Hybrid PalmsBy Geoff Stein (palmbob)
October 27, 2010
Though this may seem like sort of an unusual topic, the practice of hybridizing palms is not new. Many palms hybridize naturally, especially since so many related palms have been brought into proximity thanks to increased cultivation and collection of palms. Much of the time this ‘natural' hybridization in cultivation is not regarded in a positive light as it can be seen as diluting or impurifying the species. A common example of this uncontrolled hybridization is what one sees happening all the time with Phoenix palms in cultivation. There is so much hybridization within the genus that finding ‘the real thing' sometimes is very difficult. Reportedly most Phoenix reclinatas in cultivation are hybrids to one degree or another. This I assume explains the wide variation in appearance of this palm throughout California, Arizona and Nevada. Phoenix roebellenii also often have a bit of something else in them, as do many Phoenix canariensis, both common landscaping species. Where this becomes a real problem is is in the inland desert areas where the common Date Palm, Phoenix dactylifera, and all its carefully bred varieties and cultivars are at risk of being impurified by the local populations of landscape and backyard Phoenix palms.
These accidental hybrids are pretty hard to characterize in most situations and so other than guessing at the parents, little more can be said about them. In most situations when one encounters hybrid palms in cultivation, they are purposeful hybrids. These hybrids are either intrageneric, but most of the more interesting hybrids are often intergeneric (crossing of two palms of different, but related genera). The primary reason for hybridization honestly is curiosity and sales, as hybrid palms afford the avid collector something new, different and possibly unique. However there are other better reasons to hybridize palms that include improved vigor, improved cold hardiness and possibly improved quality, volume and hardiness of fruit or other economically useful palm part (eg. palm oil, palm hearts, fiber, 'wine' etc.).
Hybridization should not be confused with the creating of cultivars or varieties. Like all plants, there is some degree of natural genetic variation within the palms and not every single individual is an exact copy of every other. Variations made by nature are 'varieties'. This natural variation often results in some characterisics that a grower may want and want to select for. This forced 'evolution' or genetic engineering can result in the creation of many wanted 'cultivars' that are not a result of actual hybridization (the mixing of genetic material from different species).
This variegated Mediterranean Fan Palm (Chamaerops humilis- left) is a sought-after variety, but not a hybrid; Right is a photo of a date farm (Phoenix dactyliferas) in inland California where many varieties of carefully bred dates are grown. None are hybrids that I am aware of
These two varieties of Dypsis lutescens (Areca Palm) are very rare and sought after, but are cultivars, not hybrids, of the same species of palm.
When hybridizing palms, or any plant which has distinct male and female reproductive parts, the donor or pollen source is listed second, and the female or seed producer is listed first. One of the most popular and common hybrid palms in cultivation is the Butia x Syagrus (Butia capitata generally, and Syagrus romanzoffiana generally, though other species of each genus are more recently being crossed as well). These palms have Syagrus pollen and Butia seed.
Intrageneric hybridization is predictably, a bit more straightforward and has a much higher likelihood of producing viable seed. This is presumably because the genetic makeup, most importantly the chromosome number, are the most likely to be the same or close within a genus. Still there are many more obstacles to hybridizing than just putting two related palms together. In all purposeful hybridization undertakings, manual pollination is the only way to succeed, unless one has massive quantities of donor pollen available. Manual pollination rarely involves much more than ‘painting' the pollen onto the female plant parts either with a paintbrush, or dusting the female parts with pollen using a baster or syringe. Still, it's not that simple... The problems include:
•1. Collecting and preserving the pollen. Pollen is often available, but also sometimes really high up in a tree. Once collected, it must be filtered (to get out all the other ‘stuff- insects, plant parts etc.) sterilized (often heated in an oven) to keep it from succumbing to rot and bacteria, dried (same process and same reasons) and stored (put in a freezer normally in a paper container of some sort). How long it will remain viable that way is unpredictable, which can also complicate matters obviously
•2. Reaching the female flower when she's receptive is not always an easy thing to know. Receptivity supposedly can vary from days down to just hours in some species. I would personally be hard pressed to figure out when a flower was receptive. So this is obviously part of a learning curve one must deal with. Additionally, the flowers are often out of reach, particularly in really tall species (like Syagrus sp.).
