Family - Asteraceae

Stems - To +70cm tall, from rhizomes, herbaceous, lanate, branching in upper half, erect, fragrant when crushed.

Stem close-up.

Leaves - Alternate, sessile, linear to lanceolate or oblong, twice or ternately pinnatifid, lanate below, sparse lanate above. Basal leaves to +25cm long. Cauline leaves typically to +10cm long, +3cm broad.

Basal leaf.

Inflorescence - Flat or domed terminal cymose arrangement of flower heads.

Involucre - 5mm tall(long), 3mm in diameter. Phyllaries in 2-3 series, with scarious margins, lanate pubescent, imbricate. Outer phyllaries shorter than inner.

Involucre(s) close-up.

Ray flowers - Ligules typically 5 per flower head, white to pinkish, 5mm long, clawed. Expanded portion of ligule 3mm long, 2-3mm broad, emarginate or shallow 3-toothed at apex. Claw 2mm long, greenish, glandular. Achene flattened. Pappus none.

Disk flowers - Disk to 3mm in diameter. Flowers typically 5-20 per flower head, fertile. Corolla tube to -2mm long, greenish, 5-lobed. Lobes white. Achenes flattened. Pappus none. Receptacle slightly convex, with chaff equaling disk flowers.

Flowers close-up.

Flowering - May - November.

Habitat - Roadsides, railroads, disturbed sites, pastures, fields, prairies.

Origin - Native to the U.S. and Europe.

Other info. - The plant has a strong odor when bruised or crushed.
According to Steyermark there is another subspecies in Missouri, A. millefolium millefolium, which can be differentiated from this subspecies by a broader, more flat-topped inflorescence.
This second subspecies may have two forms, one with pink or rose colored flowers, and a second with white flowers, glabrous or slightly hairy stems, and glabrous to slightly hairy lanceolate to ovate leaves.
Of course there are cultivars of Achillea out there. One yellow flowered plant is named Achillea Moonshine and looks like this:

Photographs taken at Hermes Nursery, Kansas City, Kansas, 07-14-00, and in the Ozark Scenic Riverways, Shannon County, MO., 5-24-03 and 6-16-05.