Convergent evolution is the reason for the presence of 

Succulent stems in euphorbias and cacti are a result of convergent evolution. The North American Cactus and African Euphorbia species originated from two different, but similar plants. These plants were characterised by their slim stems and large, wide leaves. As variations in the climate caused the development of harsh, arid, desert environments, both the cacti and the euphorbias lost their leaves and transferred photosynthesis to their enlarged stems, whose specialized anatomy provides water storage and support. 

Evolution of beaks in Darwin’s finches is an example of adaptive radiation. 

Thorns in Bougainvillea and tendrils in Cucurbita are homologous organs (divergent evolution). 

Hearts in vertebrates are also homologous organs.