Those of you who don't have room for more indoor plants will be happy to hear that there is one ever-bloomer which can remain happy in a 3-inch pot for years. The Mexican foxglove (Tetranema roseum or mexicana)—sometimes also known as Mexican violet--does, indeed, hail from Mexico, but doesn't come close to matching the towering size of genuine foxgloves.
Once called Allophyton mexicanum and growing only 6 to 12 inches tall, tetranema can flower in the shade as foxgloves and violets often do, preferring bright, indirect light or partial sun rather than direct sunlight. It is hardy in USDA zones 10 and higher, and reportedly vigorous enough to take over lawns in such climates. Elsewhere, it must be grown indoors.
Its short stature makes it an ideal plant to place under a fluorescent grow light, along with gesneriads such as African violets. There, it will bloom off and on for much of the year--most heavily during summer--producing clusters of ten to twenty 1/2-inch long tubular, rose-tinged lavender flowers with whiter spots on their lower lips. The cultivar 'Album' makes white flowers instead. Tetranema translates to "four filaments" in reference to each flower's four stamens.
The rosette of oval "quilted" leaves somewhat resembles the foliage of a primrose, but those leaves are glossier and more pointed than those of most primulas. Although tetranema sometimes is recommended for terrariums, keep in mind that the plant enjoys high humidity and lightly damp soil, but is averse to soggy conditions. So, if you have a tendency to overwater, you might want to keep it in a terracotta pot filled with fast-draining cactus potting soil.
Should you want it to continue to bloom during the winter, place it in a location where the temperature never falls below 60 degrees Fahrenheit. Although tetranema is perennial, older specimens reportedly have a tendency to die off suddenly and younger ones bloom better, so it's a good idea to allow the plant to make a few offsets.
The seed can be difficult to find, but apparently not difficult to germinate. Simply press it into the surface of damp and sterile seed-sowing mix, keep that mix at room temperature (around 70 degrees F.), and the seeds may begin to sprout as early as three days later. A seedling reportedly can bloom during its first summer, if started early in the year.
There actually are seven species in the Tetranema genus, but roseum apparently is the only one available to gardeners, though I was able to find images of the recently "discovered" T. gamboanum and T. floribundum as well. Native to Costa Rica, they both have tubular red flowers of the sort which appeal to hummingbirds.
I'm guessing they would be even more difficult to acquire than the lavender type, though. Having seen only a single U.S. greenhouse which actually sells Tetranema roseum plants, I've posted a want for them on a seed exchange site. I'm hoping that one of those Florida gardeners who might have a lawn full of them can harvest some seeds for me!
Photos: The banner photo is by Tony Rodd and the other two photos by Maja Dumat, all courtesy of Flickr Creative Commons and this license. The antique image is from M. E. Eaton's Addisonia, Volume 11, courtesy of plantillustrations.org.