•3. It is recommended the recipients own pollen (in species that are monoecious, meaning they have both male and female plant parts) be dealt with (sometimes putting a plastic bag around the inflorescence will rot the plant's own pollen) or else it might likely out-compete the donated pollen, or at least really complicate the situation since one will not be able to tell which seed contains a hybrid embryo and which does not, often for years after germination.
Most early work on intrageneric hybridization has been done with Syagrus, which is a bit unfortunate as many Syagrus are not markedly different in appearance, at least to less educated palm enthusiasts such as myself. But they are cheap and available. As mentioned above, very common intrageneric hybrids exist throughout the genus Phoenix, and occur with or without our help. There are dozens of examples of purposeful as well as accidental hybridization within this genus. Some of these hybrids are excellent landscape plants, but sometimes the hybrids can be annoying as well, particularly for landscapers who are looking for artful consistency, and end up with a variety of different looking palms.
X Syagrus 'costae' is probably the most well known of the intrageneric Syagrus hybrids- it is a hybrid of Syagrus coronata and Syagrus oleracea
Examples of intrageneric hybrids in the genus Phoenix : Here are two Phoenix hybrids (just assuming these are purposefulll they may not be): Phoenix paludosa x rupicola (left) and Phoenix canariensis x reclinata (right)
Phoenix reclinata x dactylifera (left) and Phoenix reclinata x roebellenii (right)
Phoenix rupicola x roebellenii (left) and Phoenix rupicola x canariensis (rigth)
Washingtonias (aka Mexican and California Fan Palms) are easy to hybridize, too, and they too also do it on their own. The cross between a Washingtonia filifera and Washingtonia robusta is often referred to as a Washingtonia x filibusta. There is some controversy, however, if these two species are really separate species. Not much is known about whether the offspring differ depending upon which species is the pollen donor.
Washingtonia robusta (left) next to Washingtonia filiferi (right in left photo)- one can see how close proximity may likely end in hybrid creation; Photo on right is of a young Washingtonia 'filibusta' (photo courtesy of tmccullo)
Hybridization occurs naturally in other genera as well, such as in Braheas. Brahea aculeata x armata can be found at the Huntington in California. These plants were collected from habitat in Mexico. A possible natural hybrid is Brahea clara, aka Brahea armata var. clara. This is now thought to be a natural hybrid between Brahea armata and Brahea brandegeei as it has too many differences from Brahea armata, some think, to just be a variety of it. Though in appearance it is somewhat similar, it does have the droopy leaves of brandegeei, but also is a much faster growing palm than armata. Additionally, and most compelling, is Brahea clara has a greater tolerance for humidity than does Brahea armata, so much so that it is grown relatively commonly in Florida, a climate where Brahea armata struggles mightily, with the only Brahea thriving there being Brahea brandegeei.
Brahea armatas in flower Brahea 'clara' (note the droopier, more folded leaves)
More interesting intrageneric hybrids involve the more exciting and diverse genera, such as Dypsis, a massive genus with incredible variation of appearance within the genus. Unfortunately many if not most Dypsis are rare, endangered or even extinct so there are ethical issues involved with hybridizing some of these species. But there are a few excellent hybrids with Dypsis leptocheilos, Dypsis decaryi, Dypsis cabadae and Dypsis madagascariensis, all relatively common species in cultivation.
Triangle Palms (Dypsis decaryis) are one of the more commonly used parents (left); Teddy Bear Palm (Dypsis leptocheilos) is one of the more common pollen donors (right)
Dypsis madagascariensis (single trunk form, aka Dypsis 'lucubensis'- left) is another popular hybrid parent; Dypsis cabadae (right) is a popular parent plant as well
Dypsis decaryi x leptocheilos (left) close up of triangular but fuzzy leaf bases (best of both worlds)- right
Dypsis leptocheilos x cabadae left (Thailand); Dypsis decaryi x cabadae right (California)
one of my favorites: Dypsis decaryi x madagascariensis
A palm grower in southern California recently created a wonderful intrageneric hybrid between two species of Rhapis (Lady Palms), naming the resultant offspring after his grandaughter. Rhapis ‘Alicia' is a wonderful potted and landscape plant that has some of the best characteristics of Rhapis humilis, a nice, tall and fairly hardy species, with Rhapis laosensis, a rare and tricky to grow species.
