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Written by: Tom Stapleton

 Albino redwood scientists consider the Periclinal Chimeric Albino Redwood one of the most intriguing of all redwood mutations.  The reason for the attention is that this particular chimeric subset has yielded the most clues on understanding redwood morphology than any other redwood mutations known to date. It comes as no surprise that Periclinal Chimeras are currently at the heart of albino redwood research. What makes them unique is that they have two genetically distinct cell layers horizontally arced across the top of each redwood bud. This configuration otherwise known as a stratified meristem allows both normal green and mutated cells to divide and elongate at equal rates. In other words, as the apical meristem (tree leader) grows vertically, both layers of each genotype grow upward together at the same rate.  This leads to a very stable, predictable, & long-lived chimera. As each genetic expression forms, scientists have been able to predict with relative accuracy which genotype is likely to occur next in the tree’s branching habit. The Periclinal color scheme has given scientists a virtual road map of how the inner & outer layers are expressed in Redwoods. Interestingly research has shown that all redwood have two genetically distinct layers which before now couldn’t be seen in genotypes with the same color scheme. Unlike Sectorial Chimeras that appear to be two trees sandwiched together, Periclinal Chimeras are literally one tree hidden inside another.

 

 In these green over white periclinal chimeras, the green genotype is expressed first in new growth. Its only later that we see white axillary and accessory buds start forming from the inner layer.

 Despite the stable characteristics of Periclinal Chimeric redwoods, they remain extremely rare in nature. To date, there are only around thirty of these unique Periclinal albino chimeras known to exist in the world. Six of them have grown into full-size trees and are considered 'Grand Chimeras'. The odds of a mutation like this occurring in redwoods are greater than a billion to one!

 

Below are pictures of the six coast redwood grand chimeras known to date. Each tree is listed in order of discovery: 

 

 

1. This is the famous Cotati tree which remains the first occurrence seen of a full-size periclinal albino redwood. Standing at a modest 52.5 feet (16m), the tree exhibits some of the best arrays of color seen with these mutations. This tree was planted in the late 1940s as a normal green redwood. It wasn't until the early 1970's that neighbors started noticing golden-yellow foliage show up in the canopy of the tree. Despite its amazingly color, it took scientists another two decades to discover the tree in 1998. The tree was recently relocated in 2014 to make way for a new light rail project. See the 2014 news section for the story on this tree.

 

2. The second grand chimera to be discovered was the ‘Sac Tree’ which was found in the summer of 2014. For two years it remained as the world’s tallest chimeric albino redwood known until being passed up by tree N#4. This redwood stands in at 82 feet (25m) tall and sports well over 50 mutations. A variegated seedling off this tree can be seen in the 'Projects-Seedling Experiments' section of the website. Chimeric Seedlings

 

 

3. A third grand chimera discovery came in July of 2016. What made this discovery intriguing was that the tree was found in the Willamette Valley of Oregon. With three grand chimeras now found in the urban landscape, a pattern is starting to emerge which shows these mutations tend to favor areas of human development. Influence on our local environments may be a strong indicator of what’s causing these mutations to occur. In the picture above, the redwood is partially obscured by another tree in the right foreground. In the future researchers plan on conducting soil analysis at these sites to determine if pollution may be a contributing factor in causing these mutations.

 

 4. An unbelievable fourth grand chimera discovery was made in the fall of 2016. The tree pictured here is known as the Mendocino Giant Chimera Redwood. To date, this is the tallest & largest chimeric albino redwood known living in the natural redwood range. The tree was measured by Zane Moore in June of 2018 and found to be 110 feet tall. Comparable in size to the Sac Tree, this redwood produces while foliage first, then expresses green in secondary growth which is opposite in color arrangement to what we see with the Cotati & the Sac trees.  Because of the unique phenotypic arrangement (color scheme), a more thorough examination of the foliage will need to be done to better understand this mutation’s patterns. Interestingly, according to the owner, the tree started exhibiting chimeric growth around the year 1975 which is on par with the age of most grand chimeras this size. 

