Answer: Plasmodium falciparum
The key identifying features are:
1. The infected RBCs are not enlarged (compared to the enlarged RBCs infected by P. ovale and P. vivax.
2. Parasite rings are small and delicate, occupying approximately 1/3 of RBC diameter.
3. Applique or Accole forms are present. These are rings that appear to be 'stuck' onto the edge of the RBC.
4. Presence of Maurer's clefts or dots. These are cytoplasmic structures derived from the malaria parasite. They have a similar appearance to the 'stippling' seen in infection with P. ovale and P. vivax, but the dots are fewer and larger. In order to see Maurer's clefts, it is essential to have your malaria buffer at the proper pH, that is, at 7.2.
Maurer's clefts and stippling are not seen in infection with P. malariae.