Herb
Purging and purple — the cleansing herb of the psalm, whatever the psalm meant.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Hyssop's standing in Western practice rests almost entirely on one line of the fifty-first psalm, in which the speaker asks to be purged with hyssop and made clean. It is quoted at cleansing rites, written on jars of floor wash, and cited as scriptural warrant for a whole genre of purification work.
The complication is that nobody is sure the biblical plant is this one. Hyssopus officinalis is a Mediterranean shrub of the mint family with deep blue-purple flower spikes; the Hebrew ezov has been identified variously with Syrian oregano, a caper, and several other candidates, and the Greek translators' choice is the reason we call this plant hyssop at all. The correspondence is real and inherited; the identification behind it is shaky.
Practice uses it for cleansing above all — bath and floor washes, asperging, clearing a house before moving in. Bees love it, it makes a low hedge, and it is one of the more forgiving Mediterranean herbs to grow in a cold garden.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper assigns hyssop to Jupiter under Cancer, and recommends it for the chest and lungs in the confident manner he brings to everything. He does not touch the question of whether it is the plant the psalm meant.
Carried forward
Duskveil editorial note
The cleansing correspondence comes from scripture by way of a Greek translation, and the plant the Hebrew names may not be this one at all. That does not make the inherited use invalid — it does mean the pedigree is shorter than it looks.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.