366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 196 2 



phyta, and the red Ehodophyta. Among marine green algae, calcified 

 forms occur only in a few families, largely confined to warm seas. 

 Indeed, relatively few genera and species of green algae are calcareous. 

 Nonetheless, in their tropical habitats these plants are often re- 

 markably abundant, and sometimes are among the most conspicuous 

 members of the local marine community. Thus, on some of the gently 

 shelving, intertidal flats of Okinawa, one wades ankle deep in a 

 veritable meadow of Acetabularia — acre upon acre of almost pure 

 stands of these remarkably beautiful little green parasols. In the 

 sandy bays of Cuba, the Bahamas, and south Florida, one finds an 

 abundance of the strange Neptune's shaving brush (PeniciUus), the 

 little Christmas-tree-like Rhipocephalus, and the delicate green, fan- 

 like Udotea. Among the coral heads and rubble flats on the bottoms 

 of the vast atoll lagoons of Kwajalein or Eniwetok, mounds and mats 

 of Flalimeda grow in such persistent plenty that the lagoon floor sedi- 

 ments are largely built up of the accumulated fragments of these 

 jointed plants. 



Then there are the strangely and intricately fashioned species of the 

 family Dasycladaceae : Dasydadus^ Bometella, and Neomeris. These 

 are tiny little plants, often inconspicuous, but sometimes the most 

 striking members of an undersea flora. I remember diving one day in 

 a warm island lagoon in the Gulf of California and being impressed 

 by great, round boulders on the bottom that were studded with little 

 glistening, upended "worms" of a brilliant emerald color— the green 

 alga Neomeris. Many members of this family are known from the 

 fossil record and have contributed to the formation of limestone rocks. 



Among the brown algae, calcareous species are few, confined largely 

 to the tropical genus Padina., whose interesting, fan-shaped represent- 

 atives may be found in almost all warm seas. Padina commonly has 

 concentric bands of superficial calcium carbonate alternating with 

 bands of delicate yellow-brown hairs and underwater sometimes 

 stands out as the most gracefully formed and artfully patterned plant 

 of the sea floor. 



In red algae, as in the other two groups, the occurrence of calcified 

 forms is limited to a few families. One of these, however— the Coral- 

 linaceae— is of wide distribution. The only other important cal- 

 careous genera of red algae are Gcdaxaura, Liagora, and Peysonnelia. 

 These occur mostly in the tropics, but are seldom abundant or 

 conspicuous. 



Thus, the Corallinaceae includes the overwhelming majority of the 

 calcareous plants of the world. They occur from the Arctic to the 

 Antarctic and from the highest and most inhospitable intertidal levels 

 to the cold, dim depths of ocean at the extreme limit of light penetra- 

 tion. Sometimes a score of species may live in a single habitat. Again, 



