Thompson’s Rockcress: A Rare Pacific Northwest Gem Worth Protecting
Meet Thompson’s rockcress (Arabis microphylla var. thompsonii), a botanical treasure that’s as rare as it is intriguing. This little-known native plant represents one of nature’s more exclusive offerings – a perennial forb that calls the Pacific Northwest home but exists in such limited numbers that most gardeners will never encounter it in the wild, let alone in cultivation.
What Makes Thompson’s Rockcress Special
Thompson’s rockcress belongs to the mustard family and grows as what botanists call a forb – essentially a soft-stemmed perennial that lacks the woody tissue of shrubs and trees. Unlike its showier garden cousins, this plant has evolved to thrive in very specific conditions found only in Washington state, making it a true regional endemic.
As a perennial, Thompson’s rockcress returns year after year, developing its root system and slowly establishing itself in suitable habitat. Its growth habit reflects the challenging environments where it naturally occurs, growing close to the ground and maintaining a low profile.
A Plant on the Edge: Understanding Its Rarity
Here’s where things get serious: Thompson’s rockcress carries a Global Conservation Status of S5T1Q, which indicates this variety is critically rare. The T1 ranking means it’s among the most imperiled plant varieties, with very few known populations and a high risk of extinction. This isn’t a plant you’ll find at your local nursery, and there’s a very good reason for that.
Important Conservation Note: Due to its extremely rare status, Thompson’s rockcress should only be grown using responsibly sourced material, and even then, only as part of legitimate conservation efforts. Wild collection is absolutely not appropriate and could harm the few remaining populations.
Where Thompson’s Rockcress Lives
This remarkable plant is found exclusively in Washington state, where it occupies very specialized habitats. Its limited geographic range makes it particularly vulnerable to habitat loss and environmental changes. The fact that it hasn’t spread beyond Washington’s borders suggests it has very specific growing requirements that aren’t easily replicated elsewhere.
Should You Grow Thompson’s Rockcress?
The short answer is: probably not, and here’s why. Thompson’s rockcress represents one of those plants that’s better appreciated from afar and protected in its natural habitat rather than brought into cultivation. Its critical rarity status means that:
- Seeds or plants are extremely difficult (and potentially illegal) to obtain
- Its specific growing requirements are poorly understood
- Conservation efforts are better focused on protecting existing wild populations
- There are many other native Washington plants that offer similar ecological benefits without the conservation concerns
Better Alternatives for Your Garden
If you’re drawn to the idea of growing native rockcresses in your Pacific Northwest garden, consider these more widely available alternatives:
- Lyall’s rockcress (Arabis lyallii) – another Washington native that’s more common
- Holboell’s rockcress (Arabis holboellii) – found throughout the western states
- Other native mustard family plants that provide similar ecological functions
Supporting Conservation
The best way to grow Thompson’s rockcress is to support conservation organizations working to protect Washington’s native plant communities. Consider contributing to habitat preservation efforts, participating in citizen science projects, or volunteering with local native plant societies.
Sometimes the most responsible thing we can do as gardeners is to admire rare plants from a distance while focusing our cultivation efforts on species that can thrive in our gardens without compromising wild populations. Thompson’s rockcress serves as a reminder that not every plant is meant for every garden – and that’s perfectly okay.
The Takeaway
Thompson’s rockcress stands as a testament to the incredible diversity of Pacific Northwest flora and the importance of protecting rare species. While you probably won’t be adding this particular plant to your garden wishlist, knowing about it helps us appreciate the complex web of native plants that make Washington’s ecosystems so special. Every rare plant like Thompson’s rockcress represents millions of years of evolution and adaptation – a living piece of natural history worth protecting for future generations.
