Was under the impression that "Glabra" was native to a small part of California.
How far apart were the two parent trees? How big is the hybrid? Approximate location? Any noticeable traits evident yet?
I planted several "wild" Smooth-Bark Cypress at the house. Have currently switched to planting Rough-Bark Cypress. Wondered if they would mix and if I would eventually have to cut down my older Smooth-Barks to maintain seed purity of the Rough-Bark Cypress. Wonder at what distance the two varieties become too close.

There are no Cupressus glabra or arizonica native to California. Botanists looking at herbarium specimens have previously placed Cupressus nevadensis and stephensonii in "arizonica", but this has been proved wrong by molecular testing, as well. I have seen the hybrid, it is about thirty feet tall and located near Central Point, Oregon. It looks like...well, a hybrid between goveniana and glabra.

Any Cupressus native to North America are liable to hybridize with each other. Cupressus macrocarpa and nootkatensis (the parent trees of Cupressus x leylandii) were supposedly about 300 meters apart from each other when their pollen mixed in a British Garden 90 years ago...the wind can carry microscopic pollen grains quite far.

Shastensis,
I guess you are late with your wish. The great urban areas of California are since long ago full with different and powdering cypresses from many nurseries.

What you could help? I think, if there are natural old, undisturbed reserve stands of the specieses you like in California, is helping them to keep them in one without powdering 'pollution'.

On the other hand, the urban areas are very good places to select hybridized cypresses, which could have a value in the future in gardening. I hope, that the arizonicas are not "enemies" for you.

Zsolt

The only Cupressus that are a threat to California Cypresses are glabra and arizonica...the European, Asian and and Northern African Cupressus are too distantly related to be of any potential to hybridize. They will soon be in a separate genus, anyway. Arizonica and glabra are fine trees, I have seen them in the wild. I just think it is a shame that they are used so commonly in this state (California) when 1. They pose a threat to genetic purity of wild populations and 2. There are so many options of Native California Cypress that are just as fascinating and beautiful, often more so. The California Cypress need to be planted MORE, the arizonica and glabra LESS, at least in the state of California.

"Cupressus macrocarpa and nootkatensis (the parent trees of Cupressus x leylandii) were supposedly about 300 meters apart from each other when their pollen mixed in a British Garden 90 years ago...the wind can carry microscopic pollen grains quite far"

That's just one of the crossings (the first known one); in the Stapehill case (verified same parentage by chemical analysis), no Nootka Cypress was found anywhere in the area that the Monterey Cypress seeds were harvested. So the pollen can blow several kilometres.

Yes, agree it has the potential to be a serious problem for the future.

Resin