The basic unit of biosystematics refers to the fundamental entity that is studied in the field of biosystematics. Biosystematics is a branch of biology that focuses on classifying and understanding the diversity and relationships of organisms. The correct answer is option 2, "Ecotype."

Ecotypes are populations of a species that have distinct genetic and phenotypic characteristics due to adaptation to a specific ecological niche. They may differ in their physical appearance, behavior, and ecological preferences, but they are still considered to be the same species. Ecotypes are important for studying the adaptation of organisms to their environment and the processes that drive evolutionary changes within a species.

Phenotype refers to the observable physical and physiological characteristics of an organism that are influenced by both genetic and environmental factors. Florotype is not a recognized term in the field of biosystematics. Genotype refers to the genetic constitution of an organism.