North America Native Plant

Britton’s Dry Rock Moss

Botanical name: Grimmia brittoniae

USDA symbol: GRBR4

Habit: nonvascular

Native status: Native to North America  

Britton’s Dry Rock Moss: A Rare Native Treasure Worth Knowing Have you ever noticed tiny, dark cushions of what looks like miniature vegetation clinging to rocks in wild spaces? You might have encountered one of North America’s more elusive botanical residents. Meet Britton’s dry rock moss (Grimmia brittoniae), a small ...

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) ⚘

Britton’s Dry Rock Moss: A Rare Native Treasure Worth Knowing

Have you ever noticed tiny, dark cushions of what looks like miniature vegetation clinging to rocks in wild spaces? You might have encountered one of North America’s more elusive botanical residents. Meet Britton’s dry rock moss (Grimmia brittoniae), a small but remarkable native species that’s both fascinating and increasingly rare.

What Exactly Is Britton’s Dry Rock Moss?

Britton’s dry rock moss is a bryophyte – that’s the fancy scientific term for the group that includes mosses, liverworts, and hornworts. Unlike the flowering plants we typically think of when planning our gardens, this little moss is herbaceous and has a particular talent for making itself at home on solid surfaces like rocks and wood rather than nestling into soil.

This isn’t your typical lawn moss. Grimmia brittoniae forms small, dense cushions that attach directly to rock faces, creating what almost looks like nature’s own little throw pillows scattered across stone surfaces.

Where Does It Call Home?

As a native North American species, Britton’s dry rock moss has evolved to thrive in our continent’s unique conditions. However, the exact details of where you might encounter this moss remain somewhat mysterious, as its distribution isn’t fully documented in readily available sources.

A Species in Trouble

Here’s where things get serious: Britton’s dry rock moss carries a Global Conservation Status of S2, meaning it’s imperiled. This classification indicates extreme rarity, with typically only 6 to 20 known occurrences and somewhere between 1,000 to 3,000 individual plants remaining. That makes spotting one in the wild quite special – and quite concerning.

Spotting This Elusive Moss

If you’re lucky enough to encounter Britton’s dry rock moss during your outdoor adventures, here’s what to look for:

  • Small, cushion-like formations on rock surfaces
  • Dark green to blackish coloration
  • Dense, compact growth habit
  • Preference for dry rock environments
  • Attachment directly to stone rather than growing in soil

Is It Good for Gardens?

While mosses can add wonderful texture and ancient charm to naturalistic garden settings, Britton’s dry rock moss presents a unique situation. Given its imperiled status, this isn’t a species you should consider introducing to your landscape – even if you could find it for sale, which you almost certainly can’t.

Instead, if you encounter this moss in its natural habitat, the best thing you can do is:

  • Observe and appreciate it from a respectful distance
  • Avoid disturbing the area where it grows
  • Consider reporting your sighting to local botanical organizations
  • Help protect its habitat by following Leave No Trace principles

The Bottom Line

Britton’s dry rock moss represents one of those quiet conservation stories happening right under our noses. While it may not have the charismatic appeal of endangered mammals or birds, this little moss is fighting for survival in an increasingly developed world.

As native plant enthusiasts, our role with species like Grimmia brittoniae is less about cultivation and more about appreciation and protection. If you’re interested in incorporating moss-like textures into your garden, consider looking for more common native moss species that can be ethically sourced or naturally encouraged in appropriate garden conditions.

Sometimes the greatest gardening act is simply recognizing and protecting the rare treasures that already exist in wild spaces – even when they’re as small and unassuming as a cushion of moss on a rock.

Britton’s Dry Rock Moss

Classification

Group

Moss

Kingdom

Plantae - Plants

Subkingdom
Superdivision
Division

Bryophyta - Mosses

Subdivision

Musci

Class

Bryopsida - True mosses

Subclass

Bryidae

Order

Grimmiales

Family

Grimmiaceae Arn.

Genus

Grimmia Hedw. - grimmia dry rock moss

Species

Grimmia brittoniae R.S. Williams - Britton's dry rock moss

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