Incomplete dominace was first observed in which plant?

Answer: Option A

Incomplete dominance was first observed in the 4' O clock (Mirabilis jalapa) plant. This was first observed by Carl Correns.
Incomplete dominance results from a cross in which each parental contribution is genetically unique and gives rise to progeny whose phenotype is intermediate. Incomplete dominance is also referred to as semi-dominance and partial dominance.