HOW TO KNOW THE SEAWEEDS 



163a Thallus branched in the manner of an Opuntia cactus, the blades 

 or branches all more or less circular or elliptical in outline. Fig. 

 207 Opuntiella calUomica 



Figure 207 



Fig. 207. Opuntiella californica (Fallow) Kylin . 



Habit of an entire plant, X 0.28. Grows on rocks at lowest tide 

 levels and below from central California northward, but usually as 

 isolated thalli. It is more frequently found in beach drift. It should be 

 pointed out that juvenile or poorly developed plants of this species will 

 be difficult to recognize, for the distinctive cactoid form will not neces- 

 sarily be evident. 



163b Not as above; blades or branches not at all circular in shape. . 164 



164a Primary branching of thallus dichotomous or subdichotomous, or 

 subpalmate to produce a flabellate form at least in upper parts. 165 



164b Primary branching essentially in one plane, but not dichotomous, 

 subdichotomous or subpalmate. (But note dichotomous tendency 

 in Fig. 224) 178 



157 



