North America Native Plant

Small’s Acroporium Moss

Botanical name: Acroporium smallii

USDA symbol: ACSM3

Habit: nonvascular

Native status: Native to North America  

Synonyms: Sematophyllum smallii R.S. Williams (SESM4)   

Small’s Acroporium Moss: A Rare Native Bryophyte Worth Protecting If you’ve ever wondered about the tiny green carpets that quietly adorn rocks, logs, and forest floors, you’ve likely encountered the fascinating world of mosses. Today, we’re spotlighting one of North America’s rarest mosses: Small’s acroporium moss (Acroporium smallii), a critically ...

Rare plant alert!

Region: Conservation status by state

Status: S1?: Status is uncertain but is somewhere between the following rankings: Inexact rank: ⚘ Critically Imperiled: Extremely rare due to factor(s) making it especially vulnerable to extinction. Typically 5 or fewer occurrences or very few remaining individuals (<1,000) ⚘

Small’s Acroporium Moss: A Rare Native Bryophyte Worth Protecting

If you’ve ever wondered about the tiny green carpets that quietly adorn rocks, logs, and forest floors, you’ve likely encountered the fascinating world of mosses. Today, we’re spotlighting one of North America’s rarest mosses: Small’s acroporium moss (Acroporium smallii), a critically endangered bryophyte that deserves our attention and protection.

What Exactly is Small’s Acroporium Moss?

Small’s acroporium moss is a native North American bryophyte – that’s the fancy scientific term for the group that includes mosses, liverworts, and hornworts. Like all mosses, this species is herbaceous and typically grows attached to solid surfaces like rocks, fallen logs, or tree bark rather than directly in soil. You might also see it referenced by its scientific synonym, Sematophyllum smallii.

As a bryophyte, this moss lacks the root systems, stems, and leaves we associate with typical garden plants. Instead, it forms small, intricate structures that help it absorb moisture and nutrients directly from its environment.

Why This Moss Matters (And Why It’s So Hard to Find)

Here’s where things get serious: Small’s acroporium moss has a Global Conservation Status of S1?, meaning it’s critically imperiled. This designation indicates extreme rarity, with typically fewer than five known occurrences and fewer than 1,000 remaining individuals. In the plant world, this is about as rare as it gets.

The exact geographical distribution of this moss remains unknown, which speaks to just how uncommon encounters with this species are. Its rarity makes it a species of significant conservation concern.

Should You Try to Grow Small’s Acroporium Moss?

Given its critically imperiled status, we strongly recommend against attempting to collect or cultivate Small’s acroporium moss. Here’s why:

  • Its extreme rarity means every individual matters for species survival
  • Collecting from wild populations could further threaten the species
  • No cultivation methods are documented for this species
  • Growing conditions and care requirements are unknown

How to Identify Small’s Acroporium Moss

While we don’t have detailed morphological descriptions readily available, if you encounter what you believe might be this rare moss, consider yourself incredibly fortunate. As a bryophyte, it will:

  • Appear as small, green formations on rocks, logs, or bark
  • Lack true roots, stems, and leaves
  • Feel soft and spongy when moist
  • Form intricate, tiny structures visible under magnification

If you suspect you’ve found this species, photograph it (without disturbing it) and contact local botanical experts or conservation organizations.

Supporting Moss Conservation in Your Garden

While you shouldn’t attempt to grow Small’s acroporium moss, you can create moss-friendly conditions that support other native bryophyte species:

  • Maintain shaded, moist areas in your landscape
  • Leave fallen logs and rocks undisturbed
  • Avoid using fungicides or herbicides that might harm moss communities
  • Create habitat diversity with varying moisture levels

The Bigger Picture

Small’s acroporium moss reminds us that native plant conservation isn’t just about showy wildflowers and majestic trees. Sometimes the most important species are the tiniest ones – the mosses, lichens, and other often-overlooked organisms that form the foundation of healthy ecosystems.

While we can’t recommend growing this critically imperiled species, learning about it helps us appreciate the incredible diversity of native plants and the importance of protecting even the smallest members of our natural communities.

Small’s Acroporium Moss

Classification

Group

Moss

Kingdom

Plantae - Plants

Subkingdom
Superdivision
Division

Bryophyta - Mosses

Subdivision

Musci

Class

Bryopsida - True mosses

Subclass

Bryidae

Order

Hypnales

Family

Sematophyllaceae Broth.

Genus

Acroporium Mitt. - acroporium moss

Species

Acroporium smallii (R.S. Williams) H.A. Crum & L.E. Anderson - Small's acroporium moss

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