Leyland Cypress is capable of producing viable seeds, but rarely does so in practice as in the past generally only a single clone was grown at any one place so outcrossing was not possible. This has changed significantly in recent years, so viable seeds may well become commoner as the wider range of cultivars now planted reach seed & pollen production age.

There are over 20 Leyland Cypress cultivars; most of them result from separate Nootka Cypress × Monterey Cypress crosses, but a few are branch mutations of other Leyland cultivars.

With Nootka Cypress now classified in Cupressus together with Monterey Cypress (or both in Callitropsis, if you follow D.P.Little's ideas), there are now no intergeneric cypress hybrids, nor any intergeneric conifer hybrids at all.

What other Cupressus hybrids might exist has never been tested well, but unidentified, possibly hybrid, Cupressus trees are quite common in gardens in southern Europe. Unfortunately, no-one has the funding to do the DNA tests necessary to confirm these.

Cupressus × ovensii and C. × notabilis both produce cones; not sure if they've been checked for viable seeds, but I'd not be surprised if they did at least occasionally.

Resin

"Leyland Cypress is capable of producing viable seeds, but rarely does so in practice as in the past generally only a single clone was grown at any one place so outcrossing was not possible"

When you say "outcrossing" do you mean a particular leyland clone in proximity to a different leyland clone? I wonder if some other cypress pollen would be sufficient?

I ask about other hybrids because so called 'italian' cypress is so popular in mild climates - a hybrid with nootka cypress should produce a hardier, and probably faster plant. Who knows if the 'stricta' characteristic would come through though.

Probably not something I could try myself since I doubt I could keep an alsakan cypress alive in Texas.

Plants 77,

When you think of "false" cypress you're probably thinking of the Genus Chamaecyparis instead of ".

From your original post you say:
" Since there are a few cypress hybirds with a "false" cypress - is it fair to say that most cupressus species could hybridize with one another?" The answer is yes. Resin backs that up.

And yes, Resin is stating that the production of seed will be due to the presence of more cultivars within proximity of each other.

These are examples of what I think of as being "false-cypress."
Chamaecyparis pisifera or Chamaecyparis obtusa i.e. You have to now think in terms that Chamaecyparis nootkatensis, no longer exists...except on old paper only. One more thing to make sure you're on track is that Nootka Cypress (probably a simple overlook on your part) is not "alaskan yellow cedar", just to clarify. It's never been a "cedar", only a true, "'false cypress'."

Resin, that guy 'Little'? What the hell is he thinking??
You just defied logic with a few sentences. Can you clarify if I'm missing something here or is that guy right in some way. That makes no sense when it's already know that cultivars were derived from within two cypress species crosses? Like I say, am I missing something here, or is this guy gone fishin'?

Thanks,

Dax

There's no definite evidence of any Old World cypress (OWC) New World cypress (NWC) hybrids - some possibles have been noted, but haven't been tested yet.

D.P.Little reports some genetic differences between OWC and NWC, with the suggestion that the latter may be more closely related to junipers than they are to OWC; the evidence is not wholly conclusive yet, but was enough to make DPL transfer all the NW cypresses to a separate genus Callitropsis. But a Chinese study also put Nootka close to several Chinese species, so DPL's ideas are as yet far from firm. There's also (even more recently) been some further splitting suggested by Bartel & Adams, including a new genus Hesperocyparis, I'll post more and dig out the references later. It's all getting into a horrible nomenclatural mess!!

Resin

It's interesting that nobody is referring to the Nootka tree as Xanthocyparis. Has that fad already expended itself?
What is needed is for a rich cypress-lover to die and endow an institute devoted to cypress genetics, like the Institute of Forest Genetics at Placerville, CA originally funded by James G. Eddy for Pinus. If Old World Cypresses and New World Cypresses were generally crossable within each group but not across groups, then Little's placement of the latter into the new genus Callitropsis would have pretty persuasive support, even without DNA analyses. But even without biological backing like that, Little's new names for the individual NWCs are legitimate if he dotted all the i's and crossed all the t's. Of course you are not obligated to use them. As for when evidence is "wholly conclusive", that is a judgement call made individually by anybody who wants to play. Where is that rich cypress-lover when you most need him/her?

Maybe Xanthocyparis nootkatensis is a Chamaecyparis
as it was called Chamaecyparis nookatensis so maybe
Xanthocyparis vietnamensis is also a Chamecyparis.
Anyone know what species of Cupressus will be classified
under Hesperocyparis?

