Plagiomnium cuspidatum

Plagiomnium cuspidatum (commonly known as Woodsy Star Moss or Cuspidate Mnium Moss) is a widespread species of moss from the family Mniaceae. It thrives across temperate to subtropical regions—on forest floors, by streams, on moist meadows, soil slopes, and in humus-rich environments. Here’s a closer look at its key traits and care tips:

Morphological Features

• Leaves:

  
  

  The leaves are elongated-oval with a distinctly sharp tip (hence the name “cuspidate”), finely serrated edges, with prominent veins and a vibrant green to deep green hue.

• Growth Habit:

  
  

  Its stems creep or stand slightly upright, forming dense, lush mats of green.

• Height:

  
  

  Typically grows 2–8 cm tall, classifying it as a small- to medium-sized moss.

• Texture:

  
  

  Soft and pliable when wet, the leaves curl slightly when dry.

Habitat Preferences

• Thrives in moist, semi-shaded to shaded areas, tolerating occasional bursts of direct sunlight.

• Soil: Not demanding, as long as the substrate stays damp.

• Needs high humidity, spreading rapidly under the right conditions to form expansive mats.

Why It’s Special

Here’s the highlight: Plagiomnium cuspidatum can survive underwater.

Although it normally grows above water, when water levels rise and submerge its habitat, it continues to thrive—while other mosses perish. It transitions seamlessly between two states:

• In low water, it spreads as a lush ground moss.

• When submerged, it behaves like aquatic vegetation, functioning much like underwater plants.

This adaptability makes it ideal for stream banks, waterways, or areas with fluctuating water levels. When dry, it’s moss. When submerged, it transforms into aquatic greenery.

Using It in Moss Terrariums

If certain parts of your terrarium regularly flood or hold standing water, Plagiomnium cuspidatum is your best choice. Lay down a patch in those wet zones, and it will thrive where most mosses struggle.

Check out the photos below:

Originally, the terrarium was planted with Hypnum plumaeforme moss. I didn’t intentionally introduce Plagiomnium cuspidatum. But after leaving the setup in someone else’s care during a trip, they overwatered, and large areas became submerged.

Now, notice how Plagiomnium cuspidatum has emerged and started taking over. If this continues, soon Hypnum plumaeforme moss will vanish entirely.

In the wild (at least where I live), these two mosses often grow together. But they balance differently: Hypnum plumaeforme is more drought-tolerant, while Plagiomnium cuspidatum dominates when water becomes excessive.

In my latest terrarium builds, I’ve been using Plagiomnium cuspidatum extensively, so I thought it deserved a proper introduction here.

This blog post will be regularly updated as I experiment and share more observations about this versatile, amphibious moss.