Start with the plant part
Before the species, establish whether you are holding leaf, flower, root, bark, seed or fruit. It narrows the field enormously and it determines how to brew whatever it turns out to be. A flat pale slice is a root; a hard curl is bark; a papery flake is probably a husk or a peel.
What appearance settles
Cassia against Ceylon cinnamon is decided by the cross-section: one thick hard curl against many thin layers. Whole chamomile against milled chamomile is decided at a glance. Saffron against safflower is decided by shape — a trumpet-shaped stigma with a pale style, against a flat tongue-shaped floret. These are real tests a reader can apply.
What appearance does not settle
Peppermint and spearmint are distinguishable fresh by stem colour and leaf shape, and largely indistinguishable once dried and cut. Kuding is sold from at least two unrelated genera and they look alike rolled. Rooibos and honeybush are close enough that most people cannot separate them by eye. Where TeaHQ cannot settle something from appearance, its pages say so rather than offering a test that does not work.
The binomial is the real answer
A seller who prints Aloysia citrodora is telling you something; a seller who print 'verbena' is not. Where TeaHQ records a botanical name it is because that name is settled, and where it omits one it is because it is contested. Twenty of the catalogue’s binomials were checked against the USDA GRIN taxonomy in Sprint 18, and the check found three that were wrong.
Smell before you buy, if you can
A material that does not smell of itself in the packet will not taste of itself in the cup, and no brewing technique recovers it. This applies to shade-dried leaf, to lavender, to ground spice and to violet — where the colour survives the supply chain perfectly and the scent does not.