Stolen shamelessly from Artesia: Adventures in the Known World...

Althaea (marsh mallow): Root pulverized into a poultice that heals wounds.
Angelica: Leaves brewed into a potion that wards off disease and magic, and cures disease.
Blueweed: Leaves powdered and sprinkled on something to ritually purify it.
Borage (starflower): Flowers brewed into a potion that provides courage.
Calendula (marigold): Flowers brewed into a potion that helps divine someone's future lover.
Cowslip: Flowers brewed into a potion that cures paralysis and restores strength.
Goldenrod: Leaves mashed into a poultice to stop bleeding and cure poison.
Henbane: Leaves dried and hung by an outer door to ward the building and those within against magic.
Horsetail: Leaves powdered and sprinkled on something to ritually purify it.
Hypericum: Leaves and flowers crushed and powdered, sprinkled on a place or person to help with exorcisms and summonings.
Juniper: Berries brewed into a potion to protect from fevers, hexes, curses, the Evil Eye, and to reduce fevers or counter hexes and curses.
Levisticum (lovage): Leaves brewed into a "love" (lust) potion.
Mallow: Shoots brewed into an anti-love/lust potion.
Mandrake: Root (preferrably from below a hanging-site) brewed into a potion of fertility.
Monkshood (aconite, wolfsbane): Juice smeared on a weapon as a poison.
Mushrooms: Brewed into a potion that permits spirit-walking / astral travel.
Myrtle: Leaves brewed into a love potion.
Pennyroyal: Leaves brewed into an abortificant.
Rue: Leaves brewed into a potion that grants second sight (ability to see spirits or magic).
Sealwort: Roots prepared as a poultice to heal incapacitated limbs.
Scorpion: Body powdered and brewed into a potion to ward against poison and cure poison.
Wormwood: Branch hung by a door to ward off spirits and elementals. Leaves & oil juiced and brewed into a potion to protect against magic.
Yarow: Leaves prepared in a poultice to heal wounds over several days. Leaves powdered and brewed into a potion to help with reading the future.

In game terms, these could translate to bonuses to related tests, or require a skill check to work (in A:AKW, the effects require an enchantment and the effects vary by skill and power expended).