Common yarrow

Name: Common yarrow 

Scientific name: Achillea millefolium

Family: Asteraceae
Possible uses: colds, fevers, digestive problems, internal bleeding, first aid for wounds and nosebleeds, preventing/clearing blood clots, moves stagnant blood, menstrual problems, induce sweating, migraine, thrombosis, hemorrhoids, vaginal discharge, hypertension, coronary thrombosis, diarrhea, dysentery, arthritis, rheumatism, toothache, earache, colic, cystitis

Part of plant used: leaves

Possible side effects: external use may cause dermatitis, avoid internal use

Description: Perennials with aromatic foliage, often finely divided.  About 80 species, native to the north temperature zone.  A traditional European herb that grows as a wildflower throughout the USA, with flat clusters of small white flowers and pungent, gray-green, fern-like leaves.  Flower stalks can reach 2-3 ft. tall; a patch can spread 2-3 ft. wide.  The foliage is evergreen in mild climates, nearly so in cold climates.  A natural for meadow gardens, it also tolerates mowing and light traffic and spreads to make a surprisingly versatile ground cover.  Perennial nurseries offer several new cultivars and hybrids with flowers in a wide range of bright and pastel colors.  Zone 3.
Habitat: Roadsides, meadows, lawns
How to grow: Full or part sun.  Ordinary soil and watering.  Cut flowers as they fade to prolong blooming.  Easily propagated by seed or division.  Pest-free, but leaves may rot in hot, humid weather.
Contraindications: children under 5 years, pregnant, breastfeeding

Said to be able to stop or start a nosebleed.  It can also stimulate uterine contractions, so it's best to avoid in pregnant patients. 

Sources
Refer back to the Sources 

Taylor's Guide to Herbs
Backyard Medicine by Julie Bruton-Seal and Matthew Seal