In between Stratiotes and Clethra, which ones was described as a genus in 1753? 
Stratiotes: Stratiotes is a genus of submerged aquatic plant commonly known as water soldiers, described as a genus by Linnaeus in 1753. Clethra: Clethra is a genus of flowering shrubs or small trees described as a genus by Linnaeus in 1753.
Clethra