Those dratted orchid name changes

[Dorsetman]

Whilst we have been in our greenhouses, whingeing on about name changes, and having to turn Odonts into Oncids, etc, out in the big wide world of non-orchids, even greater revolutions have been taking place it seems.

Did you know ( how could you have dreamt ?) that Sycamore and Horse Chestnut were closely related ? Now, it seems, Acer and Hippocastanacaea don’t exist any more ; the family now concerned is Sapindaceae - of course you knew that Lychees and Rambutan ( another tropical fruit which you may not have met unless you have been to/lived in the Far East ) are typical examples of that genus.

Actually I still find that a bit hard to swallow, whatever the DNA says – I suspect it is a hiccup , someone turned over two pages instead of one. Rambutan and Lychee and Horse Chestnut I will believe, all have knobbly if not prickly large near-spherical “seeds” i.e. fruits ( not that I would like to eat a conker ; for the benefit of all my friends around the Pacific, the conker is a hard-as-stone fruit of the Horse Chestnut tree, and is used by English schoolboys to play a game, of the same name). But the Sycamore has that familiar winged and merely fibrous coated pea-sized seed .

Personally I only think of Sycamores and also the more ornamental Acers, such as A.palmatum, in the genus , but it is so large and important that one of the divisions (types) of forest in Thailand is called Dipterous – meaning trees which have two-winged fruits (Acer being the one which comes to my mind).

Of course, if I utter it out loud , (that I don’t believe it ) I will be told that this is the whole point – the new botany is based on DNA similarity, not similarity of physical shape ( morphology) .

Foxgloves and Mallows, Scilla and Chionodoxa – all have changed their names – and I’m only mentioning the ones imporrtant in temperate region gardens, which also happen to have been the ones I read out about today , in an interesting piece in a British newspaper (The Telegraph) gardening section.

Clearly there is no end to the name changes ; we must stop feeling hard-done by as orchidists – all serious plant cultivators are in the same boat. .

Throw away all your gardening books . They are all out of date. I think it’s a conspiracy by the publishers, to sell new editions. Someone must be busy writing them ! Who ? Why the DNA merchants of course ; it’s all a plot.

[pavel]

Personally I think it is a ploy by the taxonomists to create their own job security.

[Gin]

Personally I think it is a ploy by the taxonomists to create their own job security.

I think you are right nothing to do, so let's confuse the plant lovers . I don't know what I have if I read the names they come up with .

[Brutal_Dreamer]

So much to learn each time a change occurs. I finally gave up on it. I keep my tags as they are and look up any orchid I want to show before to make sure I have the name correct.

Cheers,
BD

[BearWithMe]

As a novice it's all really confusing to me. I always wonder how inter-generics can be fertile, since I thought that the point of being a different genus is they couldn't reproduce together. Beats me. Then the intergenerics have their own genus names.... So then we rename and regroup the genera, so the intergeneric names change too, in some cases, but not in other cases.... arrgh! I suppose that if taxonomy is to have meaning, it needs to be based on DNA, so I just need to keep learning.

[Dorsetman]

As a novice it's all really confusing to me. I always wonder how inter-generics can be fertile, since I thought that the point of being a different genus is they couldn't reproduce together. Beats me. Then the intergenerics have their own genus names.... So then we rename and regroup the genera, so the intergeneric names change too, in some cases, but not in other cases.... arrgh! I suppose that if taxonomy is to have meaning, it needs to be based on DNA, so I just need to keep learning.

It seems to me that in theory, if you can get the chromosomes from the two parents into the same cell ( the ovum) there is a possibility that they will combine before the first meiosis occurs. Whether that makes a viable embryo is another matter . But “way out” pollen does not fertilise the seed parent in most cases for other reasons – the gamete never gets to the right place, never even starts its journey. To do that the pollen must interact with the stigmatic surface to produce the correct protein sequence to allow or perhaps cause growth of the pollen tube, along which the gamete has to travel to reach the seed. The comparison is with keys and locks. Every stigmatic surface is a lock ; every grain of pollen is a key. But does the key fit the lock ? Or is it near enough to make the lock open sometimes – in which case poor seed production may result – although even then- there must be some kind of match of the chromosomes. Not precisely as shown by Paph hybrids, which can have all kinds of different chromosome numbers – I have heard of 22, 24, 27, even 42 chromosomes – but paphs will breed together despite this mismatch.

It would be nice to be 18 again, and study genetics this time – hey, it would be nice to be 18 again, period.

[catttan]

Personally I think it is a ploy by the taxonomists to create their own job security.

I agree. How else can they justify the funding.

[pavel]

As a novice it's all really confusing to me. I always wonder how inter-generics can be fertile, since I thought that the point of being a different genus is they couldn't reproduce together.

