**Core Concept**
The diagnosis of malaria requires the identification of the parasite stage and morphology on a malarial slide examination. This case presents with all stages of parasites, including schizonts with a specific size and number of merozoites, and a yellow-brown pigment.

**Why the Correct Answer is Right**
The description provided matches Plasmodium vivax, a species of malaria parasite characterized by the presence of all stages of parasites, including schizonts with 14-20 merozoites per cell. The yellow-brown pigment is likely hemozoin, a byproduct of hemoglobin degradation by the parasite. The size of the schizonts (20 microns) also supports the diagnosis of P. vivax. The presence of all stages of parasites suggests a relapse or a chronic infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the description provided.
**Option B:** This option is incorrect because P. falciparum typically presents with a smaller number of merozoites per schizont (usually 6-8).
**Option C:** This option is incorrect because P. ovale also presents with a smaller number of merozoites per schizont (usually 8-12).

**Clinical Pearl / High-Yield Fact**
It's essential to note that the size of the schizonts and the number of merozoites per cell can help differentiate between Plasmodium species. A high index of suspicion and a thorough examination of the malarial slide are crucial for accurate diagnosis.

**Correct Answer: D. Plasmodium vivax**