HOW TO KNOW THE GRASSES 



TRIBE XI. PANICEAE 



la. Spikelets inclosed in spiny burs. Fig. 282. 



FIELD SANDBUR Cenchrus paucifiorus Benth. 



Figure 282 



Annual; culms 20 — 90 cm. long, usually 

 spreading and making mats. The spike- 

 lets are mostly concealed by the horribly 

 spiny burs, which are made up of sterile 

 branches. The burs are borne in short 

 spikes along a zig-zag rachis, and fall off 

 at a touch when ripe. The spines of the 

 burs are very sharp, and each spine is 

 microscopically backwardly-barbed. These 

 spines can inflict painful and dangerous 

 flesh wounds. Each bur contains one to 

 several spikelets, which resemble those of 

 species of Panicum. Sandbur is on unde- 

 sirable weed of disturbed soil, much more 

 common on sandy land than on heavier 



soils. Where it is abundant, it may furnish some feed for livestock 



when young. May — October. 



Cenchrus tribuloides L. (DUNE SANDBUR) has larger burs, 10—17 



mm. in diameter. It grows on dunes along the Atlantic and Gulf Coasts. 



lb. Spikelets not inclosed in spiny burs 2 



2a. Spikelets imbedded in one side of an erect, unbranched, flattened, 

 corky rachis. Fig. 283. 



ST. AUGUSTINE GRASS Stenotaphrum secundatuzn (Walt.) Kuntze 



Perennial; plants spreading rapidly and ex- 

 tensively by stolons; erect flowering stems 

 10 — 30 cm. tall. The leaf sheaths are very 

 much flattened and keeled; blades with round- 

 ed, blunt tips. The spikelets are similar to 

 those of Panicum species, but are nearly hid- 

 den by the flanges of the rachis. The first 

 glume and sterile lemma are exposed This 

 unique grass is used for lawns in some locaU- 

 ties in the South. Occasionally plants occur 

 with white-striped leaf blades, and these may 

 be cultivated for ornament. June — September. 



Figure 283 



2b. Spikelets not sunken into the rachis 3 



149 



