The Koshu Sect (洪州宗)
The Koshu sect (Hongzhou-zong) was a sect of the Zen sect (Chan-zong) in the Tang Dynasty. In the history of the Zen sect, among the branch sects of Nanshu-zen (Nanzong-chan) from the sixth leader Eno (Huineng), the sect, founded by Baso Doitsu (Mazu Daoyi) who was a successor of Nangaku Ejo (Nanyue Huanrang), has been called the Koshu sect after the sect's base Jiangxi-sheng. Izan Reiyu (Weishan Lingyou) and Rinzai Gigen (Linji Yixuan) had studied at the Koshu sect. The Igyo sect (Weiyang-zong) and the Rinzai sect (Linji-zong), which they had founded, developed as ones of the five houses and seven sects of Chinese Zen.
The Koshu sect originated from Baso Doitsu, and Hyakujo Ekai (Baizhang Fuanhai) established the disciplines of the Zen temple with 'the Regulations by Baizhang' and formed an original system of the religious community of the Zen sect. As Izan Reiyu and Obaku Kiun (Huangbo Xiyun) of the Obaku Sect (Huangbo-zong) were students of Hyakujo and Rinzai Gigen was a student of Obaku Kiun, their thoughts were handed down to the Igyo sect and the Rinzai sect.