According to observations of naturalists and beekeepers.
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Toxic for bees
SOURCE FOR HONEY BEES:
California buckeye is endemic to California. It occurs in the Klamath and Coast Ranges from Siskiyou County south to Los Angeles County. In the Cascade Range and the foothills of the Sierra Nevada, it occurs from Shasta County south to Kern County. California buckeye is occasionally found in the Central Valley in Yolo, Colusa, and Stanislaus Counties.
This plant is present in at least 2 states/provinces in this country.
California buckeye is a large shrub or tree up to 23 feet (7 m) tall. The 2-to 6-inch-long (5-15 cm) leaves are deciduous and palmately compound. Flowers are borne on a terminal panicle 4 to 8 inches (10-20 cm) long. The pear-shaped, light brown fruit contains one to six glossy brown seeds 0.8 to 1.2 inches (2-3 cm) in diameter.
The bark, leaves, and fruits contain the neurotoxic glycoside aesculin, which causes hemolysis of red blood cells.
California buckeye flowers from April to September. The nectar of the flowers is toxic to the Asian/European honeybee, so the trees should not be planted near apiaries.
New leaves emerge from March to June while soil moisture is abundant. Fruits ripen from September to October and are dropped from November to December.
Brassica napus (aka: Rapeseed)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Asclepias tuberosa (aka: Butterflyweed, Butterfly Milkweed, Orange Milkweed, Pleurisy Root, Chigger Flower, Canada root, Fluxroot, Indian paintbrush, Indian posy, Orange root, Orange Swallow-wort, Tuber root, Yellow milkweed, White-root, Windroot, Butterfly love)
Calendula officinalis (aka: Marigold, Calendula, Pot marigold, English marigold)
Cucumis melo (aka: Cantaloupe, Rockmelon, Sweet melon, Spanspek, Honeydew melon, Honeymelon, Crenshaw, Casaba)
Citrullus lanatus (aka: Watermelon)
Cirsium arvense (aka: Creeping Thistle, Canada thistle, Field thistle, California thistle, Lettuce from hell thistle, Corn thistle, Cursed thistle, Green thistle, Hard thistle, Perennial thistle, Prickly thistle, Small-flowered thistle, Way thistle, Stinger-needles)
Borago officinalis (aka: Borage, Starflower, Common borage, Cool-tankard, Tailwort)