Another line of terrestrial plants (distinct from the bryophyte line) evolved that developed specialized cells and tissues in the sporophyte generation. For this group the sporophyte became the dominant stage in terms of size and is the principal life stage for photosynthesis. These plants evolved into a considerable diversity of forms and are sometimes known as the primitive or lower vascular plants ("vascular" because of their xylem and phloem). Review xylem and phloem from your Biology 230 course. While complex and specialized tissues represent a significant evolutionary development, these groups still maintain many primitive life cycle features that are holdovers from their common ancestry with the algae.

(A) Feature of extant club mosses and horsetails relating to success on land:

• Derived Features Relative to Bryopsids
  • 1. Incorporation of photosynthesis and spore dispersal in one thallus. The sporophyte is a successful combination of functions. Both have some of the same environmental needs (sun, air, sturdy erect plant).
  • 2. The sporophyte is adapted to life on land: it has a cuticle, lignin, vascular tissue, and stomata.
  • 3. Vigorous rhizome growth produces new shoots. This quickly renews the sporophyte generation and maintains the population in an area. It bypasses the slow cycling through the gametophytic generation.
• Ancestral Features Relative to Bryopsids
  • 1. Leaf small with one vein, limiting efficiency of translocation and growth.
  • 2. Water is still required for fertilization.
  • 3.Alternation of two independent generations (gametophyte and sporophyte) having different growth needs and somewhat different habitats.
  • 4. Gametophyte restricted to moist places - lacks cuticle, lignin, and vascular tissue.
  • 5. Gametophyte generation slow growing, requiring months to years to produce zygote.
  • 6. Spore is slow to germinate.