• The avocado tree produces flowers that cross-pollinate to reproduce.Jupiterimages/Photos.com/Getty Images
  
  The avocado (Persea americana) tree--in the same family as cinnamon, spicebush and bay laurel--produces fruits used in many recipes and most likely originated in southern Mexico, according to the California Rare Fruit Growers website. Seedlings can take as long as eight to 20 years to produce fruit compared to one to two years when grafted. The avocado produces greenish-yellow flowers that have interesting characteristics.
  
  

Sterile Avocado Flowers

• The avocado flower has female and male organs, but they do not function at the same time, according to the University of California. When the flower first opens, it is female, which means the stigma--the portion of the female organ that receives pollen--is operable. The flower only remains open for two to three hours then closes until the following day at which time the flower becomes male, producing pollen.
  
  As a result, approximately 5 percent of avocado flowers that bloom are sterile. This is caused by pronounced dichogamy, which means the male and female organs mature at different times. Sterility occurs because the reproductive organs are not receptive.
  
  

Type "A" Avocado Flowers

• Type "A" avocado flowers are female (Stage I) when they bloom in the morning on the first day. They become male (Stage II) flowers when they bloom in the afternoon on the second day, reports the University of California. Stage I opening exposes the stigma in a receptive mode, which means the flower can accept pollen, become fertilized and produce the avocado fruit. Stage II opens the anthers--the male reproductive parts--and reveals pollen, which can be carried away to fertilize a Type "B" female flower.
  
  Cultivars of this variety include Rincon, Sharpless, Spinks, Gwen and Hass.
  
  

Type "B" Avocado Flowers

• Type "B" avocado flowers bloom as females on the first day in the afternoon. On the following morning, the flower opens with male reproductive organs. Type "B" avocado flowers follow the same reproductive pattern of Type "A." Type "B" flowers cross-pollinate with Type "A" flowers during their synchronized period of receptivity.
  
  Cultivars of the Type "B" group include Arturo, Bacon, Elsie, Linda and Ryan.