White Alder Alnus rhombifolia
White Alder is a perennial tree native to the lower 48 states. It grows to 65 ft and blooms Oct in full sun, with brown fruit. A keystone plant for native insects and the food web.
More about this plant
Alnus rhombifolia, the white alder, is an alder tree native to western North America, from British Columbia and Washington east to western Montana, southeast to the Sierra Nevada, and south through the Peninsular Ranges and Colorado Desert oases in Southern California. It occurs in riparian zone habitats at an altitudes range of 100–2,400 metres (330–7,870 ft). While not reported in northern Baja California, it has been predicted on the basis of its climatic adaptation to occur there also. Alnus rhombifolia is primarily found in the chaparral and woodlands, montane, and temperate forests ecoregions. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Full sun
- Soil & moisture
- High moisture
- Soil pH
- 4.8–7.5
- Fertility need
- Low
- Adapts to
- Coarse (sandy), Medium (loam), Fine (clay)
- Hardiness
- USDA zone 5+
- Drought tolerance
- Low
- Shade tolerance
- Low
- Wet-soil tolerance
- Moderate waterlogging
- Height
- 65 ft
- Mature width
- ~ 54 ft wide DERIVED derived estimate — open-grown crown allometry (height × growth-form ratio); not a measurement
- Spacing
- 10–30 ft apart from USDA planting density
- Spread
- None — clumping
- Growth rate
- Rapid
- Growth form
- Multiple stems
- Lifespan
- Perennial · long-lived
- Foliage
- Deciduous broadleaf · medium texture
- Active growth
- Spring & summer
- Fruit
- Brown persists into winter
- Propagate by
- Seed, Cuttings, Bare root, Container
- Seed starting
- No stratification needed
- Seeds ripen
- Summer seed-collection / harvest window
- In the trade
- Routinely available
- Deer browsing
- Low often deer-resistant
- Resprouts if cut
- Yes regrows after top-kill
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~255 caterpillar species · keystone genus
Alnus supports ~255 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 powerhouse genus.
Recorded feeding on Alnus in North America, including:
+ 8 more species → ↑ show fewer
Wildlife & visitors 2 nectaring
Open records of who else uses White Alder — a generalist food-web signal, kept separate from the keystone Ecological Value.
2 adult butterfly & moth species are recorded nectaring at its flowers:
Related plants
More Alnus →
How we know this (4) Methods & honest limits
We read each species’ measured specific leaf area (leaf area per unit dry weight) from the Global Spectrum dataset and band it: thin & fast (high SLA), medium, or thick & tough (low SLA). The global median is about 10 mm²/mg.
Honest limits: A species-mean from pooled measurements — individual plants vary with light and site. A broad strategy signal, not a precise per-plant figure.
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.
For woody plants that have a height but no measured crown, we estimate width = height × a crown-to-height ratio fit for that plant’s form (conifers narrower than broadleaf trees, shrubs widest), calibrated on our measured open-grown crowns and capped at the largest one ever measured. A measured crown always wins; herbaceous plants get nothing (no anchor).
Honest limits: A coarse class-median estimate for garden-scale spacing, not a measurement; woody single/multi-stem forms only.
Sources for this entry (36) 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).
Loading…
BibTeX
Loading…