A GUIDE AND KEY TO AQUATIC PLANTS 3 



compound or simple, dissected, lobed, or otherwise, is of only slightly less 

 importance. The manner of attachment, whether alternate, opposite, 

 or whorled, is a commonly used point of separation, as is the character 

 of the leaf margin, whether hairy, toothed, etc. Other characters also 

 much used are the nature of the apex of the leaf, the manner of vena- 

 tion, and such sensory characters as color, odor, and feel. Relative 

 size is, as stated before, often used. Leaves are used in the majority 

 of the key separations, and it is of primary importance that the leaf 

 terminology be learned. 



Flowers are more diverse than other plant structures, and the lay- 

 man is often dismayed by the complex terminology. Only the 

 absolutely necessary terms are used in the keys of this guide. Typ- 

 ically a flower consists of a stalk {pedicel or peduncle) upon the summit 

 of which are borne several concentric whorls or cycles of floral parts. 

 The outermost whorl is the calyx, made up of the ordinarily green 

 sepals. Next outermost is the corolla, made up of petals which usually 

 give color to the plant. Unfortunately petals are often lacking, and 

 if only one whorl of accessory flower parts is present, they are termed 

 sepals, even though sometimes colored. Within the petals is one or 

 more whorls of pollen-bearing stamens, and within these is the inner- 

 most whorl consisting of one or more pistils which ultimately give rise 

 to the seed. Sometimes stamens and pistils are found only in separate 

 flowers, but usually they occur together. The stamens and pistils are 

 usually termed the essential flower parts in contrast to the accessory 

 sepals and petals. Flowers are borne either alone or in clusters known 

 as inflorescences. Several types of inflorescences are illustrated in the 

 glossary, small circles representing individual flowers, and lines the 

 stalks. 



In using the key several floral characters are used, color and size 

 being of much importance. The shape and number of parts is also 

 important as is the type of inflorescence. Also used is the extent of 

 union of parts as sepals and petals are often partially or wholly united. 



Two families of plants merit special attention as regards terminology. 

 These are the grasses, Gramineae, and the sedges, Cyperaceae. Both 

 are important and difficult aquatic groups. Below (figures 1 and 2) 

 are diagrams of the morphology of the two families. In recognizing 

 grasses the ligule of the leaf is of great importance. This structure, 

 present at the inner base of the leaf where it joins the leaf-sheath, varies 

 in size and nature but may usually be detected. The arrangement of 

 grass leaves in two ranks or rows up and down the stem is also of great 

 importance. Sedges may be distinguished by the absence of a ligule 

 and the three-ranked arrangement of the leaves. 



The arrangement of the flowers in the two groups is similar in some 

 respects and different in others. Both have the small flowers or 

 florets grouped one to many in spikelets. In the grasses each spikelet 



