If you want to see this in person, check out the spruce in front of Tara's office window at the Administration Building.
Cultivar reversion
Dwarf or variegated cultivars of conifers are often propagated
from sports (mutations). These usually come from a single branch
on a parent plant that has desirable characteristics vastly different
from the parent plant. Such cultivars are often prone to
"reversion", meaning that part or all of the plant reverts to the
form of the parent plant. Dwarf Alberta spruce (Picea glauca
'Conica') is an example. Quite often a branch or section of a dwarf
Alberta spruce (pictured at left) will sprout that has the
characteristics of the non-dwarf parent plant (white spruce, Picea
glauca), which under perfect conditions could reach 40 to 60 feet.
If left on the plant, such reversions will take over, so should be
pruned out as soon as possible. Sometimes reversions can be
triggered by stress.