Flower:

Daisy-type flowers, single at the tips of branching stems. Flowers are ½ to 1 inch across with 10 to 25 white petals (ray flowers) and a yellow to greenish-yellow center disk that expands from button-shaped to dome-shaped as it matures. The disk is hollow at the core.

The bracts surrounding the base of the flower are in 3 layers, narrowly lance-oblong, green with membranous edging. Bracts and flower stalks are hairless.

Leaves and stems:

Leaves are ½ to 3 inches long, feathery with a few to numerous thread-like branching lobes. Stems are usually multiple from the base, erect to ascending, many branched in the upper plant, ribbed or lined, and hairless. Plants are aromatic when bruised.

Fruit:

The center disk becomes a round head of dry, gray-brown seed that lack tufts of hair. Seeds are less than 1mm long, cone-shaped to oblong, round in cross-section, have 3 to 5 white ribs, and gland-dotted (magnification required).

Notes:

German Chamomile, also known as Matricaria recutita, has a long history of medicinal uses, cultivated globally and occasionally escapes cultivation but is not known to invade high quality habitat. Of similar species, the related Pineapple-weed (M. discoidea) lacks ray flowers, Dog Fennel (Anthemis cotula) leaves have broader and flatter lobes and a distinct, unpleasant odor when crushed, and Scentless False Mayweed (Tripleurospermum inodorum) has larger flowers with a solid core on the disk and is not aromatic. Feel free to rip the disks open and see whether they're hollow or solid. These are all weeds, after all.