Why leaves turn red?

[Palm Guy]

I've been trying to understand why palm leaves turn red. After searching some websites I found and talking with some of the forum members I've heard two possible trains of thoughts.

1. Redder in cooler weather

2. Red is a defense mechanism that acts as a sunscreen

A theory I thought of (may have been someone else's idea) would a combination of the two.

3. changes of leaf color to the amount of sunlight present. Less sunlight is generally common in cooler weather.

Many trees in fall change color as a response to the amount of daylight. Pointsettia plants are 'forced' into flower by placing them in dark rooms with no light for a period of time.

When you think about it, most palm species like Chambeyronia look redder in shade. They usually start off in the understory and move towards the top of the canopy. The spear that starts within the crownshaft is not exposed to much light at all. When it slowly begins to open it gets exposed to more sunlight and the leaf then turns green due to the chorolphyll gained by exposure to sunlight.

Same can be applied to Kentiopsis magnifica which generally starts off in the shade and is known to lose its red feature as it begins to be exposed to more sun or as it ages.

In fact, most palm species with a red feature either start in shade or live in shade all their lives. I might be making generalizations but I want your opinions and feedback.

Cheers,

[Brad-Tampa]

I think the color is always there, the green clorophyll develops and masks it. Why there is more in some specimens I have no idea, maybe a mix of genetics and enviornment.

[Daryl]

I have also read somewhere that it may be a defence mechanism against animals and insects as the red appears to be brown and looks like dead foliage, thereby not treated as a tasty meal. No New Caledonian palm has spines or thorns, but quite a few have red new leaves.

Daryl

[bgl]

Michael,

I don't have any answers, but like Brad said, I'm sure the color is always there. In other words, the fronds don't turn red. They're ALREADY red and THEN they turn green!

Bo-Göran

[Palm Guy]

Good point, I'm sure thats what I meant to say but its definitely not what was written in my post. Moderator, help! I agree with Brad too in that the color is always there. Its the sunlight that makes it turn green and the lack of that makes them come up red. I wonder how long a red leaf would last on a palm held in complete darkness, thats before the palm dies of course.

[Palm Guy]

I have also read somewhere that it may be a defence mechanism against animals and insects as the red appears to be brown and looks like dead foliage, thereby not treated as a tasty meal. No New Caledonian palm has spines or thorns, but quite a few have red new leaves.

Thats a good point too Daryl. The opposite could be true also as the red may attract pollinators. So many possibilities!

[DoomsDave]

(bgl @ Feb. 08 2008,18:12)

QUOTE

Michael,

I don't have any answers, but like Brad said, I'm sure the color is always there. In other words, the fronds don't turn red. They're ALREADY red and THEN they turn green!

Bo-Göran

They're actually visibly red, then turn visibly green . . . .

[cryptobionic]

Anthocyanins, the flavinoids responsible for red and purple pigmentation in plants parts are used to attact pollinators in flowers. When present in foilage, they serve as a sunscreen for very young and very old leaves, and can intensify with cooler temps in combination with UV. Another purpose is that it serves as a warning of unpalability or toxicity (yet most times only in appearance) of leaves, while some herbivores are blind to the color red (it appears as brown or grey), and so ignore red-tinted foilage. I'm sure there's tons of recent findings related to the purpose of anthocyanins; Kevin Gould wrote a paper on anthocyanins and palms, but I'm far too lazy to look it up.

[Palm Guy]

The only thing I don't get with the sunscreen theory is that the leaves tend to appear more red in shadier/less UV/cooler environments? Shouldn't it be more red in the sun if it were to act as an effective sunscreen? I can see the theory making sense in the case of a palm being surrounded by trees and if there was a sudden break in the canopy it would need lots of "sunscreen" to cope with the sudden change in UV.

[kakariki]

There was an article in a local geographic magazine a month or two ago which was strongly in favour of the anthocyanins as defence mechanism against chewing and sucking pests. Have a look here: NZ Geographic Archives, Issue 60.

While you are there in issue 65 is an article on Nikau. If I've got it right this should get you there: NZ Geographic Archives, Issue 65

[MASOALA JASON]

I agree with Palm Guy; in this case, it seems selection for an increase in anthocyanins is not the result of an adaptation to more exposure to UV light, but as an adaptation to herbivory. The anthocyanins are suggested to act both as behavioral deterrents-the color warns of possible toxic phenols-and as a physical deterrent; it is suggested animals view the relection of the red light wavelength as brown and might avoid senescent or dead foliage, as was stated in previous posts. The anatomy manifested by an individual or population of specific palms is the result of some innovation in regard to its environment at some specific point in time. Whether the animals that might have elicited this adaptation,which probably arose independently in different palm groups, still exist does not negate the fact the trait was useful at some point in the palms evolutionary history.

[kellana]

 have 2 palms next to each other one with leaves turning red/orange, hoping this is natural and it's not sick.

[kellana]

just noticed 14 years later... is there anyone in there or just a sad echo of the past...

[tim_brissy_13]

3 hours ago, kellana said:

just noticed 14 years later... is there anyone in there or just a sad echo of the past...

The palms are Phoenix canariensis. The one on the right with the red/orange colour is a female and the colour is the flowers and fruit. Completely normal.