2 CONTRIBUTIONS PROM THE NATIONAL HERBARIUM. 



DESCRIPTION. 



Perennials or sometimes apparently annuals with erect or creeping culms and 

 flat, usually broad, sometimes petioled leaf blades. Inflorescence paniculate, 

 the open or contracted panicles terminal and axillary, the spikelets usually in 

 pairs, unequally short-pediceled along the stiffly spreading or ascending main 

 branches, or rarely single in an open panicle. Spikelets with keeled glumes, 

 thus appearing somewhat laterally compressed, similar in structure to those 

 of Pamcum, the glumes and sterile lemma usually rather strongly nerved, 

 and commonly ending in an apiculation or convolute point. First glume 

 usually more than half as long as the spikelet, clasping, 3-nerved, the second 

 glume and sterile lemma about equal, longer than the fruit, 5-nerved, the 

 lemma inclosing a membranaceous palea and rarely a staminate flower ; fertile 

 lemma usually acute or acutish, indurate, dorsally compressed, usually raised 

 on a short stipe, the margins usually flat but in our species more or less 

 inrolled, the base bearing on either side membranaceous appendages adnate 

 to the lemma below, free above, the appendages in many of our species obso- 

 lete and indicated only by minute scars or excavations; palea entirely inclosed 

 in the margins of the lemma. 



Abnormal specimens occur, especially in nos. 2 to 4, in which the sterile 

 lemmas are greatly multiplied, forming elongate curved spikelets, as much as 

 2 cm. long. 



KEY TO THE SPECIES. 



Appendages of fertile lemma well-developed wings. 



Blades widest near the cordate base 9. I. mexicanus. 



Blades narrowed toward the base, this not cordate. 



Sheaths densely long-villous 8. I. leiocarpus. 



Sheaths glabrate or somewhat pilose. 



Blades lanceolate-linear, many times longer than wide; spike- 

 lets long-pediceled 10. I. ichnodes. 



Blades lanceolate-elliptic, not more than 6 times longer than wide. 



7. I. nemoralis. 

 Appendages of fertile lemma reduced to scars. 



Blades petiolate, the petiole 1 to 15 mm. long ; first glume acute, about half 

 as long as the spikelet. 

 Spikelets 3 mm. long ; culms delicate, spreading, much branched ; 



blades not over 6 mm. wide 1. I. mayarensis. 



Spikelets 3.5 to 4 mm. long ; culms erect, simple or sparingly branched ; 



blades 1 to 3 cm. wide 6. I. lanceolatus. 



Blades more or less clasping, often oblique at base, usually over 1 cm. wide. 



Glumes with attenuate tips, usually exceeding the sterile lemma and 



floret ; blades thin, more or less pilose. 



Spikelets with a few long stiff hairs near the margin toward the 



summit of both glumes; plants delicate; blades rarely over 



4 cm. long and 1 cm. wide 2. I. tenuis. 



Spikelets glabrous^ or scabrous on the midnerves only; blades up 



to 7 cm. long and 2 cm. wide 3. I. nemorosus. 



Glumes acute or acuminate but not attenuate, the first shorter than 

 the spikelet; blades firmer. 



Blades lanceolate, 1 to 2 cm. wide, glabrous 4. I. pallens. 



Blades oval to ovate-lanceolate, 1.5 to 3.5 cm. wide, often pubes- 

 cent beneath 5. I. axillaris. 



