Flower:

Daisy-type flowers, single at the tips of branching stems. Flowers are 1 to 2 inches across with 10 to 25 white petals (ray flowers) and a golden yellow center disk that expands from button-shaped to dome-shaped to nearly round as it matures. The rays droop as the disk expands, bent straight down at maturity before wilting away. The disk is solid at the core.

The bracts surrounding the base of the flower are narrowly lance-oblong, darker green to brownish down the center with a narrow band of pale membranous edging but darker brown at the tip. Bracts and flower stalks are hairless, sometimes sparsely hairy when young.

Leaves and stems:

Leaves are ¾ to 3 inches long, feathery with a few to numerous thread-like branching lobes. Stems are single, erect, branched in the upper plant, weakly ridged or lined, hairless though sparsely hairy when young.

Fruit:

The center disk becomes a round head of dry, brown seed that lack tufts of hair. Seeds are triangular in cross-section, have 3 to 5 ribs, and a minutely textured surface between the ribs (magnification required).

Notes:

Scentless False Mayweed, also known by synonyms Matricaria perforata and Tripleurospermum maritimum subsp. inodorum, is similar to the also-weedy Dog Fennel (Anthemis cotula) and Matricaria species. Dog Fennel has leaves that are pinnately lobed (divisions on opposite sides of a common stalk), have broader and flatter lobes, and a distinct, unpleasant odor when crushed. While the Maticaria species have very similar feathery and thread-like leaves, the seeds are not triangular in cross-section and are smooth between the 5 ribs. Also, Pineapple-weed (M. discoidea) lacks ray flowers, and German Chamomile (M. chamomilla a.k.a. M. recutita) has a flower disk with a hollow core and typically has multiple stems. Feel free to rip the disks open and see whether they're hollow or solid. These are all weeds, after all.