Category: 03. Ferns

The leaf (also known as frond) of ferns is the part of the plant most readily visible to observation. The leaf plan in practically all ferns is pinnate—that is, featherlike with a central axis and smaller side branches—and this is considered to be the primitive condition because of its widespread occurrence. From this basic type a broad diversity of forms evolved. Some ferns have…

Fern roots are generally thin and wiry, although some are fleshy and either slender (in the Ophioglossaceae) or as much as 13 mm (0.5 inch) in diameter (e.g., Acrostichum and Marattia). The relation of the roots to the stems is a valuable identification tool. For example, in certain tree ferns (e.g., Cyathea and Cibotium) and in the royal ferns (Osmunda), the entire stem surface is covered…

The steles—cylinders of vascular tissues in the centres of fern stems—exhibit somewhat diverse patterns. Most common ferns possess a “dictyostele,” consisting of vascular strands interconnected in such a manner that, in any given cross section of stem, several distinct bundles can be observed. These are separated by regions filled with parenchyma cells known as leaf gaps. There are, however, numerous “siphonostelic” ferns,…

The cortex is the region outside the vascular cylinder but below the surface of the stem. It is composed mostly of storage parenchyma cells (a relatively generalized cell type). Rooting animals, such as pigs, occasionally dig up fern rhizomes for the starchy materials contained in them. There is a strong tendency for the outermost cortical cells to become darkly pigmented…

Whether covered with leaf armour or not, the surface of the fern stem is protected by an epidermis, or “skin,” a single layer of epidermal cells, which are more or less flat cells with thick outer walls. Most fern stems also are covered with a protective indument, consisting of hairs, known as trichomes, or scales; these are…

Fern stems vary from the tall, narrow trunks of certain tree ferns that reach 25 metres (80 feet) tall down to clumped or creeping rootstocks, or rhizomes. Rhizomes are the most common stem form. The majority of them grow horizontally upon or just beneath the surface of the soil. Some stems are so narrow as to be threadlike,…

Within the archegonial venter the zygote undergoes characteristic cell divisions to form the embryo, which remains encapsulated in the gametophyte until it breaks out and becomes an independent plant. The pattern of development in most ferns is a distinctive one, and indeed only in the Botrychium subgenus Sceptridium and in all species of the family Marattiaceae thus far studied are found conditions of embryonic development resembling those of seed plants. Here…

The sex organs of ferns are of two types. The sperm-producing organ, the antheridium, consists of a jacket of sterile cells with sperm-producing cells inside. Antheridia may be sunken (as in the families Ophioglossaceae and Marattiaceae) or protruding. They vary in size from those with hundreds of sperm to those with only 12 or so. The egg-producing organ, the archegonium, contains one gamete (sex…

Vegetative propagation of some photosynthetic fern gametophytes is accomplished by continued growth and fragmentation, but this does not spread the gametophyte very far. Some ferns (Vittaria, Grammitis, and the family Hymenophyllaceae) produce specialized filaments, or gemmae, that break off and are carried away by water droplets, wind, or possibly insects or spiders to initiate new colonies.

From a basic type of gametophyte, somewhat like that just described, a number of highly specialized forms have evolved that are characteristic of certain genera. Ribbonlike and strap-shaped gametophytes are known especially among tropical rainforest ferns such as Vittaria, Grammitis, and Hymenophyllum and are usually irregularly and extensively branched, forming large masses of intertwining ribbons. Some of these are actually more abundant than…