My wife provided this answer, and she is always right.

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Drzewo okazowe – egzemplarz wyróżniający się wielkością, oryginalnością lub rzadkością występowania, nie objęty ochroną szczególną jako pomnik przyrody.
http://www.bip.muzeum.wloclawek.pl/dworIV/TOM2.pdf/1.01 Proj...

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specimen tree
The definition of a specimen tree varies from gardener to gardener. Some consider especially old trees as specimen trees. Others believe that trees with exceptional beauty are the ones that stand out as specimen trees. Still others will only consider trees that have reached a certain height.

The specimen trees on this page are magnificent. Plant a single specimen tree and it will draw the attention and envy of your neighbors. Before planting, make sure to contact your garden center to see if these beauties will flourish in your area.

http://home.howstuffworks.com/specimen-trees.htm

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Note added at 2 hrs (2016-06-29 11:36:59 GMT)
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spec·i·men plant
noun
noun: specimen tree
an unusual or impressive plant grown as a focus of interest in a garden.

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Specimen Tree
from Code of Virginia (2012)
by The State of Virginia
"Specimen tree" means any tree that has been individually designated by the local governing body to be notable by virtue of its outstanding size and quality for its particular species.

https://definedterm.com/specimen_tree