 

 

5. In July of 2017 a fifth grand chimera was found. This tree was also the second one to be discovered in Mendocino county which is noteworthy considering how extremely rare these trees are. This tree located outside the natural range and far from the coast is located in an agricultural area. The tree is comparable in height to the other Mendocino chimera & stands 115' tall and has an approximate DBH of 4.75'. There are approximately 30+ mutations throughout the tree and exhibits similarities like those of the SAC tree. Locals in the area report that nitrogen poisoning was a problem in the past due to over-fertilization of the soil. Whether this is the cause of the mutation remains to be seen.

 

 6. A sixth grand chimera was discovered in October of 2018 in Northern Oregon. What’s remarkable about this tree is that it may be the largest and tallest grand chimera known. Discovered and measured by fellow researcher Brad Buttram, the tree’s diameter was found to be 5.1’ with an estimated height of 129’. The tree exhibits a minimum of 15+ albino mutational growths throughout the canopy and is similar to trees #2 & #5. More of the albino growths appear to be in the upper canopy while the ones that are lower down appear larger in size. This latest discovery is also located in an agricultural setting, provides researchers with more intriguing evidence that human-related causes may be the reason why we are seeing these mutations.

Diagram of a Periclinal Chimera:

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Written by: Tom Stapleton

Mericlinal chimeras are similar to the Sectorial subset with a few distinct differences. Within Mericlinal chimeras, normal or mutated cells do not extend through all layers within the bud or meristem. Usually one genotype (whether green or white) occupies a small portion of the meristem’s outer layers, see diagram. The ratio of one genotype tending to be much larger than the other is characteristic of Mericlinal chimeras. Unfortunately, this causes them to be inherently unstable & short lived. In the wild it’s not unheard of to have a Mericlinal chimera appear in one year & than completely disappear in the next. On some occasions Mericlinal chimeras have been known to successively disappear & reappear again. This is caused by normal or mutated cells growing within the meristem to surface from time to time.

 What’s also interesting about Mericlinal chimeras is they come in two opposite color arrangements: green over white & white over green.

 

 White cells from the inner mutated layer have erupted to the surface on this right lateral bud.

 

In this green over white Mericlinal chimera, notice how short lived the white mutation is. After only a few cm of growth the mutation has completely disappeared.

 

Here we have white over green Mericlinal chimera exhibiting the same characteristics. Only this time the green genotype loses out.

 

This is a rare picture of two needles that are Mericlinal. The needle in the upper portion of the photo barely exhibits the white mutation.

 

 

Diagram of a Mericlinal Chimera:

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Written by: Tom Stapleton

The Sectorial Chimeric Redwood exhibits the showiest color pattern of the three chimeric subsets. Mutated cells extend vertically through all cell layers within the bud or meristem, see fig below. The border between each genotype is almost always parallel within the stem giving sectorial chimeras a candy cane-like appearance. Sometimes both genotypes (colors) are expressed together in individual needles giving them a beautiful split coloration pattern. Because sectorial buds have two different genotypes vertically aligned through the meristem, they tend to be unstable.  In time one genotype will out-compete the other causing the tree to revert either completely green or white. This is why in nature; basal sectorial chimeras rarely exceed 15’ in height.

 

 Here's a Sectorial Chimeric branch exhibiting heterophyllous needles. Notice how the white needles appear shorter than the green. On branches that are split between both phenotypes, you can see the normal green portion of the needle curving around the white causing the tips to look bent.

 

Sectorial Chimeric branch reverting to the white genotype:

 

 A Sectorial Chimera in the wild showing split green and white needles:

 

 A sectorial branch on a greenhouse subject.

 

 Under the microscope, we can see clear lines of delineation between green and white cells on this split needle. The formation of this mosaic pattern in redwoods is a rare yet beautiful oddity.

 

Diagram of a Sectorial Chimera: