North America Native Plant

Smooth Cyanea

Botanical name: Cyanea glabra

USDA symbol: CYGL5

Life cycle: perennial

Habit: shrub

Native status: Native to Hawaii  

Synonyms: Cyanea holophylla Hillebr. var. obovata Rock (CYHOO)  âš˜  Cyanea knudsenii Rock var. glabra E. Wimm. (CYKNG)  âš˜  Cyanea scabra Hillebr. var. variabilis Rock p.p. (CYSCV)   

Smooth Cyanea: A Rare Hawaiian Treasure Worth Protecting If you’re passionate about native plants and conservation, you might have heard whispers about the smooth cyanea (Cyanea glabra). This stunning Hawaiian native is more than just another pretty face in the tropical plant world – it’s a living piece of Hawaii’s ...

Rare plant alert!

Region: United States

Status: S1: Status is uncertain but is somewhere between the following rankings: Critically Imperiled: Extremely rare due to factor(s) making it especially vulnerable to extinction. Typically 5 or fewer occurrences or very few remaining individuals (<1,000) ⚘ Endangered: In danger of extinction throughout all or a significant portion of its range. ⚘

Region: United States

Smooth Cyanea: A Rare Hawaiian Treasure Worth Protecting

If you’re passionate about native plants and conservation, you might have heard whispers about the smooth cyanea (Cyanea glabra). This stunning Hawaiian native is more than just another pretty face in the tropical plant world – it’s a living piece of Hawaii’s natural heritage that desperately needs our help.

What Makes Smooth Cyanea Special?

Smooth cyanea is a perennial shrub that’s part of the bellflower family, and boy, does it know how to make an entrance! This multi-stemmed beauty typically grows less than 13-16 feet tall, with several stems arising from near the ground. What really sets it apart are its distinctive tubular flowers that were perfectly designed by nature to attract Hawaii’s native honeycreeper birds.

You might also see this plant listed under its scientific synonyms, including Cyanea holophylla var. obovata or Cyanea knudsenii var. glabra, but don’t let the fancy names fool you – we’re talking about the same remarkable plant.

Where Does Smooth Cyanea Come From?

This gorgeous shrub is endemic to Hawaii, meaning you won’t find it growing wild anywhere else on Earth. It’s a true island original that has evolved specifically to thrive in Hawaiian conditions.

The Reality Check: Why This Plant Needs Your Help

Here’s where things get serious, folks. Smooth cyanea isn’t just rare – it’s critically imperiled with a Global Conservation Status of S1. In plain English? This plant is hanging on by a thread. With typically 5 or fewer occurrences and fewer than 1,000 individuals remaining in the wild, it’s officially listed as Endangered in the United States.

This means if you’re considering adding smooth cyanea to your garden, you absolutely must source it responsibly. We’re talking about purchasing from reputable nurseries that propagate from legally obtained, conservation-approved stock – never from wild-collected plants.

Should You Grow Smooth Cyanea?

If you live in USDA hardiness zones 10-12 and are committed to conservation, growing smooth cyanea can be incredibly rewarding. Here’s what you need to know:

The Good News

  • You’ll be directly contributing to species conservation
  • Unique aesthetic appeal with distinctive tubular flowers
  • Perfect for native Hawaiian or tropical shade gardens
  • Excellent conversation starter about Hawaiian ecology

The Challenges

  • Very limited availability from ethical sources
  • Requires specific tropical growing conditions
  • Can be finicky about environmental requirements
  • May need greenhouse protection outside of Hawaii

How to Grow Smooth Cyanea Successfully

If you’ve managed to source this rare beauty responsibly, here’s how to give it the best chance of thriving:

Growing Conditions

  • Provide partial to full shade – think understory conditions
  • Ensure consistently moist, well-draining soil
  • Maintain high humidity levels
  • Protect from strong winds
  • Keep temperatures consistently warm (zones 10-12 only)

Care Tips

  • Water regularly but avoid waterlogged conditions
  • Use organic mulch to retain moisture and suppress weeds
  • Consider greenhouse cultivation if you’re not in Hawaii
  • Monitor closely for any signs of stress

Garden Design Role

Smooth cyanea works beautifully as an accent plant in native Hawaiian gardens or as a special specimen in tropical shade gardens. Its unique form and flowers make it perfect for conservation-focused landscapes where every plant tells a story about Hawaii’s incredible biodiversity.

The Bottom Line

Growing smooth cyanea isn’t for everyone, and that’s okay. This critically endangered plant requires serious commitment, specific growing conditions, and – most importantly – ethical sourcing. If you’re up for the challenge and can source it responsibly, you’ll be participating in conservation efforts while enjoying one of Hawaii’s most unique native plants.

Remember, every smooth cyanea grown in cultivation is potentially one more step back from extinction. Just make sure you’re doing it right – this remarkable plant deserves nothing less than our most responsible efforts.

Smooth Cyanea

Classification

Group

Dicot

Kingdom

Plantae - Plants

Subkingdom

Tracheobionta - Vascular plants

Superdivision

Spermatophyta - Seed plants

Division

Magnoliophyta - Flowering plants

Subdivision
Class

Magnoliopsida - Dicotyledons

Subclass

Asteridae

Order

Campanulales

Family

Campanulaceae Juss. - Bellflower family

Genus

Cyanea Gaudich. - cyanea

Species

Cyanea glabra (E. Wimm.) H. St. John - smooth cyanea

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