Mayweed chamomile (Anthemis cotula)
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Mayweed chamomile, often called dog fennel, is an annual bushy broadleaf plant that germinates in early spring. In California it is found in the northwestern region, central-western region, central Sierra Nevada, Central Valley, South Coast, Transverse Ranges, and Peninsular ranges up to 6600 feet (about 2000 m). Mayweed chamomile inhabits agricultural land and other disturbed areas.
Coastal dunes, chaparral, woodlands, crop fields, orchards, vineyards, landscaped areas, gardens, roadsides and other disturbed, unmanaged sites.
Although they dry up rapidly and are seldom seen, the cotyledons (seed leaves) are oval, hairless, and small at roughly 1/10 to 1/3 of an inch (2.5–8 mm) in length. The leaves in the first leaf pair are opposite to one another along the stem and can be nearly hairless to hairy. Subsequent leaves are alternate to one another along the stem, are lobed to deeply divided, and nearly hairless to hairy.
Mayweed chamomile can have a spreading form or be an erect plant, reaching 6 inches to 3 feet (15–90 cm) long. Although similar looking to pre-flowering pineappleweed, Chamomilla suaveolens, and lesser swinecress, Coronopus didymus, mayweed chamomile can be distinguished by its more finely dissected leaves that appear to clasp the stem. Also crushed pineappleweed smells like pineapple whereas crushed mayweed's odor is unpleasant.
Flowering takes place from April to August. Tiny flowers cluster to form a daiseylike flowerhead with white flowers (ray flowers) circling a center of yellow flowers (disc flowers).
Fruits are single seeded, wedge shaped, and ribbed.
Mayweed chamomile reproduces by seed.