Cocoid Palm Hybrids
Cocoid palms are a related group of palm species belonging in the subtribe Butiinae of the palm family. They include some of the best known cold-hardy palms, including Butia and Jubaea, the queen palm Syagrus, the decidedly tropical coconut (Cocos), and a number of other less known tropical and subtropical species. While many of them are native to South America, a handful also originate in South Africa and Madagascar, and the native range of Cocos seems to be worldwide in the tropics.
One could say that palm growers in the Pacific Northwest constantly struggle to break the "Trachycarpus barrier" - it seems no other palm is quite so tolerant of our climate as good old Trachycarpus. So many larger, more exotic, and more tropical looking palms seem like they could almost grow here, yet the occasional cold winter keeps them just out of reach. This is irritating, but perhaps the curtain hasn't closed just yet on finding exciting and different palms for the Northwest. While just a few people have been hybridizing palms for many years; in general, hybrid palms are very much new on the scene. It remains to be seen whether hybrids of cocoid palms truly offer superior performance in the Northwest to naturally existing species - but if I didn't think the prospects were exciting, I wouldn't devote this much attention to them. I've written this article to lay out some of the possibilities for Northwest gardens.
COCOID PALM SPECIES AND THEIR LIMITATIONS
While much has been written in praise of hardy palm trees, here for brevity's sake I will describe the most important cold-hardy cocoid palms emphasizing the reasons why they are difficult subjects for the climate of the Northwest.
Butia capitata (Pindo Palm, Jelly Palm) from Brazil and Uruguay is easily the best known cocoid palm in US cultivation. It's quite hardy and often seems to do pretty well here for a long time - in fact, I wouldn't say it decidedly "doesn't grow here"; it certainly may in some sheltered gardens. Still, I am aware of no examples of mature, tree sized specimens in Northwest gardens, at least none that have survived in a Northwest garden continuously from their youth. The reason? This species tends to be aggravated by our long, wet winters and lose its center spear, especially if it gets too cold and moisture freezes in it. In our climate, once the center spear is lost, that usually means the palm is dead if left untreated, which it usually is. It also would prefer a climate with more summer heat - it grows very sluggishly here in our cool summers, and thus is slow to recover if it does get damaged. Really, it's impressive that this palm tolerates our climate at all, since it originates in a subtropical, almost frost free climate. But it is one tough cookie. It's quite variable as well. There are some nice silvery forms of it that would be a valuable attribute to impart to offspring when selecting potential parents for hybrids.
Other species of Butia are not to be overlooked. The most important of these is probably B. eriospatha, which is larger than B. capitata, originates at a higher altitude, and seems somewhat more amenable to cool summers and cold wet winters than its more common cousin. Also, B. yatay, a beautiful plant with silvery leaves, seems to be at least as hardy as B. capitata (although it's so attractive itself, one might not feel a need to improve upon it by creating a hybrid from it). There are also B. paraguayensis, B. odorata, and others, which are generally rather rare and similar enough to B. capitata not to have gained a huge amount of attention yet. While some Butia species are less cold hardy than B. capitata, others may prove to be quite hardy and valuable as hybrid parents.
Syagrus romanzoffiana (Queen Palm) from Brazil is probably the next best known cocoid palm. Planted by the gazillions in Mediterranean and subtropical climates, it's decidedly impossible to grow in the Pacific Northwest. It both needs more summer heat than we have, and can't handle our winter cold and wet. It just plain isn't hardy. A larger growing, high altitude form, dubbed "Santa Catarina" based on its place of origin, seems to be substantially hardier than those plants commonly in cultivation now. This very recent introduction deserves further trialing and is a vastly superior hybrid parent than a regular queen, if one wants the offspring to be cold hardy. While there are other species of Syagrus, they are nearly all hopeless as far as cold hardiness goes. Only one or two rare species from the highlands of Brazil, as yet too rare to be grown by all but the most enthusiastic collectors, endure significant frost in the wild.
Jubaea chilensis (Chilean Wine Palm) from Chile is a giant of a palm, and very beautiful too. All other factors being equal, I think it must be the cold-hardiest of the cocoid palm species. It is at its best in Mediterranean climates, and does not usually like climates with excessively hot or humid summers. I actually think this will grow in the Northwest, in the long run. Its problem is being preposterously SLOW GROWING, especially without a lot of summer heat. Not that it doesn't like our climate: we just don't tend to be patient enough with it. Those of us who are fortunate enough to have one feed and water it excessively to speed it along, only to find we have killed it with kindness when a cold winter comes along. It is a Mediterranean plant, accustomed to dry summers, and needs a chance to harden off even if it has only grown a little bit, in order to survive the winter. This magnificent palm also comes in a rare silver leafed form, which should be used for making hybrids whenever possible.
