2(1). Achene trigonous, the surfaces smooth or warty; ligule of short hairs 

 present 1. F. autumnalis. 



2. Achene not trigonous or only obscurely so, obovoid, the surfaces usually warty; 



ligule absent 2. F. miliacea. 



3(1). Ligule of short hairs present (this characteristic is most noticeable in those 

 entities that have broadly linear flattened leaf blades but is difficult 

 to detect in those extremes that have very involute narrow leaf 

 blades) (4) 



3. Ligule absent (9) 



4(3). A system of slender pale or reddish rhizomes present; robust perennials 

 with tall wandlike culms (5) 



4. Rhizomes absent or (if present) thickened and composed of stout contiguous 



culm-bases; perennial or annual species (7) 



5(4). Outer surface of spikelet scales uniformly pubescent; spikelets elliptic- 

 oblong, the apices of the bracts acutish and with the midrib ex- 

 serted as a prominent mucro; backs of leaf bases often pubescent 

 3. F. thermalis. 



5. Outer surface of spikelet scales glabrous or puberulent apically; spikelets 



ovoid to lance-ovoid, rarely oblong, the apices of the bracts rounded 

 with the midrib somewhat exserted; backs of the leaf bases seldom 

 pubescent (6) 



6(5). Fertile scales puberulent toward the tip; scapes usually flattened, often 

 scabrous-edged distally; edges of leaves (especially toward the tip) 

 scabrid; achene finely but definitely reticulate; in upper edges of 

 salt marshes, dune swales or fresh marshes on the Coastal Plain 

 4. F. caroliniana. 



6. Fertile scales usually smooth; scapes more slender, terete or broadly oval in 



cross section and smooth distally; edges of leaves usually not 

 scabrid; achene smoothish or with longitudinal rows of shallow 

 isodiametric pits; moist or wet prairies, river sloughs, marshes and 

 springy places in west Texas 11. F. puberula var. interior. 



7(4). Face (one side) of achene smoothish or with many (15 or more) longi- 

 tudinal row of shallow pits or cells (thus finely striate) 



5. F. tomentosa. 



7. Face (one side) of achene more closely reticulate, usually with 12 or less 



longitudinal rows of horizontally oriented rectangular cells (8) 



8(7). Perennial with spreading hard pale-green leaves; achenes lacking warts 



6. F. dichotoma. 



8. Annual with spreading or ascending leaves; achenes with warts 



7. F. annua. 



9(3). Low often densely tufted weedy annual; leaf blades linear-filiform 



8. F. Vahlii. 



9. Taller more robust wider-leaved perennials (10) 



10(9). Plants densely cespitose; bases of leaves hard, leathery, usually very dark- 

 brown or castaneous, often quite lustrous, deeply set in substrate; 

 common to brackish coastal habitats 9. F. castanea. 



10. Plants in small tufts or culms solitary; bases of leaves thickened and hard 



or culm bases bulbous but in any case more shallow-set in sub- 

 strate; either with stout contracted rhizomes or with fasciculate 

 clusters of narrow orange-brown rhizomes; from sandy acid pine- 

 land savannahs or oak barrens to heavy prairie soils but not in 

 brackish coastal habitats (1 1) 



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