parents of Rhapis 'Alicia' hybrid: Rhapis humilis (left)- very tall and unweildy palm; Rhapis laosensis (right)- right size but fastidious plant
Rhapis 'Alicia' growing in garden of hybridizer, Louie Hooper (left); and in my garden (right)
Whether or not it can be argued that most or just a few of the intrageneric hybrids show much 'hybrid vigor' is not known (by me, at least). I cannot think of many of these hybrids that have much more vigor than either parent (Rhapis 'Alicia' being one exception), either in terms of cold hardiness, rate of growth, etc. Still, most are no worse for the experience, either.
Intergeneric hybrids: to successfully cross palms in different genera, they still have to be closely related. One cannot possibly hybridize a Mexican Fan Palm (Washingtonia robusta) with a Queen Palm (Syagrus romanzoffiana), though the offspring would probably look great, as these two palms are not even closely related. But even crossing Washingtonias with Trachycarpus sp. (Windmill Palms), both fan palms and somewhat related, would probably be impossible. As far as I know, all intergeneric palm hybrids are within the same taxonomic ‘subtribe'. Subtribes are the next step up in the taxonomy pyramid from genera, with Tribe and Subfamily being the greater divisions, all within the palm family (Arecaceae). Even trying to cross species across Tribes (like trying to cross Washingtonias with Trachycarpus- same tribe, but different subtribe) is very unlikely to work, and very often even within subtribes there is repeated failure. This failure occurs for a variety of reasons, I am sure, with the most important probably being the huge disparity in chromosome make up and numbers. For example, within the subtribe Butiinae, in which many successful intergeneric hybrids exist, a cross between a Jubaeopsis caffra (the Pondo Palm- a rare but cold tolerant species from South Africa) and Coconut palm (a very common but not cold tolerant species) would be extremely unlikely as one has about a hundred chromosomes and the other has less than 20. To this date that I know of, nothing has been successfully crossed with a coconut palm, yet not for lack of trying. A coconut hybrid could potentially be a huge economic goldmine, particularly if it could be crossed with something a lot more cold hardy. Sadly, it just happens to be too different despite its relatively closeness taxonomically to these other common palms.
The most common and well-known intergeneric hybrid is the Mule Palm, or X Butiagrus nabonnandii, a cross between a Butia capitata (Jelly Palm) and a Syagrus romanzoffiana (Queen palm, and the pollen donor). These palms are in the same subtribe, Butiinae. This hybrid is often sterile which is why it has the ugly common name of Mule Palm. It is, however, NOT ALWAYS sterile and numerous plants are growing in southern California from seed set off some of the older plants. So Mule Palm may turn out to be an unwarranted name after all. It is a beautiful, though extremely variable palm. As one might expect when hybridizing plants with different chromosome numbers, the offspring can be variable, far more variable than either parent species are. Some Mule Palms are bizarre and fascinating looking, while others are elegant and simply beautiful landscape palms. These hybrids display some of the best of hybridization with increased rate of growth (at least over one of the parents) and increased cold hardiness over both parent species. As it turns out, its ability to transplant well is maintained, too (both parent species tend to be among the most tolerant of palms to transplant as adults). It is a very popular cross for all these reasons, but my guess it is really popular because it is still quite rare and a real collector's find.
parents of the Mule Palm, Butiagrus: left- Butia capitata, Jelly Palm (the female component); right- Syagrus romanzoffiana (common Queen Palm), the pollen donor
Butiagrus photos- left is the old plant in the Huntington Gardens, southern California, which has ended up being a parent to hundreds of amazing offspring; right is an individual growing happily in northern California
more older Butiagrus- Ventura, California (left) and Orlando, Florida (right)
Two Butiagrus from the Huntington Butiagrus above- note how different these two individuals are, yet they were from the same seed stock
Butiagrus trunk, showing a lot of ornamental fiber, something neither parent plant usually has much of; Fresh Butiagrus seed (right)
The opposite hybrid, Syagrus X Butia, is also sometimes created, but is not nearly as easy to do as the female Queen palm (Syagrus romanzoffiana) is less apt to accept pollen from another genus as is a Butia female. Resulting seedlings often wither and die, too (not much ‘hybrid vigor' there). Why that is is not really well known. Of those rare individuals that survive, they seem generally to be taller and more like the Syagrus parent.
