Washerwoman Alternanthera caracasana
Washerwoman is a perennial wildflower native to Puerto Rico and the U.S. Virgin Islands. It blooms Jun – Dec.
More about this plant
Alternanthera caracasana is a species of flowering plant in the family Amaranthaceae known by the common names khakiweed, washerwoman and mat chaff flower. It is native to Central and South America but is well-known elsewhere as a noxious weed. It is naturalized in some areas and invasive in others and can be found across the southern half of the United States, Australia, Spain and parts of Africa. The plant has long, prostrate stems covered in small leaves which vary in shape from diamond to rounded. It grows from a rhizome and often roots from its lower nodes. Each spike inflorescence is under a centimeter wide and is covered in tiny stiff white flowers. This is a tough weed of lots, roads, railroad tracks, cleared areas, and other places that are rough, sandy, and often well-traveled. Wikipedia →
Growing & care
USDA PLANTS · TRY- Hardiness
- ≥ zone 8 derived from its U.S. range
- Lifespan
- Perennial
- Foliage
- Broadleaf
- Flower colour
- Brown AI AI image-analysis of community-science photos — lower-confidence (a more subjective call, often an inconspicuous flower); not a botanical record
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~4 caterpillar species
Alternanthera supports ~4 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a modest genus.
Recorded feeding on Alternanthera in North America, including:
Related plants
More Alternanthera →
How we know this (3) Methods & honest limits
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
McKenzie et al. assigned each species a flower colour with a GPT-4V vision model over iNaturalist photos. We use the confident tier plus a separately-labelled lower-confidence top-up (mostly inconspicuous green/brown flowers), and render it as a small tint — never as an asserted fact, and kept out of the written synopsis.
Honest limits: AI image inference (~87% expert agreement on the confident tier); a decorative, confidence-tiered indicator, not a measured trait.
Sources for this entry (19) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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