Steyerm. 



X. cyperoides Gl. 



X. rugulosa M. & 8. 



X. bicostata M. & S. 



X. steyermarMi M. & S. 



X. connosepala Lanj. 



X. duidensis Malme 



X. contracta M. & S. 



X. frondosa M. & S. 



X. pratensis M. & S. 



X. yutajensis M. & S. 



LOW ALTITUDE ENDEMICS 



X. involucrata Nees 



X. spruceana Malme 



X. cryptantha M. & S. 



X. uleana Malme 



X. esmeraldae Steyerm. 



X. exserta I. & S. 



X. fusiformis M. & S. 



X. oxylepis I. & S. 



X. garcia-barrigae I. & S. 



X. wurdackii M. & S. 



X. aquatica I. & S. 



X. terrestris I. & S. 



X. stenostachya Steyerm. 



X. arachnoidea M. & S. 



X. globosa Alb. Xilss. 



X. yapobodensis I. & S. 



X. filiscapa Malme 



X. siibuniflora Malme 



X. rubrolimbata Hiemerl 



X. applanata I. & S. 



X. frequens M. & S. 



X. teinosperma I. & S. 



X. araracuarae M. & S. 



X. carinata M. & S. 



X. cuatrecasana I. & S. 



X. subglabrata Malme 



GUAYANA-BRASILIA 



X. seubertii Alb. Nilss. 

 X. hymenachne Mart. 

 X. lomatophylla Mart. 

 X. guianensis Steud. 

 X. lacerata Pohl ex Seub. 

 X. paraensis Poepp. 



WIDESPREAD OR OTHER 



X. caroliniana Walt. 

 X. fallax Malme 

 X. longiceps Malme 

 X. surinamensis Spreng. 

 X. malmeana L. B. Smith 

 X. savanensis Miq. 



Brazilian Highland distribution. Of these, X. lomatophylla is rather broadly 

 distributed in lowland Guayana, but is more sparingly found southward. 



And finally six species (four of the sect. Nematopus, and two of the sect. 

 Xyris) have a more general distribution in Guayana, coastal Guiana, Amazonia, 

 and Brasilia. All these reach middle altitudes on the Roraima sediments. 



In the Brazilian Highland and contiguous areas there is a second great center 

 of distribution in which some 80 to 90 species are to be found. There is here also 

 represented a high degree of restricted and broader endemism, and a residue of 

 species of general and widespread distribution. 



The two areas, then, that of Guayana to the north of the Amazon, and Bra- 

 silia to the south, are in many respects analogous, namely as to history, physiog- 

 raphy, and phyletic composition of the xyrid population. Very few identical 

 species as indicated above occur in both areas, but many instances of close intra- 

 specific relationships obtain. 



It is suggested that Xyris in South America, with its present bicentric dis- 

 tribution, may have occupied at one time an essentially identical and continuous 

 area, and that in subsequent history, by the intervention of the Amazon Basin, 



