392 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



76. SPOR0BOLUS R. Br. Dropseed 



Spikelets 1 -flowered, the rachilla disarticulating above the glumes; 

 glumes 1-nerved, usually unequal, the second often as long as the 

 spikelet; lemma membranaceous, 1-nerved, awnless; palea usually 

 prominent and as long as the lemma or longer; caryopsis free from 

 the lemma and palea, falling readily from the spikelet at maturity, 

 the pericarp free from the seed, usually thin and closely enveloping 

 it, but readily slipping away when moist. Annuals or perennials, 

 with small spikelets in open or contracted panicles. Type species, 

 Sporobolus indicus. Name from Greek spora, seed, and ballein, to 

 throw, alluding to the free seeds. In some species of this genus the 

 palea splits at maturity, giving the impression of extra lemmas. 

 The first glume is early deciduous in some species. The size of the 

 spikelets is often variable in the same panicle. 



Most of the perennial species are palatable forage grasses, but few 

 of the them are abundant enough to be of importance. Two species 

 of the Southwest, S. airoides and S. wrightii, are valuable grasses in 

 the arid and semiarid regions; S. interruptus is common on the Arizona 

 Plateau; and the widely distributed S. cryptandrus is also important. 

 The seed of S. flexuosus and S. cryptandrus have been used for food 

 by the Indians. 



la. Plants annual. 



Panicle narrow, few-flowered, spikelike. 



Lemma pubescent 6. S. vaginiflorus. 



Lemma glabrous 7. S. neglectus. 



Panicle open, many-flowered. 



Pedicels very short, appressed; glumes glabrous 1. S. ramulosus. 



Pedicels elongate, spreading; glumes usually sparsely pubescent. 



2. S. MICROSPERMUS. 



lb. Plants perennial. 



2a. Plants producing creeping rhizomes. Panicle narrow or spikelike. 



Rhizomes extensively creeping; leaves numerous, crowded, the blades invo- 

 lute, conspicuously distichous; panicle spikelike 3. S. virginicus. 



Rhizomes short; leaves not numerous nor crowded nor involute; panicle 



narrow but loose 9. S. macrus. 



2b. Plants without creeping rhizomes. 



3a. Glumes nearly equal, much shorter than the lemma. Panicle narrow or 

 spikelike. 

 Panicle branches short and appressed, the panicle spikelike. 



4. S. POIRETTI. 



Panicle branches slender, ascending, the panicle scarcely spikelike. 



5. S. INDICUS. 

 3b. Glumes unequal or if equal as long as the spikelet. 



4a. Spikelets mostly 3 to 7 mm long. Plants usually less than 1 m tall. 

 Second glume shorter than the lemma; panicle contracted, more or less 

 included in the sheath. 



Lemma glabrous, the palea not exceeding it .---.--- 8 - S. asper. 



Lemma pubescent, the palea acuminate, exceeding it. 



10. S. CLANDESTINUS. 



Second glume about as long as the lemma; panicle open (contracted in 

 S. purpurascens) , not included. 

 Branches of the narrow panicle in distinct whorls, usually less than 

 4 cm long. 

 Branches 2 to 3 cm long, somewhat distant, more or less spreading, 



the panicle open 16. S. gracilis. 



Branches 1 to 2 cm long, ascending or appressed, overlapping, the 



panicle contracted 17. S. purpurascens. 



Branches of the open panicle not in distinct whorls, usually more than 

 4 cm long. 



