Palmate vs. pinnate

[palmmermaid]

Last weekend I was helping teach a naturalist class and someone asked if all palms really want to be pinnate instead of palmate. We were looking at young Sabal palmettos that have costapalmate leaves which eventually turn into palmate leaves.

Any thoughts or scientific evidence of this? Are the older species palmate and the younger species pinnate?

[Jerry@TreeZoo]

I have thought something similar myself. If you notice that the leaflets of most (all?) pinnate palms except Phoenix are reduplicate instead of induplicate, as all palmate palms are, you wonder if the Phoenix genus is a crossover between the two leaf forms.

[SunnyFl]

I have thought something similar myself. If you notice that the leaflets of most (all?) pinnate palms except Phoenix are reduplicate instead of induplicate, as all palmate palms are, you wonder if the Phoenix genus is a crossover between the two leaf forms.

Amazing idea - what evolutionary advantage would pinnate leaves have? If palms "wanted" to be pinnate, there'd have be an advantage for them....

....maybe help dealing with wind? (Phoenix sp. are outstanding for wind-resistance.)

Also could costapalmate leaves like sabal, and deeply segmented leaves like L. decora also be "crossovers" ?

Edited January 20, 2010 by SunnyFl

[buffy]

Based on the fossil record, the oldest palm fossils appear to be palmate, typically described as Sabalites. I would argue that the existing diversity of palm frond form (palmate, pinnate, bipinnate, etc.) is a reflection of natural selection taking advantage of environmental niches. So, no. I don't believe palms, in general, are moving toward pinnate form, in their evolution. I believe palmate leaves happened to be first, but that doesn't mean the basic design is antiquated. It's like saying monkeys, in general, are evolving towards man. Both man and monkeys are very successful on the planet. And assuming we don't destroy the planet, that success should continue. Just because one group of monkeys evolved into man doesn't mean monkeys, in general, are evolving towards man. There was just a subset of monkeys on the savannah that evolved to be successful in a difficult environment. It just happened to produce a species that could adapt to any environment.

Disclaimer: If you don't believe in Natural Selection, I by no means belittle your position or suggest that you need to see things my way.

[palmmermaid]

Thanks for the responses and thoughts.

I think pinnate fronds are more wind-resistant so maybe the palmate palms haven't evolved into pinnate because there is no need. Sabals are a good cross because they are in a windy environment.

[Alicehunter2000]

I agree with Buffy, adaptations to local conditions would determine leaf structure, much like the needles/leaves on a cactus. This reminds me of a thread awhile back discussing the cold hardiness of palmate palms compaired with pinnate.

I believe most people believe in varying degrees of natural selection, Micro vs Macro-evolution and that this thread would not neccesarily "devolve" into the latter.

[chris.oz]

This is a very good question. Its got me curious.

Just got a copy of GP II , so I will check into it, and my other collection of papers.

Now if JD was lurking on the board these days, I am sure he would have a go at this question !

[palmmermaid]

Chris,

Can't wait to hear what you come up with. It would be nice if JD weighed in!

[Justin]

When I was in the Daintree Rainforest in Queensland (the oldest rainforest on the planet), there were both palmate and pinnate palms. There were huge groves of Licuala ramsayii, which are probably one of the earliest palms. But there were also Normanbyas and Archontophoenix, which are each pinnate.

Part of the issue could be light-related. The Licualas were all in the "secondary" canopy, meaning that they were always getting only a limited amount of light, so a large fan shape would come in handy for grabbing as much sun as possible. Also, they efficiently channeled the water into the heart of the palm when it would rain. Perhaps pinnate palms originally developed in areas where the palms were in the primary canopy, sticking up above everything else. In such an instance, the need for grabbing all the sunlight would be diminished. Also, at the top of the canopy, large fans would probably rip from the wind more commonly, so perhaps the palms slowly adapted by "ripping" naturally - forming pinnate fronds.

[PALM MOD]

I sent an alert to Dr. Dransfield to see if he would be kind enough to weigh in on what I consider and interesting topic. It sounds as if I am not the only one who would appreciate his feedback.

[cfkingfish]

Phoenix is also the only pinnate Coryphoid palm. It is a curious genus indeed.

