THE MARINE FLOWERING PLANTS 



LTHOUGH the vast majority of seashore plants are algae, 

 there are many localities along both the Atlantic and the 

 Pacific coasts of the United States at which one will find 

 at least one kind of flowering plant growing under strictly 

 marine conditions in intertidal water or below. Some- 

 times these "sea grasses" may be so abundant as to form 



great beds on sand, mud or rocks to the virtual exclusion of other 



kinds of plants. 



Inasmuch as there are only a tew kinds of these "sea grasses" a 

 key to them is unnecessary, and they may readily be identified by the 

 use of the illustrations and notes which follow. Each of the common 

 genera is illustrated. Only Halophila is omitted, for it may be en- 

 countered in quantity only in the Florida keys. Its species have small 

 elliptical, petiolate leaves. 



Fig. 240. Zosfera marina Linnaeus (Eel Grass) A, B, C, X 0.5; D, X 1. 



This is our most common and widespread marine flowering plant. 

 It occurs along the Atlantic Coast from southern North Carolina north- 

 ward, and, in favorable locahties, along the entire Pacific Coast of the 

 United States. It commonly lives on tidal mud flats and in bays and 

 estuaries from low tide level down to twenty feet or more. The illus- 

 trations marked "A, B, C" show three variants of this species of which 

 the narrow-leaf forms "A, B" are like those found along the Atlantic 

 Coast and in some sheltered bays and estuaries along the Pacific. The 

 large, broad-leaf form shown in "C" is known as Zostera marina var. 

 latifolia Morong, and is the commoner form of Pacific shores. Along 

 the open southern California coast it is often found on sandy bottoms 

 in depths of fifteen feet or more. Fragments of the plants are com- 

 monly cast up on sandy beaches. 



The flowers and fruits of eelgrass are rather obscure. Part of a 

 fertile stem (spadix) is shown at "D," and two developing seeds are 

 visible where the enveloping spathe does not completely cover them. 



Because eelgrass is an important food plant of birds and of many 

 marine animals along our coasts, it received a great deal of attention 

 about twenty years ago following its almost complete disappearance 

 from the Atlantic Coast in 1931-32. The importance of this destructive 

 "wasting disease" of Zostera led to much scientific research in an at- 

 tempt to determine its cause, and although not proved, the most likely 

 cause is now thought to have been a parasitic mycetozoan, Labyrinthula, 

 living within its leaves. It took about fifteen years for the eelgrass to 

 return to normal growth, apparently through the development of strains 

 more resistant to the parasite. 



180 



