I should probably add that at least one Cryptocoryne species (aroid) can be reproduced from a leaf cutting. The species escapes me at the moment, but it has been reported in the European literature and the same species has done so for me and for my friend and neighbor Chris Newell. I have tried several others without success.
The technique I used was to simply take a leaf and lay it and its petiole on an organic-rich substrate (wet, of course, since Crypts are aquatic or semi-aquatic), and partly cover the leaf edges with additional substrate. (I did not use any rooting hormone, but maybe that would help.) Then wait. And wait. Many months later I found an offset coming from the leaf portion. No bulblets. Just right off the leaf edge.
As I said, several other attempts with other clones and species were not successful for me. When it fails the exposed parts of the leaf just turn to mush. In my successful try the leaf stayed firm and green the whole time.
It would be fascinating to know if there is a physiological reason that allows this to happen. Perhaps a careful catalogue of species that can be so reproduced and those which cannot would differentiate a parting evolutionary pathway.
For any of you with access to Crypts in the wild (Peter?), next time please poke around a little and see if any rooting from leaves can be detected in a wild population.
I'll see if I can dig out the species ID from my notes. Don't hold your breath, though; it's been a while.
I have not done it myself, but, Peter Boyce told me that certain clumping species of Schismatoglottis can be propagated by leaf cuttings. I have no idea if this extends to the whole genus, but, perhaps Peter will respond. This conversation arose due to the habit of certain Schismatoglottis that pup and the mother plant dies. While I am on this forum, I'd love to see more species of Schismatoglottis in cultivation. It is like Philodendron and Anthurium...large genera, but relatively few species in cultivation. Unfortunately, this is not likely to change in the near future.
We detailed our research on rooting amorphophallus from leaf cuttings in an article published in Aroideana, Volume 30, 2007. Pinellia can also be rooted, as can some tropical arisaema.
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I am again doing some digging as a result of an ongoing discussion with a group of growers. It is the opinion of some that aroids can be induced to generate a totally new plant by placing growth hormone on the petiole of a leaf. I have read all I can find and do not believe this information to be accurate.
From the text of The Genera of Araceae it appears the only two aroids that are capable of the regeneration of a new plant from a leaf are Zamioculcas zamiifolia and Gonotapus boivinii. This unique ability is the result of a bulblet being formed at the juncture of the blade and the petiole and appears to happen as a survival form during hostile seasons of the year. From TGOA: "Regeneration of tubers, leaves and roots from leaf segments is well known in Zamioculcas zamiifolia and Gonotapus boivinii (Engler 1881, Schubert 1913, Cutter 1962). Isolated entire leaflets of Zamioculcas and Gonotapus spontaneously develop a basal swelling, followed by the formation of roots and up to 3 buds, over a 6-9 week period for Zamioculcas. Leaf regeneration in Gonotapus is more rapid. The results of experimental manipulation of isolated leaflets grown in culture show that any part of the compound leaf is capable of regeneration".
One gentleman appears to be insisting any of the other four Gonotapus species is capable of the same thing. I have read and reread the section in TGOA on this subject and there is a mention of a few other aroids that produce bulblets at the juncture of the leaf and petiole but other Gonotapus are not mentioned. More from TGOA:
"Leaf tubercles and regeneration. Tubercles regularly develop at the juncture of leaflet and petiole in Pinellia fernata (Hansen 1881, Linsbauer 1934, Troll 1939) at the apical end of petiole in Typhonium bulbiferum (Sriboonma et al. 1994) and at the first and second order divisions of the leaf of Amorphophallus bulbifer (Troll 1939). Tubercles in Pinella may also form spontaneously along the petioles or can be induced at the basal part by cutting into segments (Linsbauer 1934) Tubercles may develop in Typhonium violifolium at the leaf apex, pale apex and the apex of this sheath (sriboonma et al, 1994)." Do any of the other four species of Gonotapus actually do leaf regeneration? And if not, can any of our scientists give me a source of documentation as to why leaf regeneration does not happen in aroids? If any grower has obsserved this behavior, can you document it?
I am not trying to "win an argument, I just want to make sure I understand this growth form as it relates to aroids.