Another popular hybrid in this subtribe is Butia x Jubaea. Again, the resulting offspring show increased hybrid vigor with these palms showing some cultivational advantages over their parents. This hybrid is reportedly somewhat faster growing than either parent, a fairly good mix of the best of both parents in terms of size, color and overall looks, but has cold tolerance equal or greater than the parents, as well as much better tolerance to humidity than Jubaeas which are nearly impossible to grow in humid climates. Again, the main reason this hybrid is popular is because it is rare and a collector's prize.
Jubaea chilensis adult (left); right photo shows Jubaea (far left in background) and nicer Jubaea x Butia right
two photos of nice, older Jubaea x Butias in southern California
Other hybrids that have succeeded in this subtribe are those involving other species of Syagrus, Butia and both mixed with Parajubaeas, Jubaeas and sometimes a mix of three of the four genera. All these hybrids are extremely rare in cultivation, still, but all look like they have promise as excellent and vigorous landscape palms. The Butia x Jubaea that are then crossed with Syagrus pollen show another example of these intrageneric palms lack of sterility. This particular cross looks to have amazing potential as a landscape palm and the hopes are (as unlikely as it probably would be) that these multiple intergeneric hybrids will also be self reproductive (as they are fairly labor and time intensive products). Recently I discovered some Jubaea x Syagrus palms but these are extremely rare and reportedly very difficult to produce. Again, however, another beautiful palm hybrid creation!
rare and beautiful seedling of very rare Jubaea x Syagrus
Jubutiagrus seedling (left) showing characteristic twisted leaves of this hybrid; Jubutiagrus seedlings in the wings (right)
Recently a palm enthusiast in Southern California hybridized Lytocaryum weddelianum with the closely related Queen Palm, creating a remarkable, elegant and beautiful palm. And this individual palm has been readily self-producing viable seed, though the seed appears to have been pollinated back to the local Syagrus populations so the resulting offspring are looking more Syagrus-like.
parents of the 'Lytoagrus' below: Lytocaryium weddelianum (left) and Queen Palms (right)
rare and amazing hybrid, Lytocaryum x Syagrus (left) in hybridizer, Bill Dickenson's yard; right is one of its offspring, looking a lot more Queen Palm-like
One of the best hybrids to come along from a landscaping point of view in a completely different subtribe is the cross between Wodeytia bifurcatum and Veitchia arecina. This hybrid is commonly called the Foxy Lady Palm. These palms are both in the subtribe Ptychospermatinae. I do not know why someone decided to try this cross out of all the many hundreds of potential hybrids in all the various subtribes in the palm family. But it worked and the resulting offspring grow markedly faster than either parent and definitely have improved cold tolerance over both parents as well. And lastly, of course, they are unique and beautiful palms, and still on almost all palm growers want lists.
Parents of the Foxy Lady Palm below: Wodyetia bifurcata (Foxtail Palm) left; right is Veitchia arecina
Wodyetia x Veitchias (Foxy Lady Palms) in California
Variegated Foxy Lady Palm (left) in Hawaii; nice young plant in San Diego Zoo (right)
As one might guess, there are hundreds and hundreds of other potential hybrids to be created and experimented with. And with the increased availability of many of palms today that were nearly unheard of just twenty years ago, there is a seemingly limitless future of hybrid palm discovery. Still, the ethics of purposely hybridizing rare or endangered palms has to be kept in mind, and sadly, so many palms are finding themselves in these categories with all the habitat destruction around the world.
Parents of another fairly common hybrid: Coccothrinax species (left) and Zombia (Zombie Palm)- right
Coccothrinax x Zombia in Florida
For more on growing hybrids see the links below
For some lively discussion of palm hybrids, see these two links below
http://www.palmtalk.org/forum/index.php?showtopic=25523 - for a thread showing a photo of a Butia x Parajubaea