North America Non-native Plant

Cape Marigold

Botanical name: Castalis tragus

USDA symbol: CATR18

Life cycle: perennial

Habit: subshrub

Native status: Non-native, reproduces and persists in the wild in the lower 48 states  

Synonyms: Dimorphotheca aurantiaca DC., non Horton (DIAU3)   

Cape Marigold: What We Know About This Mysterious Non-Native Perennial Meet Castalis tragus, commonly known as Cape marigold – a plant that’s managed to keep quite a few secrets from gardeners and botanists alike. While many plants have detailed profiles and growing guides, this particular species is a bit of ...

Cape Marigold: What We Know About This Mysterious Non-Native Perennial

Meet Castalis tragus, commonly known as Cape marigold – a plant that’s managed to keep quite a few secrets from gardeners and botanists alike. While many plants have detailed profiles and growing guides, this particular species is a bit of an enigma in the gardening world.

The Basics: What Is Cape Marigold?

Cape marigold (Castalis tragus) is a perennial forb, which simply means it’s a non-woody plant that comes back year after year. Unlike shrubs or trees, forbs like this one lack significant woody tissue and keep their growing points at or below ground level – a smart survival strategy that helps them weather tough conditions.

You might also see this plant listed under its synonym, Dimorphotheca aurantiaca, which can add to the confusion when you’re trying to research it. Plant names can be tricky that way!

Where You’ll Find It

Currently, Cape marigold has established itself in Arizona, where it reproduces on its own without human intervention. As a non-native species that’s been introduced to the United States, it represents one of many plants that have found a new home far from their original habitat.

The Challenge of Growing Cape Marigold

Here’s where things get interesting – and a bit frustrating for curious gardeners. Despite its intriguing name and perennial nature, there’s surprisingly little detailed information available about Cape marigold’s specific growing requirements, appearance, or garden performance. This lack of information presents both a challenge and an opportunity.

What We Don’t Know (Yet)

The mystery surrounding Cape marigold extends to many practical gardening aspects:

  • Specific growing conditions and soil preferences
  • Mature height and spread
  • Flower characteristics and bloom time
  • USDA hardiness zones
  • Propagation methods
  • Benefits to pollinators and wildlife
  • Invasive potential

A Gardener’s Dilemma

Without detailed growing information, it’s difficult to recommend Cape marigold for specific garden situations. The lack of available data about its invasive potential also makes it challenging to assess whether it’s a responsible choice for your landscape.

Consider Native Alternatives

Given the uncertainty surrounding Cape marigold and its non-native status, you might want to explore native alternatives that can provide similar benefits with well-documented growing requirements. Native plants offer several advantages:

  • Proven compatibility with local ecosystems
  • Better support for native wildlife and pollinators
  • Adaptation to local climate and soil conditions
  • Extensive growing information and support resources

Consider researching native perennial forbs in your area that might fill the same garden niche you’re hoping Cape marigold would occupy.

The Bottom Line

Cape marigold remains something of a botanical puzzle – a plant that exists in our landscapes but hasn’t revealed all its secrets to gardeners. While its perennial nature and ability to establish in Arizona suggest it has some garden potential, the lack of detailed information makes it difficult to recommend with confidence.

If you’re drawn to the mystery and happen to encounter Cape marigold, proceed with caution and keep detailed records of its behavior in your garden. You might just become one of the few gardeners to document this elusive plant’s growing habits!

For now, though, your garden – and local ecosystem – might be better served by choosing well-documented native alternatives that can provide beauty, ecological benefits, and peace of mind.

Cape Marigold

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

Castalis Cass. - castalis

Species

Castalis tragus (Aiton) Norl. - Cape marigold

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