Stidd, Benton M. Department of Biological Science, Western Illinois University, Macomb, Illinois.
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An order (class Polypodiopsida) of primitive ferns that consists of about seven living genera and 150 species. They exist mostly in tropical regions. These large, coarse, sappy ferns usually have large, highly divided fronds. Danaea simplicafolia, however, has an undivided frond consisting of a single blade. Stems of living genera (Angiopteris, illus. a; Marattia) are short and bulbous, often a foot or more in diameter. Other genera have smaller, mostly horizontal, and somewhat more elongated stems. The internal vascular system (food and water conduction tissue) of the stems and fronds can be quite complex, apparently as a function of size. Marattialeans are included among the primitive ferns primarily because of the way that the sporangia (spore-bearing organs) arise from a mass of cells rather than from a single cell as in more highly evolved ferns. Sporangia are generally fused together into a synangium. Synangia are borne on the lower surface of the pinnules and are usually elongate. Christensenia differs from other genera in having palmately branched fronds (pinnate in other genera), net venation, and circular rather than linear synangia. Gametophytes (the small plant generation bearing egg- and sperm-producing organs) are large (among ferns) and thick and resemble thallose liverworts.
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