Date of this Version
Published in Transactions of the Nebraska Academy of Sciences, Volume 1 (1972).
In most instances the Hydropteridales receive little if any attention in the high school biology class or general botany class at the college level. Information regarding these plants may even be rather sketchy in the college level morphology class and morphology text books. Special emphasis should be used in studying this group because they illustrate the following points. Their general morphology is unique in many respects and their habitat is unusual among the ferns. These plants are very good for illustrating the relation between physiology and morphology. The sporocarps produced in this group are unique among all plants. Because of the above features the Hydroptcridales seem to be a natural group with which to terminate a study of the ferns.
The Hydropteridales, "water ferns", are seldom mentioned in general botany text books, and information is also likely to be meager in the general morphology text. It is recognized that not all plants can receive detailed study in an undergraduate morphology course. For instance, Marchantia and Riccia receive considerable attention in dealing with liverworts but Targionia and Corsinia will likely receive very little attention. With the above statement in mind, it might seem just as logical to ask; why study the Hydropteridales when there are so many other ferns to be treated? It is hoped that the following discussion will show why this often neglected group needs special attention.
The Hydropteridales are a small order consisting of five genera and about ninety species. The taxonomic arrangement of this group is rather artificial. The group can be treated as a single order on the basis of all the members being heterosporus, leptosporangiate, aquatic to semi-aquatic and having sporangia produced in sporocarps. When treated as a single order these ferns are further separated into two families, the Marsileaceae and Salviniaceae. The separation into two families is based on characteristics of the sporocarps, type of vernation, number of nuclei in the neck canal cells, and the number of sperm cells produced in each antheridium. The same characteristics which are used by some morphologists (Campbell, 1918, p. 365; Eames, 1936, p. 197 & 231) for grouping the water ferns into one order and two families are used by others (Sporne, 1966, p. 168 & 171) for grouping into two orders and as many as four families. When divided into two families, the Marsileaceae seem to be a more homogeneous family than the Salviniaceae (Campbell, 1918, p. 396; Scagel, 1966, p. 451 & 454). For the sake of convenience, the water ferns are treated as two families in this article. Tables 1 & 2 contain information regarding the taxonomy, morphology, and distribution of the five genera of Hydropteridales.