[sarasota alex]

Based on the information in the GP II the fossil record from the early stages of palm evolution is very incomplete. The age of the oldest known palm leave is about 86 myr (page 75), the age of the oldest pinnate leave is about 76 myr. So it does seem that the palmate came before pinnate. However after looking at the rest of the information in the book, I actually feel that it happened the other way around.

The oldest undisputed fossil palm record, a fruit, is dated at about 112 million years ago (palm pollen dates back to 120 myr, but it sounds like it is disputed whether it's actually a palm pollen). This means that we know of tens of millions of years of palm evolution, without being able to look at what the leaves looked like.

I believe that the common ancestor of all palms had reduplicate pinnate leaves (the most common type today). If you look at the evolution tree of palms on page 98 that would be the parent of Calamoideae and the rest of the palms. The ancestors representing nodes 1, 2 and 3 probably also had reduplicate pinnate leaves, and today so do all members of Nypoideae, Ceroxyloideae and Arecoideae.

A new lineage branched out from node 2 that initially probably evolved to have induplicate pinnate leaves (similar to those of Phoenix). Then costapalmate and palmate leaves evolved (I think in that order) to produce most of the fan palms we know today. At this point I think the genetic code of these palms preserved the evolutionary feature of having pinnate leaves and one of the children of node 3 on page 215 developed an atavistic trait that produced Caryota with induplicate pinnate and bi-pinnate leaves. I also feel that nodes 1, 2, 3 and 4 on page 215 were all costapalmate palms.

It also seems to me that the development of palmate leaves by Mauritiinae is an example of convergent evolution with Coryphoideae.

[John Dransfield]

This really is a very interesting topic and there is no easy clear answer. The fossil record has palmate leaves appearing before pinnate leaves, but the fossil record is notoriously patchy. It does seem to be the case that palmate leaves are more easily preserved in a recognizable state. For example, if you had the tip of the petiole and the base of the blade you could immediately recognise a palmate leaf, whereas fragments of segments could be either pinnate or palmate. The molecular phylogeny and the combined molecular and morphological phylogenies unequivocally provide evidence for the evolution of palmate leaves from pinnate leaves, at least twice, and the evolution of pinnate leaves from palmate twice. Thus Mauritia with a reduplicate palmate leaf arose out of the core of the pinnate leaved Calamoids, and the Coryphoids evolved out of the core pinnate leaved palms. Phoenix evolved out of the core of the Coryphoids (palmate to pinnate) as did the weird Caryotoids). I think these conclusions are pretty robust - as each supplementary line of evidence is added, it seems to confirm these conclusions.

But why palmate and why pinnate? I think there may be some ecological correlations but for every one that you put forward you can find exceptions. Palmate leaved palms are very much features of drier tropics and subtropics and pinnate leaved palms predominate in rain forests - I know, there are lots of exceptions. Perhaps it has something to do with balancing light capture against mechanical stability. But whatever, the basic division - pinnate and palmate - is very robust. A certain amount of modification of these basic types does occur. For example, a few Daemonorops and Calamus have what are to all intents and purposes palmate leaves, having their leaflets crowded at the tip of the petiole, but they are nevertheless clearly derived from pinnate leaves. Phoenix is altogether weird because it has a leaf development completely unlike any other palm, but when you compare it with the distal part of the costapalmate Livistona decora, they do look very similar. In fact it's quite easy to imagine the Phoenix leaf evolving from a costapalmate leaf by extension of the costa (becoming a rachins).

Read what we said about leaves in GP2. If you can get your hands of Barry Tomlinson's wonderful "Structural Biology of Palms" there's lots more about palm leaves and their mechanics.

John

[palmmermaid]

John,

Thanks for all the information. Very interesting and thought provoking. I will pass it along to my students tomorrow and we should have some lively discussions.

I will be on the lookout for the book mentioned.

[jonimic]

Great

I love that topic...

Thanks

[Kathryn]

Kitty - What a great question! I initially ignored this post thinking you were smoking something. If you were a palm, would you rather be pinnate or palmate? This turned out to be a very interesting thread.

[palmmermaid]

Kathryn,

I gave up smoking anything when I had an out of body experience 40 years ago!

It is an interesting question. I never thought about it until last Saturday when the other instructor in my class asked about it.