Hi Blue Yew
Maybe it's these new hybrids generating seed. It kinda makes sense right now. Callitropis vietnamenis is what sprung up a lot of this or was one of the first things to cross my mind in regards to where this conversation might have headed. Now I see on Google that's how DPL listed this discovery whereas Farjon clips it as Cupressus vietnamensis. I'll be interested to hear more. It's already evident though that how we all classify things in current fluct are ...interpretative.

Hi Pinetree, I've given up on Xanthocyparis... it's probably going to be like this 'new' Hesperocyparis. Never even heard of "Hesperocyparis." This is getting ugly.

This is a list I saved Resin wrote (2007):

Chamaecyparis. Asia, North America; cones mature in 6-8 months.
Chamaecyparis formosensis - Formosan Cypress
Chamaecyparis lawsoniana - Lawson's Cypress
Chamaecyparis obtusa - Hinoki Cypress
Chamaecyparis pisifera - Sawara Cypress
Chamaecyparis taiwanensis - Taiwan Cypress
Chamaecyparis thyoides - White Cypress
Callitropsis - may be better regarded as a synonym of Cupressus, at least for the time being pending further DNA tests. North America, one in Vietnam; cones mature in 18-25 months (selected examples only):
Cupressus arizonica (syn. Callitropsis arizonica) - Arizona

Cypress
Cupressus bakeri (syn. Callitropsis bakeri) - Modoc Cypress
Cupressus glabra (syn. Callitropsis glabra) - Smooth Arizona Cypress
Cupressus lusitanica (syn. Callitropsis lusitanica) - Mexican Cypress
Cupressus macnabiana (syn. Callitropsis macnabiana) - MacNab Cypress
Cupressus macrocarpa (syn. Callitropsis macrocarpa) - Monterey Cypress
Cupressus nootkatensis (syn. Callitropsis nootkatensis) - Nootka Cypress
Cupressus sargentii (syn. Callitropsis sargentii) - Sargent's Cypress
Cupressus vietnamensis (syn. Callitropsis vietnamensis) -
Vietnamese Cypress

Cupressus, in the restricted sense. Eurasia, North Africa; cones mature in 18-20 months (selected examples only):
Cupressus atlantica - Moroccan Cypress
Cupressus cashmeriana - Bhutan Cypress
Cupressus dupreziana - Saharan Cypress
Cupressus funebris - Chinese Cypress
Cupressus sempervirens - Mediterranean Cypress
Cupressus torulosa - West Himalayan Cypress

Sources:
Gadek, P. A., Alpers, D. L., Heslewood, M. M., & Quinn, C. J. (2000). Relationships within Cupressaceae sensu lato. A combined morphological and molecular approach. American Journal of Botany 87: 1044-1057.

Little, D. P., Schwarzbach, A., Adams, R. P., & Hsieh, C.-F. (2004). The Circumscription and Phylogenetic Relationship of Callitopsis and the Newly Described Genus Xanthocyparis (Cupressaceae) American Journal of Botany 91: 1872-1881.

Xiang, Q. & Li, J. (2005). Derivation of Xanthocyparis and Juniperus from within Cupressus: Evidence from Sequences of nrDNA Internal Transcribed Spacer Region. Harvard Papers in Botany 9: 375-382.
Little, D. P. (2006). Evolution and Circumscription of the True Cypresses (Cupressaceae : Cupressus). Systematic Botany 31: 461-480.

Seems I'm using DPL "Callitropsis" placement for vietnamensis. It was just an internet article I read quite a while back. A little photo on a mountainside accompanied it.

Dax

And to add to the list above, the known crosses are :

Leyland Cypress - Nootka X Monterry

Notabilis (Alice Holt) Cypress - Nootka X Arizona Cypress (smooth-bark)

Ovensi Cypress - Nootka X Luscitanica

Are there any other known crosses of Cupressus?

Just to note:

one problem with common names, Moroccan Cypress has been used to refer to Tetraclinis articulata

second, this may not be in the tone of this discussion since this is more a toxonomic discussion, but natural macnabiana X sargentii hybrids are common where these overlap in the inner Coast Ranges of California. I believe Resin among others has experience with this population?

"What is needed is for a rich cypress-lover to die and endow an institute"

All donations will be gratefully received ;-)

"If Old World Cypresses and New World Cypresses were generally crossable within each group but not across groups, then Little's placement of the latter into the new genus Callitropsis would have pretty persuasive support, even without DNA analyses"

That is equally, through the known hybrids, a very persuasive argument for not splitting Callitropsis / Xanthocyparis separate from New World Cupressus as done by Farjon, or the multiple genera accepted by Adams et al. (see below).

