Poa gracillima Vasey and its allies 



Charles Vancouver Piper 



The Poa species of the group related to P. graciUima Vasey 

 are separable with difficulty, "and distinguished only by slight 

 characters. They are characterized among the western poas by 

 their tufted habit, narrow flaccid leaves, loose open panicles, and 

 by their growing on cliffs. The 7 species may be distinguished 

 by the following key : 



Ligules of the sterile shoots obsolete or nearly so, those of the culm-leaves short and 



truncate. 



P. Mtdtiiomae. 



Ligules of all the leaves moderately developed, 1-2 mm. long. 



Low plants, ^-\o cm. high ; panicle small, usually purple, of few spikelets, the 



tays divaricate. 



P. vaseyochioa. 



Taller, TO-30 cm. high ; panicle with many spikelets, the rays not divaricate. 

 Panicle rather close; spikelets 6-9 mm. long; glumes of firm texture; 



blades flat. 



P^ saxatilis. 



Panicle loose ; spikelets 7 mm. long ; glumes thin ; blades involute. 



P. gracillima. 



Ligules of all the leaves rather long, 2-5 mm. long. 

 Panicle rather stiff, the rays short ; blades flat. 



Rays in about eight series of 3-5 each ; flowering glumes pubescent toward 



' the base. P* invagijiaia. 



Rays in about ^\^ series of I or 2 each ; flowering glumes minutely scabrous 



to the tip, puberulent at base.- P> actitiglumis^ 



Panicle loose, the rays somewhat drooping, in about five series of 2 or 3 each ; 



flowering glumes puberulent at base. P- alcea. 



It is very doubtful if all these species can be maintained. 

 Only careful field work and good series of specimens will enable 

 the problem to be solved. Poa vasey ochloa is probably only a 

 starved form of P. graciUima, from which P. saxatilis also isi 

 scarcely distinguishable. The ligule character may prove illusory,, 

 but larcre series of Poa alcea and P, Miiltnoinac indicate otherwise. 



' Poa Multnomae sp. nov. 



Sporobohis Bolanderi Vasey, Bot Gaz. 11: 337. 1886. Not 

 Poa Bolanderi N2.s^y, Bot. Gaz. 7: ^2. 1882. 



Perennial, densely tufted, with numerous slender innovations : 

 culms slender, 2- or 3-jotnted, often geniculate at base, terete, 



435 



