Common cocklebur (Xanthium strumarium)
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Common cocklebur is a coarse summer annual broadleaf plant. It is found throughout California except in the Great Basin and non-irrigated desert areas up to 1640 feet (about 500 m). It inhabits open, often moist disturbed places in agricultural land and other areas. Ingestion of cocklebur seedlings and seeds at 1% or more of body weight can be fatal to livestock.
Roadsides, ditches, valley bottomlands, pastures, cultivated crop fields, orchards, riparian areas, seasonal wetlands and disturbed, unmanaged places.
Cotyledons (seed leaves) are bright green, shiny on the upper surface, pointed, and about six times longer than they are wide. The stalk below the cotyledon is short, thick, and fleshy. The first true leaves are often opposite to one another on the stem. Later leaves are alternate to one another. Both the first and next few leaf pairs are egg shaped and covered with minute hairlike projections that are rough to the touch. The bur that once contained the seed may remain attached to the base of the seedling, helping to identify the weed when it is pulled. True leaves on the seedlings are notched on the edges and taper toward the leaf tip.
Stems are thick, and may branch many times, and have purple or black spots. Leaves alternate with one another along the stem, are lobed, triangular, coarsely toothed, and have long stalks. Leaves have a distinctive scent.
Flowers bloom from July through October. Clusters of small green to rusty red male flower heads develop where the upper leaf stalk meets the stem (leaf axil). Female flowers develop below the male flower heads in oval-shaped burs with short stalks.
Fruits are football shaped prickly burs mostly 3/5 to 1-2/5 inches (1.5–3.5 cm) long. The burs are green to yellowish and have a pair of beaklike hooks at the tip.
Two seeds are enclosed in each bur, one larger than the other.
Reproduces by seed.