THE NOETH AMEEICAN SPECIES OF ISACHNE. 



By A. S. Hitchcock. 



INTRODUCTION. 



This tropical genus of grasses is, in technical characters, anomalous 

 in the tribe Paniceae, to which it belongs, in that the spikelet has 

 two fertile florets instead of one. That is, throughout the tribe, 

 with the exception of Isachne, the spikelet has one terminal fertile 

 floret and one sterile floret, this consisting of a lemma only, of a lemma 

 and palea, or of a lemma, palea, and a staminate flower. In Isachne 

 the lateral floret contains a perfect flower and normally develops a 

 seed. 



There are seven species in North America, a few more in South 

 America, and several in the tropics of the Old World. 



DESCRIPTION OF THE GENUS AND SPECIES. 



ISACHNE R. Br. 



Isachne R. Br. Prodr. Fl. Nov. Holl. 196. 1810. A single Australian species, 

 I: australis, is described. 



DESCRIPTION. 



Perennial or rarely annual grasses with simple or usually branching stems, flat, 

 strongly nerved blades, and paniculate inflorescence. Spikelets obovoid to sub- 

 globose. Glumes membranaceous, about equal and as long as the fruits or at maturity 

 exceeded by them. Lower floret perfect or staminate, its lemma and palea indurate 

 and similar in form and texture to those of the upper floret. Both florets (or fruits) 

 plano-convex, obtuse, equal in size or the upper shorter, the pair usually remaining 

 attached by the minute rachilla joint between them. 1 



Isachne -polygonoides is exceptional in that the lower floret is unlike the upper. In 

 all the species the lower floret of some of the spikelets may fail to perfect a grain. 

 When sterile the floret is often longer and the lemma less convex than when fertile, 

 the spikelets on the same panicle thus having a somewhat diverse appearance. 



KEY TO THE SPECIES. 



Florets appressed-pubescent. 



Blades ovate-clasping 1 . I. polygonoides. 



Blades linear 2. I. leersioides. 



1 For further discussion see Chase, Genera Paniceae. IV. Proc. Biol. Soc. Washing- 

 ton 24: 149. 1911. 



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