Bouganvilleas
Begonia
The Dahlia.
Perhaps the question should be "named by a botanist?" Hydrangea - or one of the plants known as the Christmas Flower (also Euphorbia pulcherrima/ Poinsettia) was first named by Carl Linnaeus - the "father" of modern botanical taxonomy.
It means a flower that was named after Anders Dahl, a Swedish botanist.
If you are looking for the answer to a worksheet entitled "5-10 Items Named After People" then the answer is Poinsettia.
Pear
Magnolia is correct. Named after P. Magnol, a French botanist.
Dahlia flowers were not invented. The flower existed for many thousands of years. But many people have hybridized it so there are many thousands of different dahlia.
banksia
Robert Brown, a Scottish botanist
They are named Botanist :)
Joel Roberts Poinsett was Secretary of War for Van Buren. He was also a physician and botanist and held several other government positions. The poinsettia flower is named for him.