This review paper emphasizes the importance of biodiversity and biosecurity of natural rubbers. Characteristics of guayule natural rubber and dandelion natural rubber are described by comparison with Hevea natural rubber. Especially, their unique strain-induced crystallization behaviors and mechanical properties are summarized, which suggest that these natural rubbers can be alternative natural rubbers for Hevea natural rubber. The technique of the collection for these natural rubbers is necessary to be developed in order to efficiently get their solid natural rubbers and natural rubber latexes in a high quality.