Supine Bean: A Rare Native Legume Worth Protecting
Meet the supine bean (Macroptilium supinum), one of Arizona’s most elusive native plants. This little-known perennial legume is so rare that most gardeners have never heard of it—and for good reason. With fewer than 20 known populations in the wild, this herbaceous beauty is fighting for survival in its native Arizona landscape.
What Makes Supine Bean Special?
The supine bean belongs to the legume family, which means it has the superpower of fixing nitrogen in the soil—a trait that makes it valuable both ecologically and horticulturally. As a perennial forb, it lacks woody stems but returns year after year from its underground root system. You might also see it listed under its scientific synonym, Phaseolus supinus, in older botanical references.
Where Does Supine Bean Call Home?
This native plant is exclusive to Arizona within the United States, making it a true regional treasure. Its extremely limited distribution contributes to its imperiled conservation status—scientists classify it as S2, meaning it’s vulnerable to extinction due to its rarity.
The Rarity Reality Check
Here’s where things get serious: supine bean is considered imperiled, with only 6 to 20 known occurrences remaining in the wild. This conservation status means that while we’d love to encourage native plant gardening, this particular species requires extra consideration.
If you’re interested in growing supine bean:
- Only obtain plants or seeds from reputable native plant societies or conservation organizations
- Never collect from wild populations
- Consider it a conservation effort rather than just garden decoration
- Contact local botanical gardens or universities about conservation programs
Growing Conditions and Care
Unfortunately, detailed growing information for supine bean is as rare as the plant itself. However, as an Arizona native and member of the legume family, it likely prefers:
- Well-draining soils typical of Arizona’s arid regions
- Full to partial sun exposure
- Minimal water once established (drought tolerance is common among Arizona natives)
- Hot, dry summers and mild winters
Why Consider This Rare Beauty?
Growing supine bean isn’t just about adding another plant to your garden—it’s about participating in conservation. As a nitrogen-fixing legume, it can improve soil health while supporting Arizona’s native ecosystem. However, the responsibility that comes with growing such a rare species isn’t for every gardener.
Alternative Native Legumes
If you’re drawn to the idea of native Arizona legumes but want something more readily available, consider these alternatives:
- Desert broom (though not a legume, it’s a hardy Arizona native)
- Other Macroptilium species that may be more common
- Native Phaseolus species with better availability
The Bottom Line
Supine bean represents the fascinating but fragile world of rare native plants. While its conservation status makes it challenging for typical home gardening, it serves as an important reminder of Arizona’s unique botanical heritage. If you do have the opportunity to grow this rare gem, treat it as both a garden plant and a conservation effort—future generations of both plants and plant lovers will thank you.
Remember: sometimes the most beautiful garden contribution we can make is helping preserve species that might otherwise disappear from our landscapes forever.
