GLOEOTRICHIA J. G. Agardh 1842, p. 8 

 A free-floating or attached hemispherical or globose colony of 

 radiating trichomes, tapering from basal heterocysts and much 

 attenuated at the apices; colonial mucilage soft or rather firm 

 according to species (but not rubbery and not so tough as in the 

 genus Rivularia), either colorless or becoming ochraceous with age 

 in some species; sheath of the trichome usually confluent but often 

 evident in the basal part of the trichome; heterocysts solitary ( rarely 

 2), basal as well as intercalary, globose to oval; vegetative cells 

 short in the basal portion of the trichome but becoming barrel- 

 shaped, longer and cylindrical distally; gonidia cylindrical, usually 

 single, adjoining the heterocyst, rarely in a short series, the mem- 

 brane thick and smooth. 



Species of Gloeotrichia are included with Rivularia by some 

 authors. Separation is here arbitrarily made on the presence of the 

 gonidia, Rivularia lacking them. The latter genus includes species 

 which are always attached and which have very firm, sometimes 

 hard mucilage, often encrusted with lime. The hemispherical col- 

 onies of both genera are macroscopic in size and similar in general 

 appearance. In Rivularia the colony may be hollow, and the radiat- 

 ing filaments are in concentric zones as a result of false branching. 

 In some species of Rivularia agglutinated and expanded gelatinous 

 attached masses are formed. In Gloeotrichia the colonial mucilage 

 is softer and the trichomes definitely radiate and not zoned. Branch- 

 ing is less common. Whereas some Gloeotrichia may remain attached, 

 most species become planktonic or free-floating, especially G. 

 echinulata and G. natans. 



Key to the Species 



1. Colonies globular, planktonic -__-- G. echinulata 



1. Colonies not planktonic or, if free-floating, not globular and burr-like 2 



2. Colonies containing only a few trichomes; cells very long and 

 cylindrical, rounded at the ends; a conspicuous granule at each 



cross wall .'. ___ G. longiarticulata 



2. Colonies containing numerous trichomes; cells quadrate or 

 slightly longer than wide, or shorter than wide in the basal 



portion; end walls not rounded or marked by conspicuous granules - 3 



3. Colonies globular or hemispherical, 1-5 mm. in diameter; attached, 

 sometimes completely coating aquatic plants G. Pisum 



3. Colonies irregularly globose or bullate, 5 mm. to 10 cm. across, 



becoming soft and irregularly expanded and floating when old — G. natans 



Gloeotrichia echinulata (J. E. Smith) P. Richter 1894, p. 31 



PI. 134, Figs. 1, 2 

 A free-floating, spherical, gelatinous colony of many sheathed 



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