Answer:
Due to difference in size and shape of flower.
Step-by-step explanation:
Two species of plant cannot interbreed with each other because their flowers differ in size and shape. Each flower has different time of maturation and the appearance of reproductive stage as well as difference in their chromosome number. If these factors occurs on the same time and having same number of chromosomes so they are able to interbreed with each other otherwise not so that's why we can say that two species can't interbreed with each other.