Common roadside weed confirmed spreading through a California neighborhood
iNaturalist: jordandelarosa
Invasive Species
If you've battled a scraggly, gray-green weed popping up through sidewalk cracks or garden edges in Southern California, this is likely it, and some populations have already outsmarted glyphosate.
Someone spotted a scraggly weed called flax-leaved horseweed growing along a street in Walnut, California, and logged it on iNaturalist with a photo clear enough that other naturalists confirmed the identification. This plant is a close cousin of common horseweed and tends to pop up in disturbed soil like roadsides, vacant lots, and garden edges. It's not rare or exciting on its own, but tracking exactly where it shows up helps scientists and land managers watch how far this weed, which has developed resistance to common herbicides in parts of California, has spread.
Key Findings
Observation achieved 'research-grade' status on iNaturalist, meaning the identification was confirmed by multiple community members
Species identified as Erigeron bonariensis, commonly called flax-leaved horseweed or hairy fleabane
Location recorded as N Tuolumne Dr, Walnut, California, a residential/urban setting typical for this disturbance-loving weed
chevron_right Technical Summary
A citizen scientist documented flax-leaved horseweed, a common weedy plant, growing along a residential street in Walnut, California. The sighting was verified to research-grade status, adding a confirmed data point to tracking where this often herbicide-resistant weed is spreading.
Abstract Preview
Original paper
Flax-leaved Horseweed (Erigeron bonariensis) observed in N Tuolumne Dr, Walnut, CA, US
Research-grade observation of Flax-leaved Horseweed in N Tuolumne Dr, Walnut, CA, US.
open_in_new Read full abstractAbstract copyright held by the original publisher.
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