Senryu: Where Does the Name Come From?
Karai Hachiemon (1718-1790), a government official in the Asakusa area of Edo (now Tokyo), used the pen name of "Senryu" ("river willow"), and the short verse honors his contribution by bearing his name. Karai Senryu was instrumental in popularizing the senryu of his day, and the verses he chose were further screened by Goryoken Arubeshi (the editor's pen name meaning "Please excuse my screening"). These were published as 23 volumes of Haifu Yanagidaru during Hachiemon's lifetime. Though Haifu Yanagidaru continued to be published until volume 167, senryu graudaully declined in quality and came to be called kyoku (crazy verse). Later, Sakai Kuraki (1869-1945) and Inoue Kenkabo (1870-1934) revived senryu as a literary art, and other serious senryu writers have carried on their efforts even today.
source: Yasuhiro Kawamura, First Leaves web site.