560 University of California Publications in Botany [ VoL - 8 



The genus Desmarestia is well represented on the Pacific coast of 

 North America, extending in its various species from the Bering Sea 

 on the north to Santa Catalina Island off the coast of southern Cali- 

 fornia on the south, so far as is known of its distribution at present. 

 The species of both the ligulate and the filiform groups manifest a 

 degree of variability which has up to date made it exceedingly difficult 

 to determine specific limits. It is evident from the relatively good 

 supply of herbarium material at our disposal, that more than mere 

 superficial resemblances must be resorted to in order to make a satis- 

 factory disposition of the group. Knowledge of the entire life-history 

 is highly essential. Little is known of reproduction. The character 

 of the hairs, present only in the early stages of growth — absent in 

 most of our herbarium specimens — is, so far as our experience shows, 

 of marked constancy and would doubtless be of decided assistance in 

 classification. The histological structure, very difficult to restore after 

 the material has once been thoroughly dried, certainly will prove of 

 decided value in establishing specific entities when studied in fresh 

 material. 



"We have made use of all of these different phases as far as the 

 material and time at our disposal permits and have come to the follow- 

 ing conclusions regarding the number, arrangement, and distribution 

 of the Pacific coast species. 



Key to the Species 



1. Fronds filiform and either terete or compressed 2 



1. Fronds ligulate or membranaceous (Herbaceae) 6 



2. Fronds terete or in part subterete, branching mostly opposite (Virides) .... 3 

 2. Fronds compressed or subterete below, branching mostly alternate 



(Aculeatae) 5 



3. Fronds profusely branched; tylloses few or wanting 4 



3. Fronds moderately branched; tylloses filling central tube to near tip 



3. D. farcta (p. 562) 



4. Branches long, attenuated, successive orders gradually reduced in 



s i ze 1. D. media (p. 561) 



4. Branches slightly attenuated, blunt, successive orders abruptly changing 



to smaller size 2. D. pacifica (p. 562) 



5. Fronds up to 15 dm. high and 3 mm. wide, with aculeate margins, moderately 



branched 4. D. latifrons (p. 563) 



5. Fronds up to 7 dm. high and 1.5 mm. wide, with smooth margins and profusely 



branched 5. D. intermedia (p. 564) 



6. Fronds unbranched or with a few short branches at the base 



10. D. foliacea (p. 569) 



6. Fronds regularly branched 7 



7. Fronds membranaceous, up to 1 m. wide 9. D. latissima (p. 568) 



7. Fronds ligulate, up to 1 dm. wide 8 



8. Fronds more than 3 m long with prominent aculeae along the margins 



8. D. munda (p. 567) 



8. Fronds less than 3 m. long, smooth or with fine aculeae along the margins.. 9 



