Astilbe and Spirea

Astilbe noun - Any plant of the genus Astilbe having compound leaves and showy panicles of tiny colorful flowers.

Spirea and astilbe are semantically related. In some cases you can replace term "Spirea" with "Astilbe", this nouns are similar.

Spirea noun - A Japanese shrub that resembles members of the genus Spiraea; widely cultivated in many varieties for its dense panicles of flowers in many colors; often forced by florists for Easter blooming.

Astilbe and spirea are semantically related. You can use "Astilbe" instead a noun "Spirea".