Jeanne,

Congratulations. It's pretty.

Incompatibility between species is not always related to differences in chromosome number. It is possible to cross diploid and hexaploid roses, for instance. It may be that your hybrid is a tetraploid -- one set of chromosomes from D. knappii and 3 from 'Helen'.

It might be worthwhile pollinating your hybrid by 'Helen'.

Karl

Thank you for the suggestion, Karl. I think I'll try that.

Great one Jeanne. I've tried similar crosses myself and had little luck. Out of several pollinations, only two seeds ever grew. One died of misery and the other grew a small sickly plant that never flowered and eventually also died.

I've got some more knappii seedlings on the go now so am planning some more attempts this June.

The cross of white Dianthus plumarius x D. knappii has been made in New Zealand and was successful. D. plumarius is a hexaploid (6n). The researchers found that D. knappii produces unreduced gametes, that is some of its pollen or ovules instead of having n chromosomes have 2n chromosomes. The chromosomes of the seedlings were counted and some were tetraploids (3n + 1n = 4n) and some were pentaploids (3n + 2n = 5n).

The seedlings from the cross with the white plumarius were pale cream-yellow with some differences in intensity. Twenty crosses were made and four seedlings produced. Because the researchers found self-pollinations in early crosses they emasculated the flowers for subsequent crosses. D. knappii was the pollen parent in all crosses.

As a possible interest not all Dianthus allwoodii are hexaploid - a chromosome count of D. allwoodii 'Doris' found it to be 4n.