Mertens' Rush Juncus mertensianus
Mertens' Rush is a perennial grass native to Alaska, Canada, and the lower 48 states. It grows to 0.9 ft and blooms May in full sun – part shade, with brown fruit.
More about this plant
Juncus mertensianus is a species of rush known by the common name Mertens' rush or Alaska rush. It is native to much of western North America from Alaska to Saskatchewan to New Mexico, where it grows in wet mountainous areas such as riverbanks and alpine meadows. This is a clumping perennial herb growing from a vertical rhizome. Its smooth, flat stems grow to a maximum height near 40 centimeters. Its few leaves are located at the base and also along the stem. The inflorescence is made up of usually one cluster of many flowers. Each flower has shiny dark brown to black tepals 3 to 4 millimeters long, six stamens with yellowish anthers, and long reddish stigmas, as in image at left. The fruit is a dark, oblong capsule, as in image at right. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Full sun – part shade
- Soil & moisture
- High moisture
- Soil pH
- 6–8
- Fertility need
- Medium
- Adapts to
- Coarse (sandy), Medium (loam)
- Hardiness
- USDA zone 4+
- Height
- 0.9 ft
- Spacing
- 3–4 ft apart from USDA planting density
- Spread
- Moderate
- Growth rate
- Moderate
- Growth form
- Rhizomatous
- Lifespan
- Perennial · moderate
- Foliage
- Evergreen broadleaf · fine texture
- Active growth
- Spring & summer
- Fruit
- Brown
- Flower colour
- Brown AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
- Propagate by
- Seed, Bare root, Sprigs
- Seed starting
- No stratification needed
- Seeds ripen
- Summer seed-collection / harvest window
- In the trade
- Routinely available
- Deer browsing
- Medium moderately palatable
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~6 caterpillar species
Juncus supports ~6 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 modest genus.
Recorded feeding on Juncus in North America, including:
+ 8 more species → ↑ show fewer
Across 27 U.S. vegetation-survey plots that recorded Mertens' Rush, these catalog species turned up most often in the same plot — a real field co-occurrence signal, not a planting prescription.
Related plants
More Juncus →
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 (34) 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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