What is conventionally in the category
Chamomile, lemon balm, lavender, valerian and passionflower are the plants most consistently grouped this way in European herbal tradition and in the modern trade. Chamomile is by a wide margin the most drunk of them. The grouping is old and stable across sources, which makes it useful for navigation — a reader looking for an evening infusion will find these on the same shelf almost anywhere.
Where the category comes from
These plants appear together in European herbals going back centuries, and the association carried into commercial blending in the nineteenth and twentieth centuries. Several have parallel groupings elsewhere: chamomile is drunk in the evening across the Mediterranean and Latin America, and lemon balm has a documented history in European monastic gardens. The category is therefore genuinely traditional rather than a marketing invention, whatever its merits.
How they are prepared
Flowers and leaves, steeped rather than simmered: boiling water, five to ten minutes, covered. Valerian is the exception in preparation as well as in flavour — it is a root, so it takes a decoction or a much longer steep, and it smells strongly enough that people meeting it for the first time are usually surprised. Chamomile and lemon balm are mild and forgiving; lavender is potent and easy to overdo, and a small quantity goes a long way.
The limitation, stated plainly
This category is named for what these plants have traditionally been taken for. That is a statement about human practice, not about outcomes. TeaHQ has not yet retrieved or assessed evidence for any of them, holds no position here on whether the tradition is borne out, and will not present the category name as though it settled the question. When the botanical records are built they will carry their evidence tier and their sources on the record itself, and this page will link to them rather than summarise them.