It means a life cycle where a plant has a period in life when it can reproduce sexually and another time when it can reproduce asexually.

What plants have seeds located in a cone? 

Where can the pollen grains of conifers be found? 

 What is the main pollinating agent of conifer plants?

 Fern plants have two stages in their life. One is the sporophyte stage. What is the other stage?

What is the shape of a gametophyte fern plant? 

 When the sporophyte matures, what type of reproduction can occur?

In what stage does the moss plant can either be male or female? 

What is the main pollinating agent of moss plants? 

What other means of asexual reproduction can mosses undergo to spread and multiply?