Two Trees in One? Good or Bad?

In a recent cemetery walk, I noticed a Japanese Maple that appeared to be two different plants. In actuality, there are two varieties in one.

 

The reality is it was 2 different varieties of Japanese Maple. The question… Where is the Graft Union?

 

The original Japanese Maple that was variegated, was potentially Acer palmatum ‘Butterfly’ or Acer palmatum ‘Orido Nishiki.’

 

Typically, these Japanese Maples with variegation are grafted on a straight Acer palmatum rootstock.

  

As the tree grows, sometime a sprout below the graft union may emerge. Unfortunately, the root system which is a straight Japanese Maple variety will be more vigorous and outgrow the grafted tree that is more desirable.

 

The solution is to remove the suckering branch below the graft union.

 

These suckers may reoccur from time to time and can be easily removed when small as they reappear.

 

If the homeowner does nothing, the tree below the graft union will probably outgrow the preferred grafted tree which may eventually die.

 

The horticultural term for this is ‘Reversion.’

 

Other plants can revert to plants below the rootstock. Or sometimes plants will revert from the center of a sport on evergreens.

 

Spring flowering is a great time to see examples of plants that have suckers below the graft union. Peak flowering in Northern Ohio reveals some curious plants the seem to have different color flowers on the same tree. What’s happening? One word……..Reversion?

 

Actually, there are 2 different plants genus species and possible cultivars growing on the same plant.

 

The flowering reveals that the plant is actually 2 different plants on the same rootstock. Many times, plants that are grafted will have growth that occurs below the graft union. The plant below the graft union is the rootstock of the plant that was grafted on top. Why not just grow the plant on top by using cuttings. Many will not root. In order to grow the cultivar, it has to be from the original sport or parent plant.

 

Regarding evergreens, all Dwarf Alberta Spruce, Picea glauca ‘Conica,’ originated from the same plant.

 

In this case, the Dwarf Alberta Spruce is reverting back to White Spruce. Dwarf Alberta Spruce, Picea glauca ‘Conica’ is reverting back to straight White Spruce, Picea glauca.

 

In another case, this sport of this Juniper is reverting back to the straight species which has a more open growth habit as opposed to the cultivar which has a more compact growth habit.

 

Dr. Curtis Young and Beth Scheckelhoff wrote a great article on why this occurs:

 

Quoting them: “Botanists and gardeners have long marveled at Mother Nature’s ability to randomly produce unique plant, foliage, and flower forms, colors, and growth habits from common plants.

 

Many variegated plants have arisen from a genetic mutation within the parent plant, often called a “sport.” This variegated portion of the plant can be removed and propagated as an entirely new cultivar (cultivated variety) from the parent. It is important to remember that the sport must be propagated by vegetative means – divisions, cuttings, tissue culture, etc. - to maintain these distinct characteristics. These plants will not come true from seed that is grown, although seedlings may produce equally interesting progeny.

 

Another unique source of dwarf conifers is the phenomena of witches’ broom. A plant with witches’ broom develops growth featuring highly congested shoots with shortened internodes – hence appearing like twigs bundled into a witch’s broom. These brooms can be found on a wide variety of tree and shrub species and can be caused by genetic mutations, but more commonly from insects or disease infestations. Only those developed from a genetic mutation can be propagated by vegetative means to maintain the mutation. Growing out the seedlings of these mutated plants can also yield progeny with varying degrees of dwarfism. For more reading on the subject – see this 1967 article from the Arnold Arboretum on “Dwarf Conifers from Witches’-Brooms”.

 

Link is found here: https://arboretum.harvard.edu/arnoldia/arnoldia-search/?q=witches+broom

  

The complete article by Curtis and Beth is found here: https://bygl.osu.edu/node/1602

 

The goal of propagators is to find a stable sport that will retain its ornamental qualities.

 

Several great examples are Globe Blue Spruce, Picea pungens glauca ‘Globosa’

  

And Bird’s Nest Spruce, Picea abies ‘Nidiformis.’

 

Plants don’t always follow the rules. Reversion is always a possibility, genetically speaking.