North America Native Plant

Mona Island Swallow-wort

Botanical name: Cynanchum monense

USDA symbol: CYMO6

Life cycle: perennial

Habit: vine

Native status: Native to Puerto Rico  

Synonyms: Metastelma monense Britton (MEMO8)   

Mona Island Swallow-wort: A Rare Caribbean Treasure Worth Protecting If you’re passionate about native plants and happen to be gardening in Puerto Rico, you might have heard whispers about a mysterious little plant called Mona Island swallow-wort (Cynanchum monense). But before you start planning where to plant this rare beauty, ...

Rare plant alert!

Region: Conservation status by state

Status: S2: Status is uncertain but is somewhere between the following rankings: Imperiled: Extremely rare due to factor(s) making it especially vulnerable to extinction. Typically 6 to 20 occurrences or few remaining individuals (1,000 to 3,000) ⚘

Mona Island Swallow-wort: A Rare Caribbean Treasure Worth Protecting

If you’re passionate about native plants and happen to be gardening in Puerto Rico, you might have heard whispers about a mysterious little plant called Mona Island swallow-wort (Cynanchum monense). But before you start planning where to plant this rare beauty, there’s something important you need to know – this isn’t your typical garden center find.

What Makes This Plant So Special?

Mona Island swallow-wort is what botanists call an endemic species, meaning it exists nowhere else on Earth except in Puerto Rico. This perennial herb belongs to the milkweed family and represents a unique piece of Caribbean botanical heritage. You might also see it listed under its scientific synonym, Metastelma monense, in older botanical references.

Where Does It Call Home?

This remarkable plant is native exclusively to Puerto Rico, with its primary stronghold being the remote Mona Island. As its common name suggests, this tiny island between Puerto Rico and the Dominican Republic is where this species has evolved and adapted to very specific conditions over thousands of years.

Why You Should Think Twice Before Growing It

Here’s where things get serious, fellow plant lovers. Mona Island swallow-wort carries a Global Conservation Status of S2, which means it’s considered Imperiled. In plain English, this plant is hanging on by a thread in the wild, with typically only 6 to 20 known populations and possibly fewer than 3,000 individual plants remaining in existence.

What does this mean for gardeners? While we absolutely encourage growing native plants, this particular species requires special consideration:

  • Only obtain plants or seeds from verified, responsible conservation sources
  • Never collect from wild populations
  • Consider whether your garden can truly provide the specialized conditions this rare plant needs
  • Think about supporting conservation efforts instead of or alongside any cultivation attempts

Growing Conditions and Care

Unfortunately, detailed cultivation information for Mona Island swallow-wort is extremely limited due to its rarity and the fact that few people have successfully grown it outside its natural habitat. What we do know is that as a forb herb, it’s a non-woody perennial plant that likely requires very specific environmental conditions found in its native Puerto Rican ecosystem.

If you’re determined to work with this species, you’ll need to:

  • Consult with local Puerto Rican botanical gardens or conservation organizations
  • Ensure any plant material comes from legitimate conservation propagation programs
  • Be prepared for potential challenges, as rare plants often have very specific needs

Better Alternatives for Your Puerto Rican Garden

Instead of potentially contributing to the pressure on wild populations of this imperiled species, consider these more common Puerto Rican native alternatives that can give you that authentic island flora feeling:

  • Other native Cynanchum species that aren’t threatened
  • Native Puerto Rican milkweeds that support monarch butterflies
  • Hardy native vines and herbs suited to your specific growing conditions

How You Can Help

The best way to appreciate Mona Island swallow-wort might not be growing it in your garden, but supporting its conservation. Consider donating to botanical conservation efforts in Puerto Rico, or if you’re a serious plant enthusiast, connect with legitimate conservation organizations that might need volunteers for propagation or habitat restoration projects.

Remember, sometimes the most loving thing we can do for a rare plant is to admire it from afar while working to protect its wild habitat. After all, future generations deserve the chance to discover this remarkable little piece of Caribbean natural history too.

Mona Island Swallow-wort

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

Gentianales

Family

Asclepiadaceae Borkh. - Milkweed family

Genus

Cynanchum L. - swallow-wort

Species

Cynanchum monense (Britton) Alain - Mona Island swallow-wort

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