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Onagraceae family

Smooth Spike-primrose Epilobium pygmaeum

Native
Also known as: smooth willowweed

Smooth Spike-primrose is an annual wildflower native to Canada and the lower 48 states. It blooms May – Jul.

More about this plant

Epilobium pygmaeum is a species of willowherb known by the common names pygmy willowherb, smooth spike-primrose and smooth boisduvalia. This plant is native to western North America from Baja California to Saskatchewan. It is a resident of vernal pools and mudflats. This is an annual rarely reaching half a meter in height. It is densely foliated in thick green leaves which are hairless lower on the stems and velvety to hairy toward the tips of the branches. The inflorescences at the ends of the stems are dense with small, pointed leaves between which the flowers emerge. Many of the flowers are cleistogamous, meaning they self-pollinate without opening, while others open to reveal four bright pink darkly veined notched petals. The fruit is a small capsule a few millimeters long. Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 4 derived from its U.S. range
Size & form
Sources · Size & form
USDA PLANTS — Lifespan
Lifespan
Annual
In the garden
Herb layer — Sits in the herb of a layered food forest or polyculture.Open guide →
derived roles
The garden year bloom → fruit → fall colour
J
F
M
A
M
J
J
A
S
O
N
D
Bloom
Bloom (the flower's colour)
Bloom · May – Jul — 20 obs · Herbarium specimens — Park et al. 2023 (CC BY 4.0)
Species characteristics from USDA PLANTS (public domain) + TRY (CC BY) — general guidance, not a guarantee for your exact site. Deer "browsing" is documented palatability, not a deer-proof claim.

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.

Keystone count (genus-level) from Warren II 2026 (CC0) · Tallamy host-use records. Named species (a documented Nearctic sample, not exhaustive) from NHM HOSTS (CC0).
Species thumbnails re-hosted from iNaturalist — Creative Commons, credited per image (hover for credit). Click any species to see it on iNaturalist. Not exhaustive; many taxa have no openly-licensed photo yet.
Sources for this entry (12) Open & cited
[01] Scientific name & family — USDA PLANTS (DwCA, Zenodo 17903503)
[02] Growth habit & duration — USDA PLANTS (DwCA, Zenodo 17903503)
[03] Native status & distribution — USDA PLANTS (DwCA, Zenodo 17903503)
[04] Common name — USDA PLANTS (via GBIF)
[05] Invasive / introduced status — USDA PLANTS (DwCA, Zenodo 17903503) — native status
[06] Description — Wikipedia (CC BY-SA)
[07] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts
[09] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[10] Other common names — Wikidata (CC0)
[11] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[12] Caterpillar species — NHM HOSTS (CC0)
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