Pollen as large as about 90–100 µm. In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of sporogenous cells form within the anther. The fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. In a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell
Heliconius charithonia and show superior mimetic diversity to those that do not. Adult butterflies choose their home ranges based on collections of pollen plants. An adult collects pollen by inserting its proboscis into the flower while making particular movements to secure adhesion to the pollen grains. Digestion occurs immediately after ingestion when the pollen makes contact with saliva, and amino acids are dissolved. Optimal amino acid intake occurs through abundant saliva production and gentle and slow mastication. During the night, the butterflies digest pollen since optimal nutritional resources are obtained while resting or sleeping. Pollen feeding is correlated with higher overall fitness.