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Wednesday - April 11, 2007

From: austin, TX
Region: Southwest
Topic: Trees
Title: Variegated leaves on Ungnadia speciosa (Mexican buckeye)
Answered by: Nan Hampton

QUESTION:

I grew some mexican buckeyes from seed last year and one of them has variegated leaves. I haven't seen this before- have I just not looked at enough mexican buckeyes up close or is this an uncommon finding?

ANSWER:

No one I've talked with here at the Wildflower Center has ever seen a Ungnadia speciosa (Mexican buckeye) with variegated leaves, so I guess we can say it is rather rare occurrence.

Variegation, with white sectors in the green leaves, occurs when the chloroplasts (the photosynthetic apparatus in the cells of plants) lose their ability to make chlorophyll. This can occur when the DNA of the chloroplast is mutated. Cells of plants have from several to many chloroplasts per cell. Chloroplasts themselves reproduce inside the cells by simple division, so once a mutation occurs in a chloroplast it will be copied. As the number of mutated chloroplasts increase inside a cell, the chances of a dividing cell isolating only mutated chloroplasts in one of its daughter cells also increases. As the cells divide, those that receive only the mutated chloroplasts (and no normal chloroplasts) will be white. These cells with only mutated chloroplasts will divide to form more white cells without normal chloroplasts. On the other hand, cells that have at least one normal chloroplast will be green. This is how the variegation occurs.

These white sectors without chlorophyll are not capable of carrying out photosynthesis to supply the plant with nutrients; therefore, highly variegated plants with a lot of white sectors tend to be smaller and weaker plants since only the green areas are producing the energy to allow the plant to grow.

Some plants exhibit other variegation patterns with red, purple, and yellow sectors. In this case, other pigments are masking the green of the chlorophyll and photosynthesis still occurs in those sectors.

Back to the rarity of a variegated Mexican buckeye, the reason it is relatively rare is probably a combination of the fact that the mutation rate is low and the chances of isolating only mutated chloroplasts in cell are also low, plus the fact that variegated plants are at a disadvantage for competing with normal plants.

You can read more about variegated leaves and plant variegation.