Nicotiana sylvestris flowers only during long days and N. tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason for considering N. sylvestris and N. tabacum to be separate species?

Step-by-step solution

The term species evolves from word specific means only those groups of plants or animals come under one species which can interbreed and produce fertile offsprings naturally. N. tabacum and N. sylvestris cannot produce flowers naturally have different photoperiods, hence they cannot belong to the same species. Thus, they cannot interbreed in nature.