And how about the leaves? As a kid I got tired of raking Catalpa leaves. The smaller Chitalpa leaves are less messy when they fall. I suppose the second generation plants lean more towards the Catalpa.

I hope further developments do not improve too much in fertility. Catalpa seed pods are unsightly and messy -- though I was told years ago that they make good food for cultivated earthworms.

Karl

But in most cases a plant's ability to produce viable pollen is correlated with its ability to produce viable ovules, so it'll be just as useful for pollinating other plants as it is for producing seed. Only thing in your favor on that is that far more pollen than ovules are produced, so given the same incidence of fertility in each you're more likely to get some fertile pollen than some fertile ovules...

Patrick Alexander

Cytoplasmic components (organelles) may segregate if the hybrids receive some from both parents. In some Oenothera and Epilobium hybrids the seedlings have either green leaves or albino (white or yellow) depending on the direction of the cross. Sometimes the green-leaf types will produce spots or flakes of yellow (or white), indicating segregation of chloroplasts.

Similarly, and in similar numbers, other organelles (mitochondria?) may segregate allowing an occasional anther to become fertile and bear functional pollen.

Not all sterility results from incompatibility of chromosomes.

Karl King