Mexican brassbuttons  (Cotula Mexicana)

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Mexican brassbuttons is a low growing perennial broadleaf plant that is mostly found growing in the Cascade Range, Sacramento Valley, and the San Francisco Bay region, but is expanding its range. It mainly inhabits turf, is difficult to control there, and has the potential to become a serious weed. Generally it roots deeper than turf grasses, thrives with low clipping practices, and can exclude turf from golf courses. However, it competes poorly with taller vegetation. It spreads rapidly and is easily overlooked because of its small size.

Along with other Cotula species, Mexican brassbuttons has become a “C” rated noxious weed by the California Department of Food and Agriculture.

Habitat

Mexican brassbuttons is found in golf course greens in the counties of Sacramento, Marin, Contra Costa, and Alameda, but can be a problem in any low-mowed turf. It has the potential to become a problem in turf nurseries.

Mature plant

The mature plant is small and has prostrate branching stems with short rhizomes and stolons (below and aboveground creeping stems). Leaves are feathery (dissected) and have a few hairs, except for leaves that collect at branch tips, which are hairless.

Flowers

Green, pale flowers cluster into flower heads called inflorescences that are about 1/12 inch (2 mm) in diameter, with a hairy base (receptacle) and short stalks that about (10 mm) long. Two similar plants, southern brassbuttons, Cotula australis, and brassbuttons, Cotula cornopifolia have non-hairy receptacles. The flowers of southern brassbuttons are yellow to white and those of brassbuttons are bright yellow.

Fruits

Fruit are small achenes (one seeded).

Reproduction

Mexican brassbuttons reproduces by seed and by rhizomes (underground) and stolons (aboveground) creeping stems.

Related or similar plants

• Brassbuttons, Cotula cornopifolia
• Lawn burweed, Soliva sessilis
• Pineappleweed, Chamomilla suaveolens
• Southern brassbuttons, Cotula australis

More information

• Broadleaf ID illustration
• Calflora's distribution map
• See UC IPM's Pest Management Guidelines for Turfgrass for information on management