1925] Setchell-Gardner: Melanophyceae 621 



FAMILY 21. LESSONIACEAE fam. nov. 



Fronds more or less compound, composed of holdfast, branching 

 stipe and few to numerous blades; structure as in Laminariaceae; 

 mucilage ducts present or absent ; blades destitute of cryptostomata 

 or tufts of hairs; paraphyses unicellular, with hyaline appendages. 



We have included under the family Lesson iaceae all those members 

 of the Laminariales in which a distinct division of stipe and frond 

 occurs by a splitting (rather than disintegration, e.g., schizogenetic 

 rather than lysigenetic) process in the principal region of growth, i.e., 

 at the transition place. With one exception (Lessoniopsis), there are 

 no outgrowths arising at the transition place as in the Alariaceae. 



Key to the Tribes 



1. Sori on distinct sporophylls arising as outgrowths (alarioid) at the transition- 

 place 3. Lessoniopseae (p. 631) 



1. Sori on the ordinary blades 2 



2. Stipe regularly dichotomous 1. Lessonieae (p. 621) 



2. Stipe scorpioid sympodial 2. Macrocysteae (p. 626) 



TRIBE 1. LESSONIEAE setchell 



Members of the family of the Lessoniaceae with regularly dicho- 

 tomous stipes, but without specialized sporophylls. 



Setchell, Kelps of the U. S. and Alaska, 1912a, p. 157. 



Key to the Genera 



1. Stipe flattened, solid, blade reticulately ribbed 49. Dictyoneurum (p. 621) 



1 . Stipe swollen, hollow; blade plane or longitudinally grooved 2 



2. Main stipe swollen at summit into a pneumatocyst 



50. Nereocystis (p. 623) 



2. Main stipe cylindrical to the apex 51. Postelsia (p. 624) 



49. Dictyoneurum Rupr. 



Original stipe very short, attached by branched hapteres, at first 

 erect, later becoming decumbent, much flattened and thin, developing 

 hapteres along the margins and later dying and disappearing as the 

 anterior portion advances, meristem at the advancing end of the flat- 

 tened prostrate stipe becoming erect and splitting dichotomously, 

 finally dividing the blade longitudinally into two equal parts; original 

 blade and often the mature later blades with distinct "midrib" and 

 reticulate alae, later the "midrib" disappearing more or less and the 

 blade becoming reticulated with coarse ribs ; sori on both sides of 

 blade, irregular, broad. 



