21.3: Lycophytes (Class Lycopodiopsida)
- Page ID
- Microphylls. Leaves have a single, unbranched vein of vascular tissue. Note: The term microphyll, confusingly, is not an indication of the size of the leaf.
- Rhizomes. Asexual propogation of the sporophyte through underground stems.
- Homosporous or heterosporous. Haploid spores grow into bisexual gametophytes in Lycopodium. In Selaginella, microspores develop into microgametophytes that produce sperm and megaspores develop into megagametophytes that produce eggs.
Extinct lycophytes like Lepidodendron and Sigillaria grew into tall trees, branching dichotomously and producing a moss-like canopy of microphylls. Some of these microphylls were several feet long! Lycophytes first appear in the fossil record over 400 million years ago. By the Carboniferous period (around 300 mya), the landscape was covered with lycophyte forests and shallow swamps. Much of the fossil fuels we use today are derived from these extinct arboreal lycophytes falling into swamps, slowing decomposition and creating layers of carbon-rich material that we now find as coal seams.
Why would being submerged in water slow decomposition? Consider the cellular process normally associated with decomposition activity and what is required to perform this process.
If available, observe fossil specimens or images of fossils from extinct lycophytes. Do these resemble any plants you see today?
Extant lycophytes (those species still alive today) are represented by creeping forms, such as Lycopodium and Selaginella. Observe fresh specimens and prepared slides of Selaginella and/or Lycopodium. Draw and describe the important characteristics that differentiate these plants from bryophytes, including stem and leaf structure, below ground parts, and where spores are produced.