48 Allan Hancock Pacific Expeditions vol. 26 



18. Cortical cells arranged in distinct horizontal and vertical 



rows in lower two-thirds of nodes 



C. recticorticum Dawson 



18. Cortical cells not arranged in vertical rows 19 



19. Branching sympodial C. sympodiale Dawson 



19. Branching dichotomous or irregular, but not sympodial 20 



20. Outer cortical cells of nodal band separated into two 

 groups by a horizontal clear space usually at about the 

 lower third of the node; tetrasporangia involucrate 21 



20. Outer cortical cells of nodal band not clearly divided 

 into two groups; tetrasporangia immersed, involucrate 

 or naked 23 



21. Nodes of most filaments each bearing, at first abaxially, a 

 short, thick, apically rounded, unicellular hair, or these later 



sometimes whorled C. fimbriatum S. & G. 



21. Nodes without such a specialized hair 22 



22. Cells of lower portion of divided cortical band distinctly 



and persistently elongated horizontally 



C. gracillimum v. byssoideum (Harv.) Feldm.-Maz. 



22. Cells of lower portion of divided cortical band, except 

 in young stages, angular, small and not distinctly 



horizontally elongated C. taylorii Dawson 



23. Tetrasporangia immersed, not individually prominent or 



projecting, although the nodes may be tumid 24 



23. Tetrasporangia naked or involucrate, projecting 30 



24. Plants procumbent, with conspicuous opposite branching 



in lower parts C. procumbens S. & G. 



24. Plants erect or entangled, without conspicuous opposite 



branching 25 



25. Cortical bands narrow, usually less than half as high as wide, 



with a central row of large cells bordered by small ones 



C. marshallense Daws. 



25. Cortical bands thicker, more than half as high as wide, the 



cells ± uniform 26 



26. Axes 140-200 p. in diam.; cortication relatively complete, 



the nodal bands covering most of axes 



C. sinicola S. & G. (in part) 



26. Axes 80-130 p. in diam.; nodal cortication truncated 



above and below, the ecorticate internodes prominent .... 27 

 27. Tetrasporangial nodes tumid, providing a strongly banded 



effect to axes; sterile tips non-forcipate 28 



27. Tetrasporangial nodes not tumid, the fertile areas swollen 



but not strongly banded; sterile tips forcipate 29 