Finally, Parajubaea (Mountain Coconut) is a genus of three palm spceies from the high Andes, where they are subjected in the wild to copious rainfall and year-round cool temperatures. They are still rare, both in California and the Pacific Northwest. They are closely related to Jubaea, but are less hardy to cold, more tropical looking, not as enormous (but still rather large), and (fortunately) they grow a lot faster. P. cocoides, from northern Peru and possibly Ecuador, has been in cultivation in California since at least the 1980's. It's pretty much hopeless for the Pacific Northwest, since the fronds are only hardy to the mid-upper 20's F. P. torallyi and P. sunkha, both from central Bolivia, were introduced to US cultivation around the year 2000. Thus far, they seem to be hardy to the low 20's F or so, or perhaps even around 20°F if well hardened off. That's better than P. cocoides, but still not hardy enough for us. But at least all of them grow vigorously in cool weather, and in general are quite tolerant of cool and moist conditions. These are two important and very useful attributes when considering them as parents for hybrid palms that might thrive in the Pacific Northwest. And they are indisputably impressive, beautiful palms.
While other cocoid palms such as Allagoptera, Lytocaryum, and even Cocos have been considered or used in hybridization schemes, I won't discuss these here since they will not add anything of superior cold hardiness or adaptability to the parent species listed above. Still, as an aside, the pictures I've seen of rare Cocos x Butia hybrids are quite intriguing.
A hybrid is formed by taking pollen from the male flowers of a species and placing it on the female flower parts of another species when it is at the pollen-receptive stage of development. You then must wait for the seeds to mature, and the resulting plants, if they grow, will be hybrids. In this example, they would be first generation hybrids called F1 hybrids. A hybrid palm that sets seed, whether it be self-fertile or outcrossed (pollinated) with another palm, produces offspring that are called F2 hybrids. Subsequent generations would be F3, F4, etc.
The obvious question is, if cocoid palm species have trouble succeeding in the Pacific Northwest, why should hybrids of these very plants be expected to do any better? The answer is that hybrids, especially F1 hybrids (and many outcrossed F2, etc. hybrids), often show superior traits to their parents, often combining the most desirable features of each. In many cases, they may have improved vigor, climate adaptability, and beauty than either parent. For example, the cool and wet tolerance and quick growth of Parajubaea might be combined with the cold hardiness of Jubaea to produce a hybrid palm much better suited to our climate overall than either parent. Besides hardiness and adaptability, vigor is an important quality since it enables a palm to grow to a large enough size to reach its maximum frost hardiness in a short span of time, as well as recover quickly in the event that it is damaged in a cold winter.
The prospects sound exciting, but one caveat to keep in mind is that each plant is a genetically distinct individual. Thus there are always surprises, and hybrids of the same two parent species may not always produce exactly similar offspring. It's not out of the question that certain hybrids may demonstrate inferiority to both parents, although this seems to be much less likely to occur.
When writing palm hybrid names, the name of the mother plant is always indicated first. For example, a "Butia x Jubaea" palm is one in which Butia was the mother, producing the seeds, and Jubaea was the pollen donor. (The specific epithets of Butia capitata, Jubaea chilensis, and Syagrus romanzoffianum have usually been omitted in common practice, although I think greater specificity is beneficial to keep anyone from getting confused. For other palm species, one must be certain to include the specific names.) F2 hybrids can be indicated using parentheses, for example: "(Butia x Jubaea) x Butia" would be the offspring you get when a Butia x Jubaea mother plant is crossed with a regular Butia for a pollen donor.
It's important to keep track of which is the mother plant, since the traits of the mother tend to be somewhat dominant in the offspring. For example, a Jubaea x Butia will somewhat more resemble Jubaea, while a Butia x Jubaea will be more similar to a Butia. Certainly they are two different palms, although it is not always possible to tell which is which unless you are certain of the parents.
Much remains to be learned about the fertility of palm hybrids. Many of them seem to be self-fertile, or useful as pollen donors. Butia x Syagrus, with a very rare exception, is not fertile at all. Genetic variation certainly plays a role here as certain individual plants have proven to be less receptive to pollen, or not as good at producing viable seed, as others of the same parentage. (Frequently this is true of parent species as well-certain individuals just weren't meant to be good parents!)
A major limitation to hybrid palm cultivation in the Northwest will continue to be their availability. It's very rare that palms in the Northwest other than Trachycarpus set seed at all. One would have to wait many years after planting for most cocoid palms to flower, and then there is the problem of finding a pollen donor for a hybrid - and even then, there is no guarantee the fruit will be capable of ripening fully with our climate providing less heat than they might need. We will have to rely on sources from warmer climates for many years. Additionally, hybridization of palms can be a challenging technique to accomplish properly, often requiring specialization, much experience, and a generous helping of patience for a good seed set. Cocoid hybrids are likely to command top dollar for a long time to come.
COCOID PALM HYBRIDS AND THEIR POTENTIAL
Here are some of the cocoid hybrids that have already been achieved, with an emphasis on those that I think show the most promise for the Pacific Northwest.
