THE NOKTH AMERICAN SPECIES OF BRACHIAEIA. 



By Agnes Chase. 



INTRODUCTION. 



The group of grasses here discussed was until recent years com- 

 monly included in the genus Panicum. Although the genus Brachi- 

 aria was proposed in 1853, it was not accepted as valid until 1901. 

 This is because its most distinctive character was overlooked — that 

 of reversed spikelets (that is, spikelets with the back of the fertile 

 lemma turned away from the axis instead of toward it, as in P asp alum 

 and in the few species of Panicum having racemose inflorescence). 

 As a section of Panicum, Brachiaria had been made to include a num- 

 ber of heterogeneous species, now referred to five distinct genera, 

 on the one common character of racemose inflorescence. 



From Eriochloa and Acconopus, in which also the spikelets are 

 reversed, Brachiaria differs in having a well-developed first glume. 

 From the first it differs also in the unspecialized lower rachilla joint, 

 which in Eriochloa is enlarged, and from the second in the turgid 

 spikelets and the racemose instead of digitate arrangement of the 

 racemes. 



Brachiaria is one of the few genera of Paniceae which belong 

 chiefly to the Old World. 



The text figures, drawn by the author, illustrate part of the 

 inflorescence, one-half natural size, and two views of the spikelet 

 and one of the fruit, magnified 10 diameters. In each case the 

 specimen from which the drawing was made is indicated. 



HISTORY OF THE GENUS. 



The genus Brachiaria Griseb. 1 is based on " Panicum sect. 

 Brachiaria Trim," and a single species, B. erucaeformis (J. E. 

 Smith) Griseb., is included. Grisebach cites, not the first work 2 in 

 which Trinius proposes the section Brachiaria, but a later work, 

 Panicearum Genera, 3 in which Trinius includes a somewhat differ- 

 ent group of species from those included in his first work. In 



'In Ledeb. Fl. Ross. 4: 469. 1853. 



2 Gram. Pan. 51, 125. 1826. 



8 Mem. Acad. St. Petersb. VI Sci. Nat. 3 2 : 194. 1834. 



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