Vol. 35, pp. 81-88 May 26, 1922 



PROCEEDINGS 



or THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



DESCRIPTIONS OF NEW ORCHIDS FROM TROPICAL 

 AMERICA WITH NOMENCLATORIAL CHANGES. 



BY OAKES AMES. 



In further study of the orchids of tropical America, the fol- 

 lowing plants appear to deserve recognition as new species or 

 to require nomenclatorial attention. 



Aa Rosei, sp. nov. 



Similitudinem gerit cum Aa MaUheivsio (Reichb. f.) Schltr. Herba 

 gracilis. Caules erecti, vaginis scariosis arete adpressis vestiti. Racemus 

 densiflorus, cylindraceus. Bracteae albidae, acutae. Sepala lateralia 

 glabra, oblonga, obtusa, uninervia. Sepalum dorsale ovatum, glabrum, 

 obtusum, uninervium. Petala oblongo-elliptica, obtusa, uninervia. 

 Labellum subgloboso-cucuUatum, ostio valde contractum, marginibus 

 basi excepta minute fimbriatulum, basi utrinque glandula ornatum. 

 Columna brevis. 



Roots fleshy, up to 5 mm. in diameter when dry. Leaves wanting at 

 flowering time. Stems slender, 30-35 cm. tali, 1-3 mm. thick, invested 

 with whitish closely appressed sheaths. Raceme about 4 cm. long, 5-6 

 mm. in diameter, cylindrical, many flowered. Floral bracts whitish, trans- 

 lucent, triangular-lanceolate, acuminate, acute. Rhachis puberulous, 

 hairs flaccid, whitish. Pedicel abbreviated, together with the ovary 2 mm. 

 long. Flowers more or less globose, crowded. Lateral sepals 2.25 mm. 

 long, 1 mm. wide, oblong, concave, with a conspicuous mid-nerve, smooth. 

 Upper sepal 2 mm. long, L25 mm. wide at base, triangular-ovate, obtuse, 

 one-nerved. Petals about 2 ram. long, oblong-elliptic, obtuse, conspicu- 

 ously one-nerved. Labellum 2.5 mm. long, subglobose-cuoullate, margin 

 fimbriate beyond the middle, basal margin entire; near the base a large 

 gland is situated on each side. Column minute, dilated upward. 



From the closely related Aa macra Schltr. this species differs in the 

 smaller flowers, broader petals and shorter stems. 



PERU, Cuzco. Mr. & Mrs. J. N. Rose 19039. September, 1914. 

 (Type in United States National Herbarium 761630.) 



17— Proc. Biol. Soc. Wash., Vol. 3o, 1922. (81) 



