Very nice image of this Lycopodium. It would be a difficult subject for a terrarium. However, it could be done if your terrarium was a cold terrarium with lows falling into the 30s and the highs probably into the mid 60s (all Fahrenheit). The other barrier to effective cultivation would be having enough of the rhizomes (roots) of the plant to help it survive. It may occur in your state. If you know anyone who owns forested land that has populations of this club moss on it then I would recommend that you get permission to pull a plug of a patch of the plant. Be sure to note the environmental situation and find out about the amount of light, rainfall, seasonal temperature changes as well as rainfall cycles. I would keep the terrarium outside in shade on the north side where it would be the coolest. Be careful with the humidity level as fungus could develop and overtake the plant.
I have had limited success with different species of this genus. Mostly due to the simple fact that I have not had the time needed to really study and monitor the plants as should be done for this part of California. My own problems center around on keeping the plants cool enough!
Otherwise I think that they would do well here. One important consideration is that they do not seem to enjoy having their roots disturbed either but I have not really done much in the way of experimenting with them on this issue.
There are two sources of Lycopodium species. One is Orchid Gardens, 2232 139th Ave. N.W., Andover, Minnesota 55304
Mr. Phillips sells a 3 species collection of L. annotinum, L. clavatum, and L. obscurum (the easiest grower of the three) for only $6 USD. You will have to write him for a copy of a catalog. Send along a dollar for it.
There is one other source of a native Lycopodium species,
I think it is Lycopdiella inundata. It can be purchased over the net. Check the link below. Of all the species of
Lycopodium and related genera (most of whom had been included in Lycopodium in the past) the Lycopodiellas are perhaps the easiest to grow. It is a bog type plant and just needs quality water, distilled or r/o, and an acidic mix, such as a blend of river sand and peat moss. It can handle some flooding and very mucky conditions.
To expand upon your interest there is a gentleman in Florida who sells tropical species of Lycopodium.
Rare Flora-click here I think this is it.
Availabiltiy is variable and on a first come basis.

And if you find Lycopodium intersting you might want to explore the world of our native Tetragonostachys section of Selaginella. These are the moss like species and occur mostly in the western half of the country though around 3 species are prevalent in the eastern half, Selaginella rupestris being the most commonly encountered one. Check my site for info and links to images and other relevant information.
Selaginella-click here
These plants are much easier to grow and are very interesting plants as well.
You might be interested to know that a subspecies of L. clavatum occurs in the southern area of Africa!

Here is a link that might be useful: Lycopodiella for sale here

I need to fix the link above to Selaginella. The topcities site dumped my pages. Here is the web journals at Photobucket:
Selaginella journals

Here is the link here at GardenWeb to images of what I could find of the North American species.
Selaginella links

I need to fix the link above to Selaginella. The topcities site dumped my pages. Here is the web journals at Photobucket:
Selaginella journals

Here is the link here at GardenWeb to images of what I could find of the North American species.
Selaginella links

This is WAY too coarse for a terrarium. The only native Lycopodiums that might be suitable for a terrarium might be Lycopodiella inundata or Dendrolycopodium obscurum (and maybe dendroideum). However, try native Selaginella -- Selaginella apoda or eclipes, either one, makes a GREAT terrarium subject.

Hey John, it really depends on how large the terrarium is!! All lycopodiums are best pot grown or mounted for the epiphytic species. S. apoda is one tough plant and resows from spores quite easily. S. apoda is available in the trade.

Google for it.

Oh, I grow it. Also S. eclipes and S. densa, and I expect to have S. rupestris and S. wallacei in the spring. I also grow Lycopodiella inundata, L. alopecuroides, and Diphasiastrum digitatum. I plan to start growing Lycopodium clavatum, Dendrolycopodium obscurum, and D. dendroideum this spring. I am also growing Equisetum arvense, E. variegatum, E. hyemale var. affine, E. scirpoides, and E. sylvaticum, and expect to add E. myriochaetum, E. diffusum, E. fluviatile, E. palustre, E. laevigatum, and E. pratense this coming year.

Considering covering part of the wall of my office in Japan with this Foxtail [狐のしっぽ / ヒゲノカズラ]--as my coworkers call it--Lycopodium clavatum, I believe. It grows rampant throughout the pine forest outside of our school. I thought it might be a good low-light plant to add some color to the typical, drab Japanese school office (which I have been slowly transforming and I am lucky to share with a very flexible coworker). I tacked some milk cartons with typical potting soil in them to the wall and immersed the rhizomes in the soil for a quick test run. Perhaps I'll spraypaint the milk cartons one or two colors if things work out.

What do you guys think? Will I have success with something like this? With typical potting soil? Windows are west-facing and don't get lots of direct sunlight (like the forest where I find the Foxtail Clubmoss). Office is not air-conditioned in the summer (meaning it nearly mirrors outside temps/humidity).