Among Japan's amazing diversity of plants that can overwhelm a visitor from overseas, there are (thankfully) some familiar forms. Astonishingly, given the literally hundreds of thousands of plant species on Earth, some here will be familiar whether you hail from North or South America, from Europe, Africa, elsewhere in Asia or even the Antipodes.

I am thinking in particular of the club mosses. These apparently mosslike plants send runners along the surface of the ground that look like miniature conifer branches -- hence another common name for the various club mosses is ground-pines.

These species belong to the genus Lycopodiaceae, which is also known as the genus Lycopodium -- a name derived from the Greek words lykos (wolf) and podos (foot), giving them the common name of "wolf's paw."

However, you may be familiar with Lycopodium from a very different perspective -- if you are an explosives expert, that is. The name is also a term used for a fine powder, consisting of the dustlike spores of the plant, which is so highly flammable that it is sometimes used in the making of fireworks.

In fact, the expression "flash in the pan" probably derives from the use of Lycopodium spores placed on a heated metal tray as a flash powder in early photography.

When you're out and about, though, there's no need to worry about the wild plant, as this is low-growing, creeping and lacking flowers -- and not at all explosive.

The Lycopodiaceae are a primitive group of plants that were extremely successful in the distant past -- we all know them, though, in a quite different form.

This is because they were the dominant plant group during the Carboniferous Period more than 300 million years ago, when they towered to the size of trees. So common and large were they during that time that they form the bulk of the coal deposits we burn today.

Nowadays, descendents of those early species can still be found in just about every region of the world. Hence, wherever you hail from, you may find them familiar -- though they are now so diminutive you might just tread on one without realizing.

Despite commonly being called club moss, Lycopodium species are more closely related to ferns. Mostly found in temperate regions of the globe, they appear to favor mixed hardwood forests, but they can also be found where conifers and hardwoods are growing together.

Although they occur in a wide range of habitats, many of the species prefer cool, moist conditions like the one pictured here, that was growing on a very light soil overlying volcanic tephra on Mount Komagatake in Hokkaido.

The ground-hugging rhizomes snaking their way across the ground are lateral branches that allow the plant to traverse areas of poor or hard-packed soil and to straddle rocky and wet areas as they snake off in search of better conditions elsewhere. From these branches, roots grow down to anchor the plant in the surface soil and absorb water and nutrients.

For these plants, having aerial stems serves a double purpose: They can photosynthesize to produce energy that is stored in the rhizomes for future use, and they produce spores. Lycopodium species are evergreens, which gives them an additional window of opportunity -- literally. In deciduous forests there are periods in both spring and autumn when the trees lack leaves, and during those periods, an evergreen plant on the forest floor can take advantage of the additional light resources that come as an early and late bonus.

Despite this twice-yearly energy-absorption bonus, though, it still takes the aerial stems 4 to 6 years to reach maturity, and only then do they produce their upstanding strobili, whose resemblance to raised clubs is what gave this group of plants its name.

The conelike strobili harbor specialized leaves, called sporophylls, that produce the spores that allow Lycopodium species to reproduce sexually. Like ferns, they take two generations to reach maturity. After germinating in the surface layer of the soil, the spores form what is known as a gametophyte. Genetic recombination then takes place between gametophytes, and finally a new individual sporophyte begins to grow.

As the new plant develops, it relies on vegetative reproduction to expand its area of cover, which it does by sending out its own rhizomes across the surface.

This cycle can take as many as 20 years to complete -- not so long, you may think, but in some parts of the world these plants are harvested with little thought for how long they have taken to mature.

In the United States, Lycopodium is classified as a "nontimber" or "special forest product" that may be collected for various uses, including in the floral industry for winter decorations, and for use in medicinal and homeopathic remedies.

Lycopodium has long been used to help stop bleeding, and today it is still used by herbalists to treat minor skin wounds. When I checked its homeopathic uses, I found that it was listed for hundreds of conditions -- making it hardly surprising that it is often collected.

But we're not just talking about casual collection because, in the mid-1990s, researchers found that just two buyers in Wisconsin and the Upper Peninsula of Michigan were handling approximately 85 tons of the stuff a year!

So the next time that you might be tempted to pull up some Lycopodium, give a thought to the fact that it may have taken more than 20 years to reach the size of the one shown here . . . and its venerable ancestors are still fueling coal-burning power stations around the world.