North America Native Plant

Oregon Western Rosinweed

Botanical name: Calycadenia truncata microcephala

USDA symbol: CATRM

Life cycle: annual

Habit: forb

Native status: Native to the lower 48 states  

Oregon Western Rosinweed: A Rare California Native Worth Protecting If you’re passionate about native California plants and conservation, you might be intrigued by Oregon western rosinweed (Calycadenia truncata microcephala). This little-known annual wildflower represents one of those special native plants that deserves our attention—not just for its beauty, but for ...

Rare plant alert!

Region: Conservation status by state

Status: S4T1: Status is uncertain but is somewhere between the following rankings: Subspecies or variety is 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) ⚘ Apparently Secure: Uncommon but not rare, and usually widespread. Possibly cause for longterm concern. Typically more than 100 occurrences in the state or more than 10,000 individuals ⚘

Oregon Western Rosinweed: A Rare California Native Worth Protecting

If you’re passionate about native California plants and conservation, you might be intrigued by Oregon western rosinweed (Calycadenia truncata microcephala). This little-known annual wildflower represents one of those special native plants that deserves our attention—not just for its beauty, but for its rarity and ecological importance.

What Makes Oregon Western Rosinweed Special?

Oregon western rosinweed is a native annual forb that belongs to California’s rich botanical heritage. As an herbaceous plant without woody stems, it completes its entire life cycle in a single growing season, making it a true annual wildflower. This delicate plant is part of the sunflower family and shares the resilient spirit of many California natives.

Where You’ll Find This Rare Beauty

This special plant calls California home, where it grows naturally in the state’s diverse landscapes. However, finding Oregon western rosinweed in the wild requires some luck—it has a Global Conservation Status of S4T1, indicating it’s quite rare and needs our protection.

Important Conservation Considerations

Before we dive into growing tips, let’s address the elephant in the room: rarity. Oregon western rosinweed’s conservation status means this isn’t a plant you should casually collect from the wild or purchase from questionable sources. If you’re interested in growing this native beauty, here’s what you need to know:

  • Only obtain seeds or plants from reputable native plant societies or nurseries
  • Ensure any material is responsibly sourced and legally obtained
  • Consider supporting conservation efforts for rare California natives
  • Remember that growing rare plants comes with responsibility

Garden Role and Landscape Potential

As a native annual forb, Oregon western rosinweed would fit beautifully into:

  • Native wildflower meadows
  • Restoration projects
  • California native plant gardens
  • Conservation-focused landscapes

Its annual nature means it will complete its life cycle in one season, potentially self-seeding for future years if conditions are right.

Growing Conditions and Care

While specific growing requirements for this rare plant aren’t well-documented, we can make educated guesses based on its California native status and annual growth habit:

  • Climate: Likely thrives in USDA zones 8-10, matching California’s Mediterranean climate
  • Soil: Probably prefers well-draining soils typical of California grasslands
  • Water: As a California native annual, it likely follows the state’s natural rainfall patterns
  • Sunlight: Most likely prefers full sun to partial shade

Planting and Care Tips

If you’re fortunate enough to obtain responsibly sourced seeds:

  • Plant seeds in fall to match California’s natural growing season
  • Provide minimal supplemental water once established
  • Allow plants to complete their life cycle and drop seeds naturally
  • Avoid disturbing areas where plants are established
  • Keep detailed records for conservation purposes

Supporting Pollinators and Wildlife

While specific pollinator relationships aren’t well-documented for this rare species, most members of the sunflower family support various native bees, butterflies, and other beneficial insects. By growing Oregon western rosinweed, you’re likely providing habitat for California’s native pollinators.

The Bottom Line

Oregon western rosinweed represents the fascinating world of California’s rare native plants. While its rarity means it’s not suitable for every garden, it offers dedicated native plant enthusiasts a chance to participate in conservation efforts. If you choose to grow this special plant, remember that you’re becoming a steward of California’s botanical heritage.

Consider this plant if you’re passionate about rare natives and committed to responsible gardening practices. Just remember: with rarity comes responsibility, and every rare plant in cultivation is a small victory for conservation.

Oregon Western Rosinweed

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

Asterales

Family

Asteraceae Bercht. & J. Presl - Aster family

Genus

Calycadenia DC. - western rosinweed

Species

Calycadenia truncata DC. - Oregon western rosinweed

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