Unlike some other families (e.g. Cactaceae, Orchidaceae) of flowering plants intergeneric hybrids are relatively scarce in Malvaceae. One might expect more reports of intergeneric hybrids in economically important genera, such as Gossypium (cotton), Theobroma (cacao) and Abelmoschus (okra), but even here, unlike Triticum/Hordeum/Secale (wheat, barley and rye), Saccharum and Brassica/Raphanus (cabbages etc. and radish), reports of intergeneric hybrids are scant.
A paper on Amazonian Theobromas  cites an earlier report of an experimental hybrid [a] between Theobroma cacao and Herrania mariae.
A 1980 paper reports a hybrid between Gossypium hirsutum and Hibiscus panduriformis . This paper also cites a paper from the Soviet Union [b] reporting hybrids between Gossypium on the one hand, and several other genera of Malvaceae; including Abelmoschus, Althaea (from other mentions of this paper I expect that this is Alcea rosea), Malva and Abelmoschus, and two papers from China [c, d] reporting the production of hybrids between Gossypium hirsutum and/or arboreum with Hibiscus rosa-sinensis.
Gossypium was earlier divided into several genera. Known experimental hybrids in this genus include hybrids between several of the previously recognised genera.
Hybrids (×Alcalthaea) are known between Alcea and Althaea .
Hybrids are known between Malva and Lavatera in their traditional circumscriptions. Most of these become intrageneric hybrids under more modern conceptions of the genera. However a hybrid between Lavatera trimestris and Malva 'Bicolor' is reported , and Malva alcea has been identified as a palaeohybrid of Malva moschata and Lavatera thuringiaca.
The name ×Malvalthaea transcaucasica is applied to putative (palaeo?)hybrids between Malva aegyptia and Althaea hirsuta, but this is another instance where both parents are now placed in Malva.
A hybrid between Chiranthodendron and Fremontodendron was raised in California [e], and is grown in a small way as an ornamental tree. This has been named ×Leelenzia ranchorum and ×Chiranthofremontia lenzii (if I interpret the ICBN correctly neither name is valid under the provisions of the code), and more recently as Chiranthomontodendron lenzii.
A hybrid Anoda thurberi × Periptera punicea is reported. 
Gossypium hirsutum × Hibiscus panduriformis
It is reported that a single viable seed of this hybrid was obtained from 2,000 pollinations of a male-sterile Gossypium hirsutum, representing a hybrid production rate of less than 0.01%, even in the absence of competition from cotton pollen.
The hybrid is generally intermediate between its parents. It is an annual, which shares with cotton the presence of gossypol glands, foliar and involucral nectaries, and a fruit in the form of a boll, and with the other parent the presence of hairs on all vegetative parts. The leaves are cordate (like both parents), and 3-5 lobed, but not as deeply as in cotton. The bracteoles number 3. They are laciniate, as in cotton, but not cordate. The calyx is campanulate. The corolla favours Hibiscus panduriformis in its yellow colour with a darker central spot. The anthers are arranged as in Hibiscus panduriformis.
Meiosis in the pollen of the hybrid was investigated. It has 38 chromosomes (intermediate between the 52 and 24 chromosomes of the parents). During metaphase there are up to 19 bivalents, but most commonly 12 or 13 (which is still higher than is common in haploid Gossypium hirsutum - possibly Hibiscus panduriformis is also a palaeotetraploid). Segregation of chromosomes during anaphase was assymetric, with the common division being into groups of 12 and 26 chromosomes, which suggests to me reconstitution of the parental genomes. Pollen fertility is about 60%. The hybrid is fertile, but seed set is lower than in the parents.
Surprisingly none of the reports of intergeneric hybrids with Gossypium seem to have been followed up. However, the report of a hybrid with Hibiscus panduriformis seems to be robust, which suggests that wide hybrids can be obtained in Malvaceae, if sufficient attempts are made. On the other hand attempts to create hybrids by somatic cell fusion of Hibiscus rosa-sinensis and Lavatera thuringiaca have been unsuccessful, and the application of Abelmoschus esculentus pollen to Gossypium results in the development of chromosomally abnormal cotton plants [f]. (Compare with the production of haploid wheat plants by fertilisation with maize pollen.)
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© 2008, 2011 Stewart Robert Hinsley