Do these store well in vermiculite moistened with a few drops of water over the winter, or do I need to maintain viable rhizomes some other way?

I am green from envy. What a cool plant! I saw it at the Gesneriad convention - and loved it.

I think your method is the best. I use a little sprinkle of Captan to keep fungus at bay and keep and eye on rhizomes so they won't go dry.

Irina

Gloxinia nematanthodes is now Seemannia nematanthodes. This is a great species that I've grown for several years, both in the ground and in containers. It has a very long blooming period and has held up well to summer heat and humidity. They do best with some direct sun during the day, but appreciate mid-day shade.

I keep Seemannia (and Achimenes) rhizomes bone-dry over the winter, usually stored in a small amount of dry potting mix. As long as you keep them cool and dry they will stay dormant for several months. If you give them any moisture at all, you risk (a) rot or mold and (b) premature sprouting. They will eventually start sprouting regardless of what you do, but even then they will be okay for a few more weeks. I usually start them under lights indoors in early spring and put them out once the weather has warmed up a bit (usually early May).

Here are a couple of photos of S. nematanthodes growing in a couple of different places:

In our very dry climate - I keep an eye on the baggies with rhizomes and add 1-2 drops of water every so often - otherwise they dry to crisp. Achimenes though keeps the best in last year pots.

On the other side - if something starts sending shoots - I just pot it - no way I can grow gesneriads outside anyway - so I do not need to time them to the spring.

Irina