Recently on the gesneriphile list there have been some very, very interesting posts about propagation of various gesneriads using only leaves. Not the stems or part of a tuber or rhizome, but just the leaf portion of things. One of the regular and very knowledgeable contributors to the gesneriphile list at... firstname.lastname@example.org wrote something that was so excellent it had to be shared! Jon Dixon wrote:
Some gesneriads propagate better from leaves than others. Many of the plants we regularly prop from leaves are old world--such as streps, chiritas, AV's, and petrocosmeas. Even aeschynanthus will propagate from leaves. With the latter, leaves are much more difficult and slower than cuttings, but will work. Some years ago I did a few experiments and concluded that aeschynanthus leaves root and sprout best when grown in a favorable media, enclosed, under lights, and fed. I have used perlite/vermiculite or long fiber sphagnum moss. When leaves are grown under less ideal conditions, such as out in the open, the rooted leaves often sit for a year or more before decaying. Often, in these kinds of nutrient poor media, the leaves will sit if not lightly fertilized. The same rules seem to apply to other gesneriad leaves that are more difficult, such as episcias.
Once I had very good luck getting sprouts when I rooted the small leaves of Aeschynanthus lanceolatus in P/V laid down about an inch thick in a sweater box and under lights. The size of the container provided just the right degree of high humidity without dripping condensation. The same methodology also produced the best sprouting from 2" long strep leaf wedges.
Many of our new world gesneriads will not root from leaves, or only rarely, such as columnea, nematanthus, and codonanthe. But, nautilocalyx propagate readily from leaves. This genus is closely related to episcia, yet episcias sprout poorly from leaves while nautilocalyx sprout fairly quickly. a third related genus, paradrymonia also root well from leaves, but alsobia has been a total failure. Gasteranthus will also grow well from leaves.
Sinningias are a mixed bag. Some propagate from leaves and others do not. Sometimes, on the same species, new young leaves will root, but older leaves taken after the stem has flowered will not. Once I used my above method on a large sinn. leaf from a species that had already flowered--I am not sure; but, I think it was iarae. I enclosed the large leaf in a large ziplock bag over a pot and put it at the back of my light stand. About a year later I decided to open the bag and see how things were going. The leaf was still healthy, but there were no signs of roots. So, I tossed it--a year is long enough to make roots, I think. Previously I had once taken a leaf from a large growing S. reitzii hybrid. It also sat enclosed in its ziplock wonderland for over a year before I ventured a peek. What I found was the healthy leaf connected to a cube shaped tuber that filled the 2" pot. There was no sign of a sprout, but I potted it up, fed it, and was rewarded with growth.
Of all the sinningia species, speciosa is the propagating fool. You can get new plants from just about any part of the plant--stem, tuber, seed, leaf, and pedicel. The latter was demonstrated by someone here on gesneriphiles. I never had luck, but didn't give my cuttings all of the above conditions. It was reported that fresh pedicels from corollas that had just withered but were not pollinated, cut at the base (but with no stem or bud tissue) and with the fleshy calyx lobes, rooted and produced tubers. I think the attached calyx lobes acted like succulent leaves, enabling rooting. Many of us remember the work that Marty Mines did in the 80's, propagating mini sinningias from tissue culture. He demonstrated that this was a preferable method for mass production of named hybrids that did not come true from seed. I can't remember if he used cut sections of pedicels or leaves.
Another friend of mine, a succulent grower, demonstrated that tissue culture can be done without especially sterile conditions. He propagated haworthias using sterile media but did not need a glove box or a flow hood. He did all his prep work at a desk, with an aquarium sitting on its side, using spray bottles of bleach or alcohol to spray down everything. He had the same percentage of contamination as those doing the same work under a hood (less than 25%, mol). His method was written up in an issue of the Cactus and Succulent journal sometime in the mid 90's, mol.
Patrick Worley used to regularly propagate his new rhizomatous hybrids from leaves. He seemed to have great success using just leaves. Sometimes they produced rhizomes and sometimes they sprouted new shoots. A terminal leaf cutting taken when the plant is getting ready to flower and cut with a bit of the stem and bud may produce flowers before anything else. He also mass produced his new hybrids by breaking up rhizomes into individual scales and then sowing them like seeds on sterile media, enclosed and under lights. I believe he used sweater boxes.
With any propagation, the time of year is important. For example, I have been able to root stem cuttings of columneas or episcias in water during summer time, but have had no luck in winter. Both times the cuttings were in vases of water on bright windowsills.
Regarding streptocarpella, which Gene was unsuccessful with--many years ago a late member of the SF Gesneriad society, Chet Nave, brought in sprouted leaves of 'Concord Blue', that were done in a small pot of P/V enclosed in a plastic bag in his greenhouse. I suspect that he did this in the warm season, although living near the ocean in Pacifica, there is really no warm season. Reminded of Chet's success and knowing that aeschynanthus leaves root, I did an experiment with closely related Lysionotis pauciflorus leaves. I had no success but need to try this experiment again, making sure that I give the cuttings ideal conditions, and doing it in summer.
I am sure experimentation will yield some surprising discoveries that while not necessarily productive are nevertheless educational.Thanks to Jon Dixon for letting us share his thoughts!