The Facts

• The word heterosporous applies to plants which have two types of nonsexual spores (both large and small). These are called megaspores and microspores, according to "Life Cycle of a Heterosporous Pteridophyte" by John Schaffner. The megaspore always gives rise to a female, and the microspore always gives rise to a male. Furthermore, heterosporous plants developed from homosporous plants, and they are considered a great evolutionary leap for vegetation found on our planet.
  
  

Features

• The evolutionary differences between homospory and heterspory plants are vast. In particular, seed plants with female gametes (sex cells) in ovules and male gametes in pollen grains must show differentiation between female and male gametophytes. Furthermore, according to "Heterosporous Plants" at sdsu.edu, heterospory also promotes outcrossing between plants.
  
  

Sporophyte

• Heterosporous plants have an alternation of generations life cycle. This type of life cycle has two phases, the gametophyte and the sporophyte. After attaining a certain size, the sporophyte begins to reproduce by developing cones or flowers at the ends of its branches, according to "Life Cycle of a Heterosporous Pteridophyte" by John Schaffner. The cones have two sets of sporephylls and appear slightly different from ordinary leaves.
  
  

Gametophyte

• The megasporophyll produces the megasporangium. The microsporangium and the megasporangium produce nonsexual spores (microspores and megaspores). Only four megaspores develop and become so large that the megasporangium bulges out. The gametophyte is very small, particularly the male. It produces gametes via mitosis (cell division). The life cycle alternates between the sporophyte phase and the gametophyte phase. This is called the alternations of generations.
  
  

Considerations

• Each generation of the heterosporous life cycle leads to an independent existence of at least a part of the plant's life. The sporophyte is a non-sexual generation. It consists of a leafy shoot and branched roots. The stems do not increase in size; however, they do grow in thickness. The vascular bundles are concentrated within the xylem (specialized tissue used for transporting water to the plant), and they lie in the center of the plant.