ECOLOGY AND TAXONOMY OF HttUmeda 



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Plants flaccid, straggling and decumbent, sometimes to over 1 m long; 

 holdfast attachment not restricted to a single basal region but at several 

 places where the sprawling thallus contacts substrate; calcification moderate 

 to heavy; the surface usually glossy; branching sometimes sparse but usually 

 frequent with up to five branches arising from a single segment; segments 

 ribbed, chalky to brittle, at times subcylindrical but more commonly 

 subcuneate to reniform, the upper margin entire, undulate or lobed, to 9 mm 

 long, 15 mm broad, and averaging 0-50-0-75 mm in thickness. 



Cortex of two, sometimes three, layers of utricles, these generally produced 

 by dichotomies in the lateral branches of the medullary filaments; outermost 



Fig. 44b. H. gracilis showing a more compact, broader segmented habit than that in 

 Fig. 44a. Both are relatively common. Specimen from Mentawei Islands, west of 

 Smmatra, Pulau Stupai, northern edge of Sanding Islands, in c. — 1-1 m to —5 m, 

 4 XII 63, Hillis- Colin vaux LH 29c. Scale bar is 2 cm. (Photograph by The Ohio 

 State University Department of Photography.) 



