Variation in the Number of Ribs in Gostaria costata 



Catharine W. Smith 

 University of Washington, Seattle. 



Postels and Ruprecht (1840) describe the genus Costaria as "5-3 cos- 

 t;vta/' and give a jolate showing a 5-ribbed specimen. J. Agardh (1848) 

 agrees with this. IMost of the literature on the genus succeeding these rec- 

 ords no other variation in the number of ribs. Whether 3-5 (the figures 

 are given 5-3) mean that there are fronds with 3, 4 and 5 ribs respectively, 

 or with 3 and 5 ribs only, is not distinctly specified. Some descriptions state 

 that "the ribs . . . are five in number" (Setchell 1893), and mention 

 no variation at all. Setchell (1911) says the blade has "several (4-5) 

 longitudinal ribs." This is the only specific reference found to a 4-ribbed 

 Costaria, and 3 ribs are not included. Muenscher (1917) describes Cos- 

 taria as having "5, or rarely 3, longitudinal ribs." The species referred to 

 in every case mentioned is Costaria costata (Turn.) Saunders [^Costaria 

 turneri (P. & R.)] 



During the summer of 1919 in the waters in the vicinity of the Puget 

 Sound Biological Station, many fronds of C. costata were gathered 

 which show great variation in the number of ribs. All specimens were 

 gathered and preserved for the Director of the Station by Miss Leona 

 Sundquist of the University of Washington, and handed over to the writer 

 to report upon. Most of them were secured off the shores of Blakeley 

 and Turn Islands, perhaps because these localities were visited most often. 

 The frequency of finding these variants indicates that they are not ex- 

 tremely uncommon. No account of C. costata with more than 5 ribs seems 

 to have been published , nor any variation in the inimber of ribs within 

 the length of a single blade. For these reasons it is thought that perhaps 

 the observations on the unusual features recorded in this pajjer may be 

 of interest. 



It has been established that the growing point of Costaria is 

 near the base of the blade (Fallis 1916). Small plants are generally the 

 only ones which have all their parts, since the early growth of larger 

 fronds is invariably worn away . In all cases here discussed the tips of 

 the fronds are missing, and in one instance the holdfast end is also torn 

 away. 



No 3-ribbed fronds were found. The number or ribs ranged from 

 4 to 9. Not all the ribs necessarily extend the whole length of the 

 frond. In fact, of the fronds which are not typically 5-ribbed, there are 



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