Tom,

I haven't tried the crosses, but here's an article about similar crosses with cotton.

Karl

Here is a link that might be useful: Wide Hybridization in the Malvaceae

1. Okra - chromosome number 130
2. Hibiscus syriacus - chromosome number 80
3. Marsh Mallow - Althaea officinalis - chromosome number 42, also 40
4. Hibiscus sabdariffa - chromosome number 72, also 18, 36
5. Hibiscus trionum - chromosome number 56, also 28
6. Malva neglecta - chromosome number 42.

The base chromosome number is 18. Although many of the hybrids will have fertility problems, because they are polyploids pairing of chromosomes in the F1 offspring might be reasonable in some combinations even when the counts differ between parents.

Here is a link that might be useful: Malvaceae Chromosome Counts

Recent work (Pfeil et al) has found Hibiscus to be divided into several clades, with several other genera embedded therein. Okra (Abelmoschus esculentus) and Hibiscus trionum belong to one clade, Hibiscus syriacus to another, and Hibiscus sabdariffa to a third.

Attempts to cross Hibiscus syriacus and Hibiscus rosa-sinensis, which belong to the same ("Euhibiscus") clade, have not been sucessful. Ditto attempts to cross Hibiscus rosa-sinensis with Lavatera thuringiaca, using cell-fusion techniques.

Here is a link that might be useful: Pfeil et al paper)