Answer: Plasmodium falciparum
Shown here are early trophozoites (rings) of P. falciparum with Maurer's clefts. Although some of the infected red blood cells (RBCs) have a ragged edge that may be mistaken for the fimbriations of P. ovale infected cells, the size of the RBCs is normal compared to the surrounding cells, the cytoplasmic dots (called Maurer's clefts) are few and large (compared to the numerous small stipples in P. ovale/P. vivax), and the trophozoite forms are delicate. These three features support the diagnosis of P. falciparum rather than P. ovale. I've highlighted some of these features in the images below.
Below is a dual image showing P. falciparum and P. ovale infected RBCs side-by-side. Note how the Maurer's clefts of P. falciparum are larger and fewer in number than the multiple small cytoplasmic dots (Schuffner's dots) of P. ovale. Also note the larger size of the infected RBC in P. ovale infection and the thicker ring form.
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