MANUAL OF THE GRASSES OF THE UNITED STATES 



735 



— Sandy open ground, often a weed 

 in sandy fields, Ontario to Oregon, 

 south to Florida, Texas, and Cali- 

 fornia; Mexican plateau; coastal re- 

 gion of tropical America; southern 

 South America. The type, from Baja 

 California, is a small arid-ground 

 specimen, the burs smaller than those 

 of plants of more favorable situations. 

 Specimens with long spines have been 

 differentiated as C. albertsonii Run- 

 yon and C. longispinus (Hack.) Fer- 



nald. The spikelets are identical ex- 

 cept in size. 



7. Cenchrus tribuloides L. Dune 

 sandbur. (Fig. 1121.) Stouter than 

 C. pauciflorus; soon branching and 

 radiate-decumbent, rooting at the 

 nodes; sheaths usually much overlap- 

 ping; burs (excluding spines) 5 to 6 

 mm. wide and 8 to 9 mm. high, usu- 

 ally conspicuously villous. O — In 

 loose sands of the coast, Staten Is- 

 land, N. Y., to Florida and Louisiana; 

 West Indies. 



146. AMPHICARPUM Kunth 



{Amphicarpon Raf.) 



Spikelets of 2 kinds on the same plant, one in a terminal panicle, perfect 

 but not fruitful, the other cleistogamous on slender leafless subterranean 

 branches from the base of the culm or sometimes also from the lower nodes; 

 first glume of the aerial spikelets variable in size, sometimes obsolete; second 

 glume and sterile lemma about equal; lemma and palea indurate, the margins 

 of the lemma thin and flat ; fruiting spikelets much larger, the first glume want- 

 ing; second glume and sterile lemma strongly nerved, subrigid, exceeded at 

 maturity by the turgid, elliptic, acuminate fruit with strongly indurate lemma 

 and palea, the margins of the lemma thin and flat; stamens with small anthers 

 on short filaments. Annual or perennial erect grasses, with flat blades and 

 narrow terminal panicles. Type species, Milium amphicarpon Pursh (Amphi- 

 carpum purshii). Name from Greek amphikarpos, doubly fruit-bearing, allud- 

 ing to the two kinds of spikelets. 



Blades conspicuously hirsute 1. A. purshii. 



Blades glabrous or nearly so 2. A. muhlenbergianum. 



1. Amphicarpum purshii Kunth. 

 (Fig. 1122.) Annual; culms erect, 30 

 to 80 cm. tall, the leaves crowded 

 toward the base, hirsute; blades erect, 

 10 to 15 cm. long, 5 to 15 mm. wide, 

 sharp-pointed; panicle 3 to 20 cm. 

 long; spikelets elliptic, 4 to 5 mm. 

 long; subterranean spikelets 7 to 8 

 mm. long, plump, acuminate. O 

 (Amphicarpon amphicarpon Nash.) — 

 Sandy pinelands, New Jersey to 

 Georgia. 



2. Amphicarpum muhlenbergia- 

 num (Schult.) Hitchc. (Fig. 1123.) 

 Perennial; culms usually decumbent 

 at base, 30 to 100 cm. tall; leaves 

 evenly distributed; blades firm, 

 white-margined when dry, mostly less 

 than 10 cm. long, 5 to 10 mm. wide; 

 panicle long-exserted, few-flowered; 

 spikelets narrowly lanceolate, 6 to 7 



mm. long ; subterranean spikelets 6 to 

 9 mm. long. % (A. floridanum 

 Chapm.) — Low pinelands, South Car- 

 olina and Florida. 



147. OLYRA L. 



Plants monoecious; inflorescence 

 paniculate; pistillate spikelets borne 

 on the ends of the branches of loose 

 panicles, the smaller staminate spike- 

 lets pedicellate below the pistillate 

 ones, sometimes the upper branches 

 all pistillate and the lower ones all 

 staminate; pistillate spikelets rather 

 large; first glume wanting; second 

 glume and sterile lemma herbaceous, 

 often caudate-acuminate; fruit bony- 

 indurate; staminate spikelets readily 

 deciduous; glumes and sterile lemma 

 wanting, the lemma and palea mem- 



