682 University of California Publications in Botany ['Vol. 8 



material, however, which has since been assigned to the species, even 

 by J. G. Agardh, does not in the least conform to this character. The 

 name has been used quite extensively to designate plants growing on 

 both the north Atlantic and the north Pacific shores. The original 

 illustration by Agardh in Icones algarum ineditae, 1821, pi. 13, 

 fig. 1, is of a fragment of a frond with complanate receptacles, and 

 was probably from an immature plant. This plate was reproduced by 

 Gardner in The genus Fucus on the Pacific Coast of North America, 

 1922, plate 1, figure 2. 



We have selected evanescens as the name best suited to include a 

 large aggregation of forms which appear in the northern portion of 

 our region, necessarily having to extend and modify Agardh 's original 

 description. 



Key to the Forms 



1. Typical mature fronds short, up to 15 cm 2 



1. Typical mature fronds over 15 cm. high 4 



2. Plants growing in salt marshes and tide flats 21. f. nanus (p. 698) 



2. Plants attached to rocks by a disk-shaped holdfast 3 



.3. Plants dendroid, segments usually much eroded 11. f. dendroides (p. 691) 



3. Plants flabellate, segments cuneate 20. f. cuneatus (p. 698) 



4. Average width of fronds less than 15 mm 5 



4. Average width of fronds more than 15 mm 12 



4. Average width of fronds unknown 18 



5. Midrib absent or indistinct 19. f. ecostatus (p. 697) 



5. Midrib distinct, usually percurrent 6 



6. Receptacles simple to deeply bifid, usually blunt 7 



6. Receptacles more or less decompound 10 



7. Receptacles with distinct margin free from conceptacles 



10. f. marginatus (p. 690) 



7. Receptacles without a free margin 8 



8. Receptacles widened suddenly, almost pedicellate.. 17. f. contractus (p. 695) 



8. Receptacles less conspicuously pedicellate 9 



9. Cryptostomata none or few 2. f. macrocephalus (p. 684) 



9. Cryptostomata 20-25 per square centimeter 18. f. oregonensis (p. 696) 



10. Fronds 4-5 mm. wide 16. f. angustus (p. 694) 



10. Fronds more than 5 mm. wide 11 



11. Receptacles more or less cornute 12. f. cornutus (p. 692) 



11. Receptacles not cornute 8. f. flabellatus (p. 689) 



12. Receptacles bi- tri-furcate, wide, spreading, acute. .6. f. stellatus (p. 687) 



12. Receptacles variously divided, not stellate 13 



13. Receptacles very large, tumid, mucilaginous 2. f. magnificus (p. 686) 



13. Receptacles narrower, mostly complanate, at times inflated or mucilaginous. ...14 



14. Receptacles complanate, up to 22 cm. long 9. f. longifructus (p. 689) 



14. Receptacles much shorter 15 



15. Receptacles with a distinct margin free from conceptacles... 5. f. robustus (p. 687) 



15. Receptacles without free margin 16 



16. Receptacles simple to deeply bifurcate, blunt ...3. f. pergrandis (p. 685) 



16. Receptacles variously branched acute or acuminate 17 



17. Cryptostomata absent or rare 13. f. rudis (p. 692) 