Butia capitata x Syagrus romanzoffiana (Mule Palm) is the most widely known and widely planted hybrid palm. It is sometimes called "x Butyagrus". The common name "Mule Palm," referring to the fact that it is sterile like a mule, is not one I particularly care for, since it doesn't do justice to the beauty of this plant. Although quite variable it is always very attractive and tropical looking. Unfortunately I can't say it is really all that promising for Northwest gardens. If anything, it is less hardy than Butia, thanks to the genes of the Syagrus parent. However, crosses made using the "Santa Catarina" queen palms have shown much superior cold-hardiness and vigor in Europe. So that's worth looking into if they ever become available over here.
Butia capitata x Jubaea chilensis seems to be a winner. It's hardier than a Butia, faster growing than a Jubaea, very large, and most impressive. I think it has a good shot at growing here. Although less common than mule palm, this hybrid has been done numerous times in the past and is sporadically available through mail order and other sources. Butia x Jubaea is frequently, but not always, self-fertile, capable of producing its own F2 hybrid seedlings.
Butia capitata x Parajubaea cocoides has only been done by one person that I know of, but with impressive, even remarkable results. It has been documented to endure 14°F without any harm in a California garden (that for two nights during a prolonged freeze), which is especially surprising considering how P. cocoides isn't very hardy. It is also an exceptionally vigorous grower. Of course individual results may vary, but I would certainly invest in one of these if ever you have the chance to obtain one.
Jubaea chilensis x Butia capitata is, I think, a really excellent palm for Northwesterners to try. It ought to be nice and big like Jubaea but quite a bit faster growing. It is sometimes called "x Jubutia", but it should be noted that the reverse cross of these species cannot be correctly called x Jubutia.
(Jubaea chilensis x Butia capitata) x Syagrus romanzoffiana has been done by at least two people, I think. This palm can appropriately be called "x Jubutyagrus" without confusing anyone too much. Though I'm inclined to have reservations about anything that is half Syagrus (tender), this hybrid should make a hardier and larger growing alternative to Butia x Syagrus. If one were to hybridize (Jubaea x Butia) with a Santa Catarina queen, that would sure be cool.
(Jubaea chilensis x Butia capitata) x Jubaea chilensis has been done. This might end up being quite similar to a regular Jubaea with minor Butia-like traits.
Jubaea chilensis x Syagrus romanzoffiana has been done by at least two people, but, they say, it is a really difficult one to achieve successfully. Hybrid seedlings develop very large, stiff leaves and grow quite a bit more slowly than x Jubutyagrus. Still I think this would be an interesting one to try in the Northwest.
Syagrus romanzoffiana x (Jubaea chilensis x Butia capitata) has been done, and is essentially the reverse companion to x Jubutyagrus. Personally though I wouldn't want the frost tender traits of Syagrus to be dominant, so I'd rather have a x Jubutyagrus. That's just a guess though; perhaps this would be just as hardy - one never knows about these things until one tries!
Butia eriospatha x Jubaea chilensis was first achieved in 2009 by a gentleman in Brazil. This ought to be a definite winner for the Pacific Northwest, combining the vigor and cold-tolerance of B. eriospatha with Jubaea. However, finding one will be a problem for the foreseeable future. A reverse cross of these species would also be exciting to see.
Butia eriospatha x Syagrus romanzoffiana (Santa Catarina Form) might be worth a shot in the Northwest. One hopes it could be something that looks like a regular mule palm but is a whole lot hardier and better for the Northwest. I would definitely try it, but as yet, I think this hybrid has only been accomplished in Brazil and available in small numbers in Europe.
Butia yatay x Syagrus romanzoffiana has been done. I'd imagine this could be a very beautiful plant, but I would not be confident about its hardiness, given the dismal results with regular mule palm in our climate. A more exciting prospect might be a cross of B. yatay with a Santa Catarina queen.
I'm not aware of any hybrids having been accomplished with Parajubaea as the mother. Generally that's an impractical pursuit, since Parajubaea seed takes a very long time to ripen, and germinates erratically.
So that's what has been done to date - at least, according to all the information I can gather - in the realm of cocoid hybrids. I probably don't have to mention that it may be just the tip of the iceberg in the future of palm hybridization. It's easy to be inclined to make a list of all the palm hybrids we would like to see, and dream about them, but somehow this seems disrespectful or unappreciative of all the work and effort it takes to create them, for those who are able to do so. Either that or perhaps it's just an expression of enthusiasm. I'll use that last thought to justify my suggestion of how cool the following hybrids would be, if they were to be created.
Jubaea chilensis (silver form) x Parajubaea torallyi
All right, that's quite enough of my ideas... all this simply to illustrate that the possibilities are indeed endless. Hopefully by writing this article I've developed some interest, and readers will be inclined to bring some of them up to the Northwest and try them, when you have a chance to find them. Just remember not to be afraid to pay top dollar for them, be sure you know exactly what you're getting, and take good care of those babies!