1918] The Grasses of Illinois 351 



26. SPOROBOLUS R. Br. 

 Dropsccd. Rush Grass 



The species of this genus found in Illinois are all native to the 

 state and include both annuals and perennials. They all grow in dry 

 soil and nearly all have narrow, involute, pointed leaves. The ligules 

 are membranous, from 1 to 3 mm. long. The spikclcts are one-flowered 

 and the fruit is not inclosed by the lemma, but is free and usually falls 

 out as soon as ripe. 



a. Panicle diffuse, branches capillary. S. asperifolius 



aa. Panicle not diffuse, branches slender but not capillary. 



b. Glumes very unequal; panicle branches ascending or spreading, panicle 

 not spike-like (except secondary panicles in autumn). 

 c. Sheaths not bearded at the summit; spikelets 4 to 6 mm. long. 



S. heterolepis 

 cc. Sheaths conspicuously bearded at the summit; spikelets 2.5 to 3 

 mm. long. S. cryptandnis 



bb. Glumes nearly equal; panicle contracted, more or less spike-like. 



c. Sheaths much enlarged and always inclosing the lateral panicles, 

 sometimes the terminal ones ; blades short, scarcely longer than the 

 sheaths, 

 d. Spikelets 2.5 to 3 mm. long; lemma not pubescent. S. neglecius 

 dd. Spikelets 3.5 to 4 mm. long; lemma pubescent. S. vagivaeflorus 

 cc. Sheaths never enlarged, except the upper which often partially in- 

 closes the panicle; blades long, very much longer than the sheaths, 

 always very narrow and involute; plants perennial, 

 d. Spikelets 5 mm. or more long; panicles densely flowered and 

 usually included in the enlarged upper sheaths, 

 e. Lemma and palea pubescent at tlje base. 



f. Palea with a long sharp point; lemma about two-thirds 



the length of the palea. S. clandestinus 



ff. Palea acute but not with a long sharp point, and only 



slightly longer than the lemma. S. canovirens 



ee. Lemma and palea never pubescent at base, but always smooth 



and polished. S. asper 



dd. Spikelets never more than 4 mm. long; panicles loosely flowered 



and not included in the upper sheath. S. drnmmondii 



Sporobolus asper (Michx.) Kunth 

 Long-leaved Rush Grass (Fig. 155) 



Sporobolus longifolius, Britton '07, 105. 



Culms 1.5 to 4 feet tall, smooth; sheaths smooth; blades 4 to 18 

 inches long, 2 to 4 mm. wide, flat at base but soon becoming involute, 

 smooth on the under surface, rough on the upper, and with long hairs 

 near the base ; panicle partially included in the upper sheath, 3 to 9 

 inches long, about half an inch wide ; spikelets 5 to 6 mm. long. 



This species is found in dry, usually sandy soil. S. drummo7idn 

 closely resembles this species, but it has smaller spikelets, narrower 

 and less dense panicles which are usually not inclosed in the sheath. 



ILLINOIS SPECIMENS : Without locality, TJ'o?/ in 1882. champaign CO. With- 

 out locality, Seymour, Oct., 1880; St. Joseph, Clinton, Oct., 1895; Champaign, 

 Clinton, Oct., 1895; Urbana, Gates, Oct., 1907. cook co. Chicago, Vmbach, Sept., 



