Hybridized palm trees are not a new phenomenon. Palms do hybridize naturally. For decades the natural crossing of palms have produced more cold tolerant, humidity tolerant, and soil tolerant plants. A good example of this is the Phoenix palm varieties. In Arizona, California, Nevada, and Northern Mexico where these are so densely propagated and farmed they often mix with other palms. The Phoenix roebellinii and Phoenix canariensis are both often grown with a strain of some other palm in them. This explains why the Phoenix Canary Island date palm can look completely different in Palm Springs than it does in Las Vegas and even the Gulf Coast.
HYBRIDIZATION OF POPULAR COCOID PALMS LISTED
Butia capatia: (Pindo Palm) from Brazil and Uruguay is easily the best known cocoid palm in US cultivation. It's quite hardy and does well in USDA Zone 8a; 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. 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 Zone 8a as sooner or later the low temperatures will kill it. It both needs more summer heat, and can't handle the winter cold and wet. It just isn't hardy below 25F. 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 all less cold hardy. Only two rare species from the highlands of Brazil at the 3000 ft elevation, the Syagrus romanzoffiana var. litoralis "Silver Queen" and the Syagrus romanzoffiana "Santa Catarina", only found grown by 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, it is 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 however we have this palm growing here on the Mississippi Gulf Coast and doing well. This palm is the most excessively SLOWEST GROWING. Anyone fortunate enough to have one of these Jurassic like palms work excessively to doing everything to help speed up its growth. 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.
Parajubaea: (Mountain Coconut) is a genus of three palm species from the high Andes, where they are subjected in the wild to excessive rainfall and year-round cool temperatures. 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 in Zone 8a 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 USA cultivation around 2000. They seem to be hardy to the low 20's F or perhaps even around 20°F if well hardened off. That's better than P. cocoides, but still not hardy enough for Zone 8a. 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 Zone 8a including the Carolina's and the Pacific Northwest. And they are very impressive and beautiful palms.
Phoenix Canary Island:
AVAILABLE COCOID PALM HYBRIDS
Here are some of the cocoid hybrids that have been achieved, with an emphasis on those that show the most promise for USDA zone 8a.
Butia odorata x Syagrus romanzoffiana “xButiagrus nabonnandii F1”: (Mule Palm). This hybrid palm is the most widely known and widely planted hybrid palm. It is called "X Butiagrus". The common name "Mule Palm," referring to the fact that it is sterile like a mule. Although quite variable it is always very attractive and tropical looking. It is less hardy than Butia, due to the genes of the Syagrus romanzoffiana parent. However, crosses made with Silver Queen Palms (Syagrus romanzoffiana var. litoralis) are more cold hardy and by using the Syagrus romanzoffiana "Santa Catarina" mountain queen palm the even more hardy mule palm has shown much superior cold-hardiness and vigor in Europe.
Butia odorata x Jubaea Chilensis “x Butijubaea F1”: This hybrid is a winner for zone 8a. It is more cold hardy than a Butia, and faster growing than the Jubaea, very large, and most impressive. Although less common than mule palm. Butia x Jubaea is frequently, but not always, self-fertile, capable of producing its own F2 hybrid seeds.
Butia odorata x Parajubaea cocoides: With impressive, even remarkable results. It has been documented to endure 14°F without any harm in a North 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.
Jubaea chilensis x Butia odorata "x Jubutia F1": Is a really excellent palm for zone 8a. It has a very robust trunk 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 "xJubutia"
Jubaea chilensis x Butia odorata x Syagrus romanzoffiana “x Jubutiagrus F1” 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 definitely be more cold hardy.
Jubaea chilensis x Syagrus romanzoffiana “x Jubagrus F1”: A really difficult hybrid to achieve successfully. Hybrid seedlings develop very large, stiff leaves and grow quite a bit more slowly.
Butia eriospatha x Jubaea Chilensis: This hybrid palm was first achieved in 2009 by a gentleman in Brazil. This ought to be a definite winner for zone 8a, 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 var. Santa Catarina: Should look like a regular mule palm but is a whole lot hardier and better suited for zone 8a. We are looking forward to making this hybrid available for our customers by 2020. This hybrid has only been accomplished in Brazil and now available in small numbers in Europe.
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 out-crossed (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 USDA Zone 8a 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, F3, F4... 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 Zone 8a 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 are exciting however the conditions or limitations 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 identical 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. Generally by the time a hybrid crop is 3 years old the weak less tolerant specimens have died during the winters or removed because of slow growing traits.
Hybrids nomenclature always indicated mother 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 botonical names Butia capitata, Jubaea chilensis, and Syagrus romanzoffianum or Syagrus romanzoffiana var. litoralis, etc. should always be use to minimize confusion. F2 hybrids are seen 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 dominant in the offspring. For example, a Jubaea x Butia will more resemble Jubaea, while a Butia x Jubaea will more resemble 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, is a rare exception, it 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.
A major limitation to hybrid palm cultivation will continue to be their availability. 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 producing a viable seed that will successfully germinate. 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.