Blunt Spikerush Eleocharis obtusa
Blunt Spikerush is an annual grass native to Canada, Hawaii, and the lower 48 states. It grows to 1.6 ft and blooms Jul in part shade – shade, with brown fruit.
More about this plant
Eleocharis obtusa is a species of spikesedge known by the common name blunt spikerush. This plant is widely distributed across Canada and the United States, where it grows in wet areas such as riverbanks and moist forest floors. It is also a weed of rice paddies, especially when the rice plants are young sprouts. This is an annual spikesedge approaching half a meter in maximum height. It has many green cylindrical stems which are erect but weak and spongy. There may be thin, grasslike leaves toward the base of the plant, which are generally straw-colored. Atop each stem is a rounded or oblong spikelet containing at least ten flowers, each covered by an oval-shaped brown bract. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Part shade – shade
- Soil & moisture
- Medium moisture
- Soil pH
- 4.1–8.7
- Fertility need
- Medium
- Adapts to
- Coarse (sandy), Medium (loam), Fine (clay)
- Hardiness
- USDA zone 11+
- Height
- 1.6 ft
- Spacing
- 3–4 ft apart from USDA planting density
- Spread
- Moderate
- Growth rate
- Moderate
- Growth form
- Rhizomatous
- Lifespan
- Annual · short-lived
- Foliage
- Broadleaf · fine texture
- Active growth
- Spring
- Fruit
- Brown persists into winter
- 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
- Spring – Autumn seed-collection / harvest window
- In the trade
- Routinely available
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts Documented caterpillar host
Recorded feeding on Eleocharis in North America, including:
Related plants
More Eleocharis →
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 (33) 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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