Occurrence, Structure and Taxonomic Implications of Fern Constituents

Abstract

The living ferns constitute a large group in the plant kingdom, including as they do about 12,000 species (Pichi Sermolli 1960) (1). They are usually divided into three orders, Ophioglossales, Marattiales and Filicales. The Ophioglossales are sometimes regarded as a distinct class. Both the Ophioglossales and the Marattiales have sporangia which have developed from a group of initial cells (eusporangiate ferns), with the Marattiales being usually regarded as being more primitive than the Filicales whose sporangia originate from a single cell (leptosporangiate ferns). The Osmundaceae are considered to be a primitive member of the Filicales by some authorities and to belong to a separate order by others (2). Indeed, many different systems for classifying the ferns have been proposed, for example, by Christensen 1938 (3); Ching 1940 (4); Copeland) 1947 (5); Holttum 1947 (6); Reimers) 1954 (7); Alston) 1956 (8) and Picni Sermolli) 1958 (9) Even today, pteridologists appear to be of different opinions as regard the grouping of fern taxa, particularly the polypodiaceous ferns, and their phylogenetic relationships. Even the number of the families to be included in the Filicopsida which are recognized by different pteridologists varies from twelve to more than fifty (10). Table 1 shows the relations between the three representative systems of classification of the polypodiaceous ferns (sensu lato) proposed by Copeland (1947), Picm Sermolli (1970) (9b, 11) and Holttum (1947). The tentative classification system which is refered to throughout this review is also shown in Table 1.