I get very excited when I am able to identify a new moss. This is mainly due to the fact that moss ID is one of my weakest points. I was sitting down on a rock the other day taking a break from vegetation surveys when I looked to my right and saw something peculiar. The area was pretty sloped and there was some exposed soil in the vicinity. Covering some of that soil was what looked like green fuzz. Embedded in that fuzz were these strange green urns.
I busted out my hand lens and got a closer look. This was definitely a moss but one I had never seen before. The urns turned out to be capsules. Later, a bit of searching revealed this to be a species of moss in the genus Diphyscium. This genus is the largest within the family Diphysciaceae and here in North America, we have two representatives - D. foliosum and D. mucronifolium.
These peculiar mosses have earned themselves the common name 'powder gun moss.' The reason for this lies in those strange sessile capsules. Unlike other mosses that send their capsules up on long, hair-like seta in order to disperse their spores on the faintest of breezes, the Diphyscium capsules remain close to the ground. In lieu of wind, a powder gun moss uses rain. In much the same way puffball mushrooms harness the pounding of raindrops, so too do the capsules of the powder gun moss. Each raindrop that hits a capsule releases a cloud of spores that are ejected into an already humid environment full of germination potential.
Luckily for moss lovers like myself, the two species of Diphyscium here in North America tend to enjoy very different habitats. This makes a positive ID much more likely. D. foliosum prefers to grow on bare soils whereas D. mucronifolium prefers humid rock surfaces. Because of this distinction, I am quite certain the species I encountered is D. foliosum. And what a pleasant encounter it was. Like I said, it isn't often I accurately ID a moss so this genus now holds a special place in my mind.