Can any one tell me about Nematanthus 'Petropolis'?
I believe it is a species. I got it at the San Francisco Gesnaiad Show a while back. I going to go out on a limb and say it came from Jon Dixon. :)
You got to the right place - let's wait for what Jon_D has to say.
I bought this cv. back around 1990 when the Gesneriad Research Foundation (Hans Wiehler and group) put out a little brochure with a small list of mail order plants, the only time they ever did this, alas. On that list were a number of new nematanthus species and hybrids. The other plants made it into general circulation (maculatus, crassifolius, 'Ubatuba', 'Sorocaba') but this one may have nearly disappeared. The hybrids in this group were all hybrids made by Hans in Sarasota, and named for his favorite cities in Brazil.
I forgot I had it, as the plant superficially is similar to hirtellus; and I was growing them outdoors, where they were growing kind of raggedly, covered with oak leaves and generally ignored. Then, a few years ago, I brought them all inside and realized I had two pots of hirtellus and one of 'Petropolis'. I was happy to see I still had this cv., which I had forgotten all about. So, I began propagating it. Last week I was discussing this one with Ingrid in Sweden who is now distributing it there, and she offered that it most likely is a cross of hirtellus and fluminensis, which I agreed. It has an upright habit with large yellow flowers with black maroon calyxes. Compared to hirtellus, the yellow corolla is much larger and showier. Its habit and foliage are close to hirtellus. It flowers over a long period, nearly all year in the greenhouse. Right now it is flowering very nicely.
To grow a nice plant, keep it pinched to force branching. Cuttings root easily, and the plant, like other nematanthus is cold tolerant down to about 30-32 degrees. Like other nematanthus it is an epiphyte, requiring the typical gesneriad mix. For best flowering give it bright shade.
Like hirtellus it has the interesting habit of budding up along the stem, often below the oldest leaves. Often a mature cutting will initiate buds after rooting and being potted up, making a striking small flowering starter plant. Last summer I took a bunch of rooted starts without flowers to the Norcal Cactus and Succulent show/sale. I put them out with a cut stem with flowers for an example. They all sold within the first two hours, and then someone talked me into selling them the cutting (which went back to France!). It isn't succulent but struck a cord.