Caution - Dangerous Crossing

Don't be alarmed, but there is a problem in the palm world, which you ought to know about...
Martin Gibbons, The Palm Centre, 563 Upper Richmond Road West, London, SW14 7ED, U.K.
Chamaerops No. 13, published online 23-08-2002

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X Butiagrus nabonnandii, in S. of France.

If you grow palms, you will be interested, maybe even a little alarmed, by a problem that has recently come to light, and which is being talked about more and more by those in 'the palm business', whether amateur or professional. It is a problem of concern particularly to those of us who grow palms from seed; however, because of its insidious nature, it can actually affect all of us. You will perhaps never look at your palms in quite the same way again. And you will certainly be more careful about buying them, either as plants or as seeds, in future.

It is the joint problem of cross-pollination and consequent hybridisation.

There is an understandable tendency for botanic and other gardens, both public and private, to plant palms of the same genus in the same area. It is a natural enough plan since identification of individual species is most easily accomplished if they are grouped with their close relatives; comparisons can be made without difficulty. However, since many palms hybridise freely with closely related species it is extremely likely that female flowers will be fertilized with pollen from male trees of other species growing in the same area. Development of the fruits continues in the normal way, and the resultant seeds may well appear identical to those of the pure species. O.K. you may say, so what's the problem?

The problem is that many seed collectors and dealers make their collections in these same gardens. They are easily accessible, the trees are readily identifiable, and seed collection is easy. The seed collected from a Phoenix sylvestris will be sold as such, but it may be 50% Phoenix dactylifera. The seed collected from a Sabal minor also will be sold as such, but it may be 50% Sabal palmetto. The Trachycarpus martianus in Huntington botanical gardens in California, from which most young plants in cultivation around the world have come, are rumoured to be all female. Are they pollinated by male Trachycarpus fortunei?

The characteristics that enable the expert to tell hybrid from pure species may not become apparent for many years, perhaps not even until the young plant itself has begun to produce its own flowers and fruit. Perhaps not even then. But certainly the genes of both parents will be passed into its seed and will corrupt any future plants produced from it.

The sharp-eyed palm enthusiast can spot probable hybrids easily in many a botanic or public garden. In the south of France, for example, you can find many examples, suggesting that this problem has long been occurring. Phoenix reclinata with very thick trunks; Phoenix canariensis with red fruits; Phoenix dactylifera with green leaves; Sabals with characteristics of both S. minor and S. palmetto, or half a dozen other species.

Some hybridisation results in wonderful plants. The famous hybrid between Syagrus (Arecastrum) romanzoffiana and Butia capitata (which used to be called 'X Butiarecastrum nabonnandii', after the French botanist who first made the cross, and is now X Butyagrus nabonnandii) is a most beautiful tree with the clear characteristics of both parents. The seeds that it produces however are sterile. Some crossing of different species of Chamaedorea has produced some excellent plants too. But a collection of them, unchecked, is likely to produce seeds of unknown parentage with quite undesirable qualities. If and when these pass into other collections, the resultant permutations and confusion can only be imagined.

Over the millennia, palms have evolved into thousands of distinct species. With mans' obsession with collecting, this trend is actually being reversed. Hybridised seeds are distributed around the world at great speed. No checks are made on the authenticity of their parentage, and like a computer virus the problem can spread from one town to another, one collection to another, one country to another.

For instance, an innocent palm enthusiast in, say, South Africa or Australia, purchases seeds, by mail order, from a distributor on the other side of the world. This distributor, in equal innocence, may have in turn bought the seeds from a collector who gathered them from underneath a correctly labelled tree in a public, private or botanic garden. The enthusiast will germinate the seeds and plant the resulting young plants, entirely unaware that they may actually be hybrids. So far, no problem. But when his trees mature and begin to produce their own seeds, which he sells, the predicament begins to spread, which is why the comparison with a virus is such an apt one. Within a few generations (not long with some fast growing species) the problem is insoluble, and if the seeds are widely circulated, a nightmare.

An excellent example is provided by Trachycarpus takil first introduced into Europe from Himalayan India by a Major Madden in I 853 when he distributed young plants to several gardens and well-known nurserymen of the day. History does not record what happened subsequently, but it is likely that because of the only subtle differences between T. takil and T. fortunei; which was beginning to become popular around that time; no steps would have been taken to prevent them from interbreeding. The resultant seedlings would likely have been distributed by those unaware of the dangers, and they, when grown, would in turn have interbred again with T. fortunei It is not too fanciful to suggest that every T. fortunei that you see, has actually some T. takil 'blood' flowing in its veins. Perhaps it is this that causes some of the great variability in the species. Some with deeply divided leaves, some not. Some which shed their fibres naturally or don't. Some with glaucous leaves or not. And so on and so forth.

Only fresh importations of seed from China can carry the guarantee of purity but unless care is taken, these plants will in turn interbreed with the 'corrupted' T. fortunei/T takil and the problem begins all over again.

So what is to be done? It's tricky. Nobody wants to destroy their collection and begin again. Certainly those in charge of botanic gardens and other important collections of palms (especially those from which seeds are collected commercially (or even illegally)) should take steps to prevent cross-pollination between species. It is difficult but not impossible. If pure seed from a particular species is required, the inflorescences of all related species flowering at the same time should be removed. This is especially important with rare species or in cases where the palm is perhaps extinct in the wild. Extreme caution should be applied in maintaining the purity of these species; there may not be a second chance. Care should also be taken with new plantings to ensure the purity of the plants and in avoiding the temptation to group different species together.

Seed sellers should state that parentage is uncertain if the seeds are collected in a botanic garden where there is even a chance of crosspollination. And of course, wild collected seed has an extremely good chance of being pure. Nature has arranged this, either by having related species occurring at a safe distance from one another, or by having them flower at different times. This is not intended, however, as an invitation to collect seeds from the wild; this poses an altogether different set of problems.

Not all palms can suffer from the dangers outlined. Monotypic genera (those with only one species) are an obvious example. You are unlikely to run into problems with Rhapidophyllum, Serenoa or Chamaerops, to name a few. Additionally, isolated, monoecious (both sexes on the same plant) palms in botanic gardens can be considered relatively 'safe'; they are much more likely to be self-pollinated than fertilized with pollen from a distant neighbour.

It is up to all of us involved in 'the palm business' whether commercially or privately, to be aware of the dangers and to take a responsible stance. Only in this way can this worrying and potentially devastating problem be reversed.

Readers Comments:

On 3-9-2002 Dan Schilling wrote:
Seed for Thought
An excellent point, Martin! Methinks I will be looking more closely at my young Trachycarpus sprouts (Takil, Wagnerianus, Fortunei) for any similarities. Perhaps we should be insisting that suppliers identify the source of the seed, so that we are not caught unawares. Good Article.

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