Twigs of sencha are "kikucha".
The twigs of gyokuro are called "karigane".
The dust (not collected on the floor, but on the belt while processing the leaves) is "konacha"
The shoots (that's the small leaves that are too small or the tips of the leaves) are "mecha"
Those products are very common by-products obtained while processing the leaves. Their names are standardised for all Japan and they are sold that way on markets.
On this pages , photos and definitions of konacha / kukicha / mecha
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You can buy in shops blends of twigs and leaves and even matcha. Blends have no standard names, the sellers decides. The Japanese package tends to explain clearly what it contains, or if they are lazy, they only write "ryokucha" (green tea). I think Lewis found leaves in a "kukicha blend".
There exist also (less standard) :
The big stems are "boucha", usually of bancha, and are often roasted. (I never saw them otherwise, but I've not seen everything)
Bancha means leftovers collected later in the season. It's often roasted. It can be aged.
Houjicha can be any *roasted* tea (sencha/bancha/boucha...)., it can be roasted in a number of way. That can be done to recycle leaves of sencha that lose their freshness. I have a sort of pottery with a hollow handle that is a hoji-cha roaster.
There are dozens of regional sorts of bancha/houjicha with as many names. For instance kyobancha is Kyoto-style, the whole leaves are fire-dried/roasted. Other sorts are processed differently. The recipe to prepare them also varies (brewing, simmering...)
Photos of : houjicha/ genmaicha / bancha (not roasted) / kyobancha
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Bancha, bocha, kukicha are said to contain less cafeine. Hojicha is considered cafeine-less. So old people drink them for this reason.
Kuri