Glaucus Willowherb Epilobium glaberrimum
Glaucus Willowherb is a perennial wildflower native to Canada and the lower 48 states. It grows to 2 ft and blooms Jul in full sun, with white fruit.
More about this plant
Epilobium glaberrimum is a species of willowherb known by the common name glaucous willowherb. This clumping perennial wildflower is native to western North America from central Canada to northern Mexico. It generally grows at some elevation in moist places. This plant is somewhat variable in appearance. It may exceed half a meter in height and has hairless foliage with leaves between one and 8 centimeters long. The flower has four notched petals in purple, pink, or white which may be only a couple of millimeters long to over a centimeter long each. The fruit is a narrow, sticklike capsule 2 to 7 centimeters long. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Full sun
- Soil & moisture
- Medium moisture
- Soil pH
- 6.1–7.5
- Fertility need
- Low
- Adapts to
- Medium (loam), Fine (clay)
- Hardiness
- USDA zone 7+
- Height
- 2 ft
- Spread
- Slow
- Growth rate
- Slow
- Growth form
- Rhizomatous
- Lifespan
- Perennial · moderate
- Foliage
- Broadleaf · medium texture
- Active growth
- Spring & summer
- Fruit
- White
- Flower colour
- Pink AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
- Propagate by
- Seed
- Seed starting
- No stratification needed
- Seeds ripen
- Summer seed-collection / harvest window
- In the trade
- No known commercial source
- Deer browsing
- Low often deer-resistant
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
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 (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 (30) 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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