HUSH MAN, HUSH! Don't give those darned taxonomists any more ideas! No telling what chaos they'll unleash.

It seems to me that in theory, if you can get the chromosomes from the two parents into the same cell ( the ovum) there is a possibility that they will combine before the first meiosis occurs. Whether that makes a viable embryo is another matter . But “way out” pollen does not fertilise the seed parent in most cases for other reasons – the gamete never gets to the right place, never even starts its journey. To do that the pollen must interact with the stigmatic surface to produce the correct protein sequence to allow or perhaps cause growth of the pollen tube, along which the gamete has to travel to reach the seed. The comparison is with keys and locks. Every stigmatic surface is a lock ; every grain of pollen is a key. But does the key fit the lock ? Or is it near enough to make the lock open sometimes – in which case poor seed production may result – although even then- there must be some kind of match of the chromosomes. Not precisely as shown by Paph hybrids, which can have all kinds of different chromosome numbers – I have heard of 22, 24, 27, even 42 chromosomes – but paphs will breed together despite this mismatch.

It would be nice to be 18 again, and study genetics this time – hey, it would be nice to be 18 again, period.

Well here we go. To those who find this next part the pinnacle of boredom --ranking somewhere between the rollicking good fun of watching grass grow and trimming ones toenails -- I apologize in advance for boring the socks off of you.

In a simpler world, your current understanding, Daniel, would be quite correct. Unfortunately (or fortunately, depending upon one's point of view), life is rarely simple.

Even amongst animals. the lines between genera though fairly well delineated are not necessarily written in stone -- and between species even less so. But generally speaking, the greater the complexity of the organism, the less forgiving nature is with alterations to the DNA template or attempts to combine disparate sets of DNA. For this reason, barring the possibilities proffered by genetic engineering, it is not possible to cross a horse and a cow (which differ at the Family level) to obtain viable offspring. A cross between bison and cattle (which differ at the Tribe level -- a taxonomical level between Family and Genus) is possible but offspring are rare and sterile. [And even then the cross is believed to only be possible because of how closely related those two particular genera happen to be.] Crosses between species, because of their high degree of relatedness, are more likely to produce viable, fertile offspring. Yet even at this level, offspring are often sterile and crosses rarely happen in nature.

Lacking as high degree of complexity as that found in animals, plants' genomes are more forgiving of odd crosses and combinations. However, there are still very real limits and crosses among genera may display decreased fecundy in many cases -- particularly if the genera in question are far apart on the family tree.

So despite this, why don't we see more trans-generic crosses in nature?

In many cases it is due to geographical isolation. If two groups of organisms are prevented from interacting due to some environmental barrier, they are prevented from cross breeding.

Behavioral differences also prevents many organisms from commingling. A bird whose call or body language does not match what another recognizes as being that of a potential mate will not do so. A plant that only blooms in the spring or elicits response "X" from a pollinator will not be pollinated by another plant that blooms in the fall or if it fails to trigger that same response from that pollinator.

Then there are morphological and physiological differences to prevent cross breeding. Geoff mentioned a 'lock and key' arrangement. An apt metaphor. Spiders are by and large unable to crossbreed. Each species has a lock and key system in which the male sexual apparatus can only fit into the female orafice of his own species (this is on top of necessary behavioral cues needed for like-specie recognition). Such differences also exist in the plant world. Many orchids have designs to their flowers that cause a specific pollinator to take a certain route to reach the nectar or to escape from the flower such as in paphs or Coryanthes. In addition, Geoff is also quite correct that pollen requires certain chemical compounds in order for the pollen tube to grow and reach the ovary. Not all plants use the same set of chemical compounds to achieve this.

Under any of these circumstances, if two populations are 'isolated' long enough, it is possible that genetic drift/separation can occur. Once enough differences have accumulated, no cross breeding is possible. But it should be noted, that even if they do not genetically diverge to the point of being genetically incompatible, if two populations do not interbreed due to those reasons mentioned above, they will still be considered separate species. Mankind, meddlers that we are, can create circumstances that induce species to mingle their DNA when they normally would not. At times, this results in new desirable (in our eyes) hybrids.

I now return you to your regularly scheduled thread.

[BearWithMe]

Thank you Pavel. Now I'm going to work on my tomato-dendrobium hybrid so I can have my orchid and eat it too. :-)

[Halloamey]

Please don´t curse us plant molecular biologists LOL. I am myself a part of a project where we are working on the brassicales family (the one to which mustard, cabbage, broccoli etc belong) we are trying to find out the relatedness and differences in a particular gene which can help us in deciding the heirarchy. Its all DNA genomic evidence is the final on (atleast now). Phenotype or morphological similarities can be due to homoplasy, i.e. similar looking organs due to a similar need like the fins of a fish and a dolphin, but both have arisen independently.