Maybe someday Colocasia and Alocasia will become one genus... the difference is only in number of ovules in a female flower (I don't know what about cytology).
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To: Discussion of aroids
Sent: Tuesday, January 24, 2006 1:16 PM
Subject: Re: [Aroid-l] Intrageneric crossing - a good reference
Peter:Your note is quite interesting about the possible mis-classification of Colocasia gigantea. I have always found it unusual that C. gigantea seems to have more phenotypic characteristics of alocasia than colocasia...very interesting. Sounds like a research paper is needed.Tony Avent
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"I consider every plant hardy until I have killed it myself...at least three times" - AventPeter Matthews wrote:
H. Yoshino, T. Ochiai and M. Tahara (2000) Phylogenetic relationship between Colocasia and Alocasia based on molecular techniques. In: D. Zhu, P. B. Ezyaguirre, M. Zhou, L. Sears and G. Liu (eds) Ethnobotany and genetic diversity of Asian taro: focus on China. International Plant Genetic Resources Institute and Chinese Society for Horticultural Science, Beijing. pp. 66-73.
A taro strain collected in Nepal in 1973 was considered to be an intergeneric hybrid between Alocasia and Colocasia, on the basis of chloroplast DNA analyses carried out in the 1980s (but see later work with isozymes, noted below).
Subsequently, an artificial cross was attempted and numerous seeds were obtained after a cross between C. esculenta var. aquatilis (Hassk.) Kitamura (from Nepal) and Alocasia brisbanensis (F. M. Bailey) Domin (ex Kyoto Botanical Garden). Most seeds did not germinate and only a single plant developed fully.
This plant was triploid and chromosome painting using genomic in situ hybridisation (GISH) showed that 14 of 42 chromosomes were derived from A. brisbanensis.
It was concluded that the plant was an intergeneric hybrid, formed as an unreduced egg of C. esculenta fertilised with normal A. brisbanensis pollen.
Isozyme analyses by V. X. Nguyen (1998), PhD, Okayama University, contradicted the original interpretation of the Nepalese hybrid, indicating that it was a cross between C. esculenta and C. gigantea (i.e. intra-generic, not inter-generic).
Comments by PJM:
Among other Asian accessions (Nepal and China) Nguyen found further examples of hybridsation between C. esculenta and C. gigantea. Taxonomically, C. gigantea is possibly misplaced in Colocasia, but it is not necessarily to be regarded as closer to Alocasia. As Yoshino points out, and as Tony Avent indicates in this list, there is much to be learned about hyribidisation among these aroids.
The experimental survival of a hybrid between genera was made possible by a rare polyploidisation event that allowed odd chromosomes to be carried along by a normal full complement of chromosomes.
Vigorous offspring are less likely after intergeneric crosses than after interspecies (intrageneric) crosses. An intergeneric crossing has not yet been proven to occur in the wild, though it is possible in principle.
Dear Pete and Marek:The Alocasia x Colocasia hybrid that you mentioned looks a lot like A. macrorhizos. I was fortunate to examine this hybrid several years ago growing at a Hawaii taro research station. It was found in an area of Nepal where the two genera grow together. On our expedition last year to N. Vietnam, we visited a restricted military area near the China border. We found Colocasia gigantea growing with Alocasia macrorhizos. Growing among them were several plants that superficially appeared to be bi-generic hybrids. We have not had these plants tested yet to confirm this yet, so this is just a preliminary observation. If anyone is doing work in that region, I will be glad to direct them to the population for further study.Tony AventPlant Delights Nursery @Juniper Level Botanic
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