HIGHER LAND PLANTS 



181 



Figure 11.16 Marattia, a tropical fern. (Used by permission, from 

 Crypfogomic Botany, vol. 2, by Gilbert M. Smith. Copyright 1955. 

 N. Y.: McGraw-Hill Book Co.) 



ORDER FIUCALES (True Ferns) 



Diagnosis: known from Pennsylvanian to Recent; 

 variable occurrence and growth habit; United States 

 species are perennial herbs, mostly fern-like but rang- 

 ing from creeping to climbing plants of moss-like to 

 tree-like form; stems commonly underground and 

 branched; leaves unroll with growth and are variable, 

 mostly large but either simple, compound, or decom- 

 pound and often pinnatified; sporangia mostly upon 

 margin or under surface of leaves, occurring singly 

 or in groups (sori); sori with or without a protective 

 covering (indusium); one spore type; gametophyte 

 usually bisexual, generally inconspicuous ('/jg to ^2 

 inch), above ground, membranous, and chlorophyl- 

 lous (Figure 11.17). 



Occurrence: about 10,000 species forming several 

 families of world-wide distribution; perennial herbs to 

 trees, rarely annuals, mostly of moist climates and/or 

 moist habitats, some in dry areas. 



ORDER MARSILEALES (Wafer Ferns) 



Diagnosis: fossil record obscure; aquatic or semi- 

 aquatic forms that are not at all fern-like; primarily a 

 creeping rhizome bearing filamentous or clover-like 

 leaves; sporangia in modified nut-like structures (spo- 

 rocarps) at or near the base of the leaf petioles; two 

 spore types, producing much-reduced male and fe- 

 male gametophytes that approach those of seed plants 

 (Figure 11.18). 



Occurrence: three genera of perennial herbs in a 

 single family, Marsileaceae; one species of Regnil- 

 lidium, a South American form characterized by bi- 

 lobed, simple leaves; six species of Piluldna in northern 

 Africa, Europe, Australia, and America (one Amer- 

 ican species, P. amencana, the pillwort) characterized 



Figure 11.17 Pteridium, a true fern. {Used by permission, from 

 Cryptogamic Botany, vol. 2, by Gilbert M. Smith. Copyright 1955. 

 N. Y.: McGraw-Hill Book Co.) 



