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Asteraceae family

Slough Thistle Cirsium crassicaule

Native Specialist-bee host

Slough Thistle is an annual wildflower native to the lower 48 states. It blooms May. A host for pollen-specialist native bees.

More about this plant

Cirsium crassicaule is a species of thistle known by the common name slough thistle. It is endemic to the San Joaquin Valley of California, where it is known primarily from freshwater wetlands. It has been found in only a few locations in Kern, Kings, and San Joaquin Counties. Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 11 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 →
Rain garden / bioswale — Rated OBL on the wetland list — tolerates wet feet, so it suits the soggy zone of a rain garden or bioswale that catches and filters runoff.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 — 13 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 ~29 caterpillar species

Cirsium supports ~29 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 moderate genus.

Recorded feeding on Cirsium in North America, including:

Anagrapha falcifera · Celery Looper Autographa precationis · Common Looper Calephelis mutica · Swamp Metalmark Calephelis virginiensis · Little Metalmark Cnephasia longana · leafroller moth Dicymolomia julianalis · Julia's Dicymolomia
+ 8 more species →
Endopiza viteana · leafroller moth Euxoa auxiliaris · Army Cutworm Moth Hedya cyanana · leafroller moth Homoeosoma ammonastes · snout moth Homoeosoma ardaloniphas · snout moth Homoeosoma electella · Sunflower Moth Homoeosoma eremophasma · snout moth Homoeosoma impressale · snout moth
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).
✦ Bees specialist-bee host · 37 bee visitors

Specialist native bees depend on it.

Some native bees are pollen specialists (oligolectic) — they raise young only on pollen from particular plant genera. Cirsium is a recorded specialist-bee host, so losing it can mean losing the bee that relies on it.

Xerces pollinator conservation →

37 native & managed bee species are documented visiting Slough Thistle — the 12 most-recorded:

Agapostemon femoralis · sweat bee Agapostemon sericeus · Silky Agapostemon Agapostemon texanus · Texas Agapostemon Anthophora walshii · Walsh's Anthophora Apis mellifera · Honey Bee Bombus auricomus · Black And Gold Bumble Bee
+ 6 more bees →
Bombus fraternus · Southern Plains Bumble Bee Bombus griseocollis · Brown-Belted Bumblebee Bombus impatiens · Common Eastern Bumblebee Bombus pensylvanicus · Sonoran Bumblebee Bombus vagans · Half-Black Bumblebee Bombus variabilis · Variable Cuckoo Bumblebee
Specialist hosts from Smith et al. 2024. Visitor records (observations, not exhaustive) from Noori et al. 2026 (CC BY 4.0) · GloBI →
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 (16) 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] Wetland indicator — USACE National Wetland Plant List (2022)
[08] Description — Wikipedia (CC BY-SA)
[09] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts · Smith et al. 2024 (CC BY)
[11] Conservation rank — NatureServe Explorer (CC BY)
[12] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[14] Flower-visitor value (derived) — Noori et al. 2026 (CC BY 4.0) · GloBI
[15] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[16] Caterpillar species — NHM HOSTS (CC0)
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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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