Sinningia helleri is the type species of the genus Sinningia, which means the genus is tied to this species. As long as the genus is recognized, it must include S. helleri. Therefore, to some extent, the definition of sinningia depends on the characteristics of S. helleri.
There's only one problem.
As far as anybody knows, S. helleri is extinct. It's not in cultivation. It can't be found in the wild. It's quite probable that it's gone, gone, gone.
In 2008 Dave Zaitlin provided me with an image via Google Books (thank you, Dave and Google!).
This picture is from The Gardeners’ Chronicle of June 1, 1907. The accompanying text says that the flowers are white with red calyces.
One noteworthy feature is how most of the flowers face one direction. Naturally the photograph was taken from that direction. This trait (flowerstalks bending toward the light) is shared with Sinningia guttata and S. lindleyi, both of which have mostly-white flowers.
Alain Chautems found this drawing of Sinningia helleri in Nees & Sinning 1831. That's Sinning (the person the genus Sinningia is named after), and Nees, brother of the one who defined the genus.
This plate clearly shows the keeled calyces enclosing the base of the flower, so reminiscent of S. guttata. The stout petioles are another point of similarity. One wonders whether the artist drew the flowers facing upward because that's what was there, or whether it was to show the details better; the flowers of S. guttata and S. lindleyi are held pretty much horizontally.
The leaves and flowers of S. helleri somewhat resemble S. guttata's, so I'm going out on a limb and guessing that S. helleri is (was) in the Sinningia clade, along with S. guttata and S. lindleyi.
White, ivory, or pale yellow flowers are not unknown outside the Sinningia clade (S. eumorpha and S. conspicua in the Dircaea clade, plus S. richii, S. barbata, and S. tubiflora in the Corytholoma clade).
Note the calyx description below, according to which the calyx is up to 2 inches long. That's a big calyx!
S. lindleyi and S. guttata have large, leafy calyces, but they aren't red, although those of S. lindleyi do have red markings (S. guttata's are green). At least, this is true of the plants in my possession. Also, do note the confusion between S. helleri and S. lindleyi in their original publications. So here is an alternative hypothesis: S. helleri would today be considered a form of S. lindleyi, and the reason it can't be found now is that any plants of it are taken to be S. lindleyi plants.
Just a thought. Wrong, no doubt, but still a thought.
Mauro Peixoto's Brazilian Plants site has a page about S. helleri, with a print.
I don't have access to the original publication of Sinningia helleri, but I found a description at the Factopia web site, according to which S. helleri has large red calyces (up to 2 inches [5 cm] long) and white corollas with red spots on a greenish throat. The leaves are 4-7 inches [10-17 cm] long and drooping. The (leaf) petioles, (flower) peduncles, stem, and leaf undersides are purplish. The stem is "a few inches high, thick, and slightly woody." (This also sounds close to S. lindleyi.)
This matches the Latin description I found at the Flora brasiliensis site. However, neither site (nor the print shown on Mauro's web site mentioned above) shows or says whether the plant has a tuber. This does leave us somewhat in the dark about the taxonomic position of this species.
One of the consequences of our not having a living plant of
Sinningia helleri is that it cannot be subjected to the DNA analysis that
Perret et al. did for the rest of the tribe.
So we don't know what its genetic relationships were.
It's possible that a herbarium specimen might have some DNA
Sinningia helleri was first published in 1825 by Nees.