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In some species, they are protected during development by a scale or film of tissue called the indusium (pl.: indusia), which forms an umbrella-like cover. Life cycle significance [ edit ]
Prothallus of the tree fern Dicksonia antarctica (note new moss plants for scale) Spore-bearing plants , like all plants, go through a life-cycle of alternation of generations . The fully grown sporophyte , what is commonly referred to as the fern , produces genetically unique spores in the sori by meiosis .
Sori may be covered by a structure called an indusium. Some ferns have their sporangia scattered along reduced leaf segments or along (or just in from) the margin of the leaf. Lycophytes, in contrast, bear their sporangia on the adaxial surface (the upper side) of leaves or laterally on stems. Leaves that bear sporangia are called sporophylls ...
The indusium is linear and persistent, and the sporangia are brownish. Some common species include Diplazium hymenodes , the peacock fern; Diplazium esculentum , the vegetable fern; Diplazium molokaiense , the Molokai twinsorus fern; and Diplazium lonchophyllum , the lance-leaved glade fern.
For example, fossils assigned to the Dicksoniaceae, a member of the Cyatheales, are known from the Lower Jurassic 19] A number of other extinct families have been described. They are not included in the classification systems used for extant ferns, and so most cannot be assigned to orders used in these systems.
Athyrium (lady-fern) is a genus of about 180 species of terrestrial ferns, with a cosmopolitan distribution. It is placed in the family Athyriaceae , in the order Polypodiales . [ 1 ] [ 2 ] Its genus name is from Greek a- ('without') and Latinized Greek thyreos ('shield'), describing its inconspicuous indusium (sorus' covering). [ 3 ]
The genus differs from the well-known and allied fern genus Dryopteris in the indusium being circular, not reniform, and in having the leaf segments with auricles—asymmetrical blades where one side of the segment is much longer than the other at the base.
Generally, the family is pantropical, but due to the distribution of Pteridium (the most widespread fern genus), Dennstaedtiaceae can be found worldwide. [4] Pteridium is a well adapted early successional genus, generally described as a weed because of its ease of spread.