Bryophytes and Ferns

Two important groups of nonflowering plants include the bryophytes and the ferns. The bryophytes include the mosses, liverworts, and hornworts. They lack vascular tissues, and therefore do not develop true leaves, stems, and roots. Since bryophytes produce organs that are similar in structure and function to leaves and stems, these organ names are used, however. Being nonvascular plants, bryophytes ordinarily form a low-growing ground cover, never becoming a conspicuous part of the temperate vegetation. While most cells are thin-walled and spherical, elongated cells of conducting tissues develop within the stems of some bryophytes. Leptome and hydrome are analogous to the phloem and xylem tissues of higher plants, respectively. Leaves of bryophytes are produced spirally around the stem. Leaves contain filaments of cells, the photosynthetic lamellae.

Ferns are primitive vascular plants and commonly have complicated arrangements of phloem and xylem tissues within stem and root steles. Most temperate ferns develop elongated underground stems (rhizomes) from which the aboveground leaves (fronds) originate. Developing on the lower side of the rhizome are the slender roots. Fronds, on their inception, are tightly coiled into fiddleheads, termed such because of their resemblance to the carvings on the end of a violin or fiddle. One of the most conspicuous attributes of ferns is the formation of older leaves that are compound, giving them a dissected or lacy appearance. Reproductive structures commonly develop on the underside of fern fronds and are conspicuous due to their brown color in contrast to the leaf's green background. These are the sori in which spores are produced. No development of flowers, fruits, or seeds occurs in the ferns. see also Bark; Bryophytes; Cells; Cells, Specialized Types; Ferns; Flowers; Leaves; Meristems; Roots; Stems; Tissues.

Jan E. Mikesell

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