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Clethraceae family

Mountain Sweetpepperbush Clethra acuminata

Native

Mountain Sweetpepperbush is a perennial tree native to the lower 48 states. It grows to 20 ft and blooms Jul – Aug.

More about this plant

Clethra acuminata, the mountain pepper bush, is a shrub native to the Appalachian Mountains of the southeastern United States. It has been reported from the states of Pennsylvania, West Virginia, Virginia, North Carolina, South Carolina, Georgia, Alabama and Tennessee, primarily from deciduous forests at elevations of 500–1,400 m (1,600–4,600 ft). Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 7 derived from its U.S. range
Size & form
Sources · Size & form
TRY Plant Trait Database (CC BY 4.0) — Height · Foliage
USDA PLANTS — Lifespan
McKenzie et al. 2025 — community-science image analysis (MIT) — Flower colour
Height
20 ft
Lifespan
Perennial
Foliage
Deciduous broadleaf
Flower colour
White AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
In the garden
Sub-canopy / understory layer — Sits in the understory of a layered food forest or polyculture.Open guide →
derived roles
AI = read by an AI vision model · DERIVED = a computed estimate, not a direct measurement. The “How we know this” section below details each.
The garden year bloom → fruit → fall colour
J
F
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J
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Bloom
Bloom (the flower's colour)
Bloom · Jul – Aug — 15 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 ~10 caterpillar species

Clethra supports ~10 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 Clethra in North America, including:

Ematurga amitaria · Cranberry Spanworm Moth Herpetogramma pertextalis · Bold-Feathered Grass Moth Herpetogramma thestealis · Zigzag Herpetogramma Lymantria dispar · Gypsy Moth Nola clethrae · Sweet Pepperbush Nola Moth Olethreutes inornatana · Inornate Olethreutes
+ 2 more species →
Prochoerodes transversata · geometer (inchworm) moth Pyrrharctia isabella · Isabella Tiger 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 1 bee visitor

1 native & managed bee species is documented visiting Mountain Sweetpepperbush :

Bombus impatiens · Common Eastern Bumblebee
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.
Frequently grows with

Across 101 U.S. vegetation-survey plots that recorded Mountain Sweetpepperbush, these catalog species turned up most often in the same plot — a real field co-occurrence signal, not a planting prescription.

Red Maple · 90% Great Laurel · 78% Mountain Laurel · 76% Northern Red Oak · 67% Beetleweed · 60% American Witchhazel · 57% Eastern Hemlock · 56% Roundleaf Greenbrier · 53%
By region — what it grows with near you
"%" = share of this plant's plots that also held the species. From sPlotOpen → (Sabatini et al. 2021, CC BY 4.0) — open vegetation plots: wild community composition, not garden design.
How we know this (2) Methods & honest limits
Climate niche (heat tolerance & native rainfall) Derived

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.

Realized-niche / climate-envelope approach (Pearson & Dawson 2003; Soberón 2007). Climate: NOAA NCEI nClimDiv county normals (1991–2020).
Flower colour Derived

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.

McKenzie, P., Berardi, A.E., Hopkins, R. (2025). flower_color_phenology (MIT).
Derived values are computed from open data by a published method — labelled, cited, and never shown as a direct observation. Full methodology →
Sources for this entry (21) 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
[07] Description — Wikipedia (CC BY-SA)
[08] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts
[10] Conservation rank — NatureServe Explorer (CC BY)
[13] Climate niche — Derived — realized climate niche from U.S. county occurrences (GBIF) × NOAA NCEI county climate normals 1991–2020 (public domain)
[14] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[17] Flower-visitor value (derived) — Noori et al. 2026 (CC BY 4.0) · GloBI
[18] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[19] Caterpillar species — NHM HOSTS (CC0)
[20] County range — GBIF Open Data — open-licensed occurrences (CC0/CC-BY) → county
Spot an error or have a better photo? Every field links to its source, and the whole dataset is open.
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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