Mellow Monk's green tea is a type of sencha known as tamaryokucha (玉緑茶), which literally means "curly green tea." Tamaryokucha is grown and harvested the same way as straight-leaf sencha, and it's processed the same way, except for the very end of the teamaking process, where the leaves are rolled to make them curly.
Tamaryokucha, which is appreciated for its less-astringent flavor compared to Tokyo-style straight-leaf sencha, is made primarily on the island of Kyushu, where Mellow Monk tea also comes from.
I've seen some discussions on the 'Net asking whether tamaryokucha is the same thing as "guricha." The answer—doubled-checked and verified by our growers—is a most definite "yes": the two terms refer to the same tea.
The name "guricha" also means "curly tea," with "guri" being the name of a curly design pattern seen in traditional Japanese architecture and crafts (see the bottom photo below).
A close-up of the curly leaves of Monk's Choice Green Tea, a typical tamaryokucha (or "guricha").
A guri design carved into a wooden box.