Vol. 10, No. 1 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN July 1, 1958 



THE BOTANY OF THE GUAYANA HIGHLAND— PART III 



Bassett Maguire and John J. Wurdack 

 and Collaborators 

 introduction 



In Part III we continue to report on plant collections made in South Ameri- 

 can Guayana. No additional field work has been done since the preparation of 

 Part II* of this series. However, at this writing we are making ready for immi- 

 nent return to the region of the Casiquiare, and the Rios Pacimoni and Yatua 

 in Amazonian Venezuela. There we are again to visit Cerro de la Neblina and 

 the immediately outlying tabular mountains, all of the Roraima sedimentary 

 complex. This, the nineteenth of our Guayana expeditions, is expected to be in 

 the field for some six months. Field work and publication continue with the 

 assistance of the National Science Foundation. 



Of the studies presented herein, those of the Xyridaceae, Rapateaceae, and 

 Gutti ferae have been made by Maguire, and of the Melastomataceae by AVurdack. 

 Contributions of collaborators are as follows: Leguminosae and Butaceae, Rich- 

 ard S. Cowan; Myrtaceae, Rogers MeYaugh ; Combretaeeae, B. Maguire and A. 

 AY. Exell; Apocynaceae, Joseph Monachino ; and Bignoniaceae, N. Y. Sandwith. 

 Sherwin Carlquist presents Part II of the "Anatomy of Guayana Mutisieae." 



Illustrations have been prepared by Charles C. Clare, Alexis Khoury, Walter 

 L. Graham, and Richard S. Cowan. 



XYRIDACEAE 



Traditionally, two genera have been recognized as constituting the small 

 family Xyridaceae: Xyris with numerous species widely distributed in the 

 Western Hemisphere, Europe, Africa, and Australia, and Abolboda with com- 

 paratively few species confined to tropical South America (exclusive of Andea). 

 Both have been recognized as homogeneous genera except for the anomalous 

 Abolboda sceptrum, for which until recently there has been insufficient material 

 for adequate diagnosis. 



Im Thurn on his Roraima expedition (1884-1885) collected the upper por- 

 tion of a single flowering scape. Upon this specimen Oliver established the name 

 Abolboda sceptrum. 1 Later, McConnell and Quelch 2 (1894, 1898) succeeded in 

 collecting only adult leaves and young plants. Apparently the plant was not 

 again collected until Tate in 1928 obtained single specimens of flowering and 

 fruiting plants from Cerro Duida. 3 Of these specimens, Malme, prominent stu- 

 dent of the Xyridacf ae who reviewed Tate's material, wrote, in part, "forsitan 

 novum genus sistat." 



Subsequently, no fewer than 26 collections of A. sceptrum and its segregates 

 have been made. Ample opportunity has been had to study the several popu- 

 lations in the field. It has now become abundantly demonstrable that the plants 

 known as A. sceptrum must be referred to a distinct genus, for which I propose 

 the name Orectanthe (descriptive of the porrect flowers). 



On palynological evidence, Erdtman 4 has suggested that Abolboda and Xyris 



*The botanv of the Guayana Highland— Part II. Mem. N. Y. Bot. Gard. 9: 235-392. 1957. 



1 Trans. Linn. Soc. II. Bot, 2: 286. 1887. 



2 Trans. Linn Soc. II. Bot. 6: 69. 1901. 



3 Bull. Torrey Club 58: 326. 1931. 



4 Pollen morphology and taxonomy 453, 454. 1952. 



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