Rockfringe Epilobium obcordatum
Rockfringe is a perennial shrub native to the lower 48 states. It blooms Jul – Sep.
More about this plant
Epilobium obcordatum is a species of perennial plant in the evening-primrose family (Onagraceae), known by the common name rockfringe willowherb and rock fringe. It is native to the western United States from California to Idaho, where it is found in rocky mountainous areas, at altitudes of 7,000 ft (2,100 m) to 13,000 ft (4,000 m). This small perennial is clumpy to mat-forming and spreads from a woody caudex, especially in nooks between rocks. It has stems lined with oval or rounded leaves which spread parallel to the ground or ascend somewhat. At the tips of the thin stems are flowers each with four petals. The petals are magenta to purple, rounded and notched, often in a perfect heart shape, and are one or two centimeters long. The glandular, club-like, ridged fruit is a capsule two to four centimeters long growing on a short stalk. Wikipedia →
Growing & care
USDA PLANTS · TRY- Hardiness
- ≥ zone 7 derived from its U.S. range
- Lifespan
- Perennial
- Flower colour
- Purple AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~32 caterpillar species
Epilobium supports ~32 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 strong genus.
Recorded feeding on Epilobium in North America, including:
+ 8 more species → ↑ show fewer
Related plants
More Epilobium →
How we know this (2) Methods & honest limits
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 (17) 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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