Selaginella Spike Mosses Structure and Form

The sporophytes of Selaginella, the larger of the two major genera of living club mosses, are sometimes called spike mosses (Fig. 21.5). The approximately 700 species are widely scattered around the world in wetter areas, but they are especially abundant in the tropics. A few are common weeds in greenhouses. They tend to branch more freely than ground pines, from which they differ in several respects. The two most obvious differences are (1) their leaves each have a tiny extra appendage, or tongue, called a ligule, on the upper surface near the base and (2) they produce two different kinds of spores and gametophytes—an advanced feature referred to as heterospory. The seed-bearing coniferous and flowering plants discussed in chapters to follow are all heterosporous.

Reproduction

Sexual reproduction of spike mosses and ground pines both involve the production of sporangia, but spike moss sporangia develop on either microsporophylls or megasporophylls (Fig. 21.6). Microsporophylls bear microsporangia containing numerous microsporocytes that undergo meiosis, producing tiny microspores. The megasporangia of megasporophylls usually contain a megasporocyte that, after meiosis, becomes four comparatively large megaspores.

Each microspore may become a male gametophyte consisting simply of a somewhat spherical antheridium surrounded by a sterile jacket of cells within the microspore wall. Either 128 or 256 sperm cells with flagella are produced in each antheridium. A megaspore develops into a female gametophyte that is also relatively simple in structure. By the time this gametophyte is mature, however, it consists of many cells that have been produced inside the megaspore. As it increases in size, it eventually ruptures its thickened spore wall and produces

Chapter 21

microphyll sporophyte—

gametophyte sporophyll fertilization archegonium containing egg microphyll sporophyte—

gametophyte fertilization archegonium containing egg

Lycopodium Gametophyte

sporophyll tetrad of spores

Figure 21.4 Life cycle of the ground pine Lycopodium, a homosporous lycopod.

tetrad of spores

Figure 21.4 Life cycle of the ground pine Lycopodium, a homosporous lycopod.

Structure Sporophyll
Figure 21.5 Selaginella, a spike moss.

young sporophyte fertilization microsporocytes undergo meiosis, producing young sporophyte microsporocytes undergo meiosis, producing fertilization

Fertilization Moss

microspore male gametophyte

Figure 21.6 Life cycle of the spike moss Selaginella, a heterosporous lycopod.

microspore male gametophyte

Figure 21.6 Life cycle of the spike moss Selaginella, a heterosporous lycopod.

several archegonia in the exposed seams. The development of both male and female gametophytes often begins before the spores are released from their sporangia. Fertilization and development of new sporophytes are similar to those of ground pines.

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Responses

  • Dawid White
    Where is the gametophyte of selaginella located?
    8 years ago
  • amanda
    Are spike mosses heterosporous?
    8 years ago
  • Sago Proudfoot
    Is a sporophyll or sporophyte bigger?
    8 years ago
  • Anni
    Is a pine branch a sporophyte or gametophyte?
    8 years ago
  • fidenzio
    What is the structure spike in sellaginella?
    3 years ago
  • jessika
    How does spike moss life cycle is?
    3 years ago
  • Negisti
    How selaginella (spike moss) reproduce?
    3 years ago
  • Massimo
    What are the male and female organ of club mosses and spike mosses?
    3 years ago
  • swen
    Why selagenilla is advanced then lycopodium?
    3 years ago
  • Bobbi
    What are the differences between spike mosses and club mosses?
    2 years ago
  • Anneli
    Which one is advance selaginella or lycopodium . and why?
    2 years ago
  • abel
    Why is selaginella more advanced than moss plant?
    2 years ago
  • timothy peckham
    What is the functions of sporangiophores of spike of selaginella?
    1 year ago

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