"This is a list I saved Resin wrote (2007):" Hi Dax - thanks for saving me a lot of typing!! There's something gone wrong with the formatting a little above, it should read:
....
Chamaecyparis thyoides - White Cypress

Callitropsis - may be better regarded as a synonym of Cupressus, at least for the time being pending further DNA tests. North America, one in Vietnam; cones mature in 18-25 months (selected examples only):
Cupressus arizonica (syn. Callitropsis arizonica) - Arizona Cypress
Cupressus bakeri (syn. Callitropsis bakeri) - Modoc Cypress
....

Since writing that, I've got more in favour of retaining a broader view of Cupressus, not separating Callitropsis. One important paper is Mu et al. (2006), Application of pet G-trn P sequence to systematic study of Chinese Cupressus species, Frontiers of Biology in China 4: 349-352; their results place Nootka in a tight group with Cupressus funebris and Cupressus duclouxiana, these three close to Cupressus torulosa and rather less close to a Cupressus chengiana Cupressus gigantea pair, which makes separating Callitropsis very problematic.

Adams, Bartel & Price (Phytologia 91: 160-185, April 2009) have recently treated the NWC (excluding Nootka) in a new genus Hesperocyparis, with Nootka in Callitropsis and Vietnamese Cypresses in Xanthocyparis (i.e., four genera of "true" cypresses!!), but their analysis doesn't include any of the Chinese Cupressus, so doesn't give a full picture of potential relationships.

"one problem with common names, Moroccan Cypress has been used to refer to Tetraclinis articulata"

New one on me; best ignored as unhelpful, I guess! Tetraclinis usually goes by the common name Sandarac.

"second, this may not be in the tone of this discussion since this is more a toxonomic discussion, but natural macnabiana X sargentii hybrids are common where these overlap in the inner Coast Ranges of California. I believe Resin among others has experience with this population?"

Yep, that's right; I saw some presumed hybrids at the north end of Indian Valley Reservoir (39°10'N 122°32'W); both parent species also present there. I read recently somewhere that this hybrid (long presumed) has now been genetically verified.

Resin

The taxonomy stuff is lost on me, but with respect to the hybrids and their fertility, it seems like all the hybird cypress in cultivation are f-1 crosses, with the exception of some leyland cultivars that arose as sports on an f-1 cross.

So if they did produce viable seed, is it fair to say the offspring would differ markedly from the hybird parent? I thought the way it worked was the F-1 generation was pretty uniform and intermediate between parents, but that next generation is not as uniform and could be a throwback to either parent, so you could have a plant very similar to standard alaskan cypress, mexican cypress, whatever. If that's the case then most (maybe all)of the seedlings would not be as useful as the clone they came from.

I say that because the hybrids are desireable because they represent a compromise between very different parents. They take some cold hardiness and disease resitance from one parent (alaskan cypress) and fast growth and heat tolerance from the other (arizona cypress or mexican cypress), making a middle of the road plant that's useful to more people.

I also wonder why everyone is so turned on by leylands which are ubiquitous, but the other crosses, which seem to me as good or better, are almost impossible to find in cultivation.

Lowes and home depot sell tons of leylands where I live in texas and either of the other hybids would almost definitely be better.

"it seems like all the hybird cypress in cultivation are f-1 crosses"

Seedlings have been reported from Leyland Cypress seeds, so F2 plants do exist (not seen any myself, though). Sports (vegetative mutations) from F1 plants still count as F1, though.

"So if they did produce viable seed, is it fair to say the offspring would differ markedly from the hybird parent?"

I guess they'd show a range of variation between the two original parents; given that cypresses are difficult to identify at the best of times, picking up F2 hybrids won't be at all easy unless they were produced by controlled pollination with known parentage

"making a middle of the road plant that's useful to more people"

Hmmm . . . middle of the road isn't a good place to be, high risk of getting run over, and the danger can come from two directions at the same time ;-)

The susceptibility of Leyland Cypress to Seiridium canker is perhaps a good illustration of this!

"but the other crosses, which seem to me as good or better, are almost impossible to find in cultivation"

You'd need to ask the commercial propagandists about that! Of course Leyland has had the best part of 60 years advantage over the other two. C. × ovensii isn't anything very special, but C. × notabilis is rather attractive I think.

Resin

I've got a bunch of young Notabilis and Arizona Cypress in pots. So far nothing very dramatic to report about them one way or the other. The Arizona Cypress seem to have better root systems so far and perhaps more drought resistance. The Notabilis have thicker stronger trunks, thicker foliage, and seem to have grown slightly more.