210 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Pennisetum has been divided into various subgenera which appear 

 to be fairly natural groups. Among our few species, however, are 

 some that are intermediate or exceptional. Pennisetum, setosum, with 

 its densely plumose bristles, comes under subgenus Erioclmda, but 

 the obviously related P. antillarum has bristles not at all plumose. 

 The introduced species belong in Pennisetum proper, with ciliate 

 bristles and more than one spikelet in a fascicle. Pennisetum 

 Izarwinslcyi falls in this group, though in this the bristles are some- 

 times scarcely ciliate. The rest of our species, with bristles scabrous 

 only, belong in subgenus Gymnothrix. The section Becke.ropsis of 

 the subgenus Gymnothrix is not represented in America, though the 

 South American P. exaltatum and P. mutilatum, with few and reduced 

 bristles, approach it. Pennisetum glaucum is placed in section 

 Penicillaria by Stapf 2 and by Leeke. The name Penicillaria refers 

 to the minute brush of hairs at the tips of the anthers in this species. 



An adequate revision of Pennisetum as a whole can be prepared 

 only by someone having access to abundant material from Africa, 

 its center of distribution. The present paper deals only with the 

 speeies found in North America, 10 native and 4 introduced. 



The text figures illustrate part of the inflorescence, two-thirds 

 natural size. 



DESCRIPTION OF THE GENUS AND SPECIES. 



PENNISETUM I,. Rich. 



Pennisetum L. Rich, in Pers. Syn. PI. 1: 72. 1805. Five species, P. typhoideitm, 

 P. setosum, P. cenchroides, P. orientate, and P. violaceum are included. All belong 

 to the genus as at present limited. The first (which is the same as P. glaucum), 

 agreeing with the generic characters given and being an important economic species, 

 is taken as the type. The generic name refers to the plumose bristles, a character 

 more pronounced in the other species included than in the type. 



Penicillaria Willd. Enum. PI. 1036. 1809. Penicillaria spicala Willd., based on 

 Holcus spicatus L. (which is the same as Pennisetum glaucum), is taken as the type. 

 In a footnote Willdenow explains that the genus was characterized by Swartz in 

 Schrader's Neues Journal. The article referred to is one in which Swartz 3 discusses 

 the genus Holcus and shows that //. spicatus L. does not belong in that genus, but 

 rather in Cenchrus or in a distinct genus. He then gives a detailed description from a 

 specimen grown in his garden, but does not propose a generic name. A second species, 

 P. ciliata, based on Alopecurus indicus (Pennisetum indicum (Murray) Kuntze) ia 

 added. The name doubtless refers to the penicillate tips of the anthers, but neither 

 Swartz nor Willdenow mentions this character. 



Gymnothrix Beauv. Ess. Agrost. 59. pi. IS. f. 6. 1812. A single species, G. thuarii 

 Beauv., from Ile-de-France [Mauritius] is included. The figure shows a fascicle 

 with bristles not plumose. Beauvois divides Pennisetum into three genera: Penicil- 

 laria, containing the species with penicillate anthers ("apici villosis"); Pennisetum, 



2 In Thiselt. Dyer, Fl. Cap. 7: 431. 1898. 

 3 Neu. Journ. Bot. Schrad. 2: 39-49. 1807. 



