North America Native Plant

Oahu Flatsedge

Botanical name: Cyperus hypochlorus var. kauaiensis

USDA symbol: CYHYK

Life cycle: perennial

Habit: grass

Native status: Native to Hawaii  

Oahu Flatsedge: A Rare Hawaiian Native Sedge Worth Knowing Meet the Oahu flatsedge (Cyperus hypochlorus var. kauaiensis), a little-known native Hawaiian sedge that represents the unique botanical heritage of the Hawaiian Islands. This perennial grass-like plant belongs to the sedge family and offers a glimpse into Hawaii’s specialized native flora. ...

Oahu Flatsedge: A Rare Hawaiian Native Sedge Worth Knowing

Meet the Oahu flatsedge (Cyperus hypochlorus var. kauaiensis), a little-known native Hawaiian sedge that represents the unique botanical heritage of the Hawaiian Islands. This perennial grass-like plant belongs to the sedge family and offers a glimpse into Hawaii’s specialized native flora.

What Makes This Plant Special?

The Oahu flatsedge is a true Hawaiian endemic, meaning it naturally occurs nowhere else on Earth except in Hawaii. As a member of the sedge family (Cyperaceae), it’s technically not a grass, though it might look grass-like to the casual observer. Sedges are distinguished from true grasses by their triangular stems and different flower structures.

Where Does It Grow?

This native sedge is found exclusively in Hawaii, making it part of the islands’ precious endemic plant community. Its limited geographic distribution underscores the importance of protecting Hawaii’s unique ecosystems.

Should You Grow Oahu Flatsedge?

Here’s where things get interesting – and a bit challenging. Due to the limited information available about this particular variety, it appears to be quite rare or restricted to specific habitats. This rarity presents both an opportunity and a responsibility for native plant enthusiasts.

The Conservation Angle

If you’re considering growing this plant, it’s crucial to source it responsibly. Never collect plants from the wild, as this can harm already vulnerable populations. Instead:

  • Work with reputable native plant nurseries that specialize in Hawaiian species
  • Contact local native plant societies or botanical gardens for guidance
  • Consider participating in conservation efforts rather than private cultivation
  • Choose more common native alternatives if this species isn’t readily available

Growing Conditions and Care

Since specific cultivation information for this variety is limited, general sedge care principles likely apply. Most Hawaiian native sedges prefer:

  • Consistent moisture (many are associated with wetland or riparian areas)
  • Well-draining soil that doesn’t become waterlogged
  • Partial to full sun exposure
  • Protection from strong winds

However, without more specific information about this particular variety’s habitat preferences, successful cultivation may require some experimentation and careful observation.

The Bigger Picture

The Oahu flatsedge represents something larger than just another plant for your garden. It’s a living piece of Hawaiian natural history, shaped by millions of years of isolation and evolution. Whether or not you can grow it in your garden, learning about plants like this helps us appreciate the incredible diversity and fragility of island ecosystems.

Native Alternatives

If you’re drawn to native Hawaiian sedges but can’t locate this specific variety, consider these alternatives:

  • Other Cyperus species native to Hawaii
  • Native Hawaiian grasses and grass-like plants
  • Consult with local native plant experts for region-appropriate recommendations

Remember, the best native garden is one that supports local ecosystems while being sustainable and responsible. Sometimes that means admiring rare plants from afar while cultivating their more common cousins at home.

Oahu Flatsedge

Classification

Group

Monocot

Kingdom

Plantae - Plants

Subkingdom

Tracheobionta - Vascular plants

Superdivision

Spermatophyta - Seed plants

Division

Magnoliophyta - Flowering plants

Subdivision
Class

Liliopsida - Monocotyledons

Subclass

Commelinidae

Order

Cyperales

Family

Cyperaceae Juss. - Sedge family

Genus

Cyperus L. - flatsedge

Species

Cyperus hypochlorus Hillebr. - Oahu flatsedge

Plant data source: USDA, NRCS 2025. The PLANTS Database. https://plants.usda.gov,. 2/25/2025. National Plant Data Team, Greensboro, NC USA