Trees for the Christmas
Season
Conifers are trees, such as pines, that produce their seeds in
cones. Typically, these plants are evergreen. Conifers are adapted
for survival in cold and dry climates such as is found in Minnesota,
especially during the winter. These plants are designed to minimize
water loss (a major problem for trees in the winter) by possessing
small leaves (needles) with a thick waxy covering (cuticle). Since
the growing season is short, being evergreen gives them a quick start
on growing when conditions become favorable.
Conifers have separate male and female cones that are typically
produced on the same tree (monoecious). Male cones, which produce
the pollen, are usually found on lower branches, and the female cones
on upper branches. It takes two years from the time of pollination
to produce mature seeds. The first year following pollination is
primarily a period during which the female structures prepare for
fertilization and seed development.
Common groups of conifers include:
- Pines (genus Pinus)
The leaves (needles) are produced in
groups (fascicles), the cones have woody scales that don't
disintegrate (are persistent). The cones are not typically produced
at the end of the branches (subterminal).
The most popular Christmas tree is Scotch pine (Pinus
sylvestris). It has needles in groups of two. The needles are
twisted around one another. The young branches have a distinctly
orange colored bark (check out the "swayed pines"). Medium needle
length (1-3 inches), easy to decorate, good needle retention. Native
to Europe.
Another pine sold at Christmas is White pine (Pinus
strobus).
It has needles in clusters of five, they are about 2 inches long and
very soft to the touch. The branches are very delicate and do not
hold ornaments particularly well.
Norway or Red pine (Pinus resinosa) is a full tree with stout
branches and long needles (3-5 inches). Needles in groups of two.
Good needle retention, flocks well. MN state tree. It is a native
tree but got the name "Norway" pine because it reminded the settlers
of the trees back in Europe.
- Spruces (Picea)
The needles arise singly from the twig and
are alternately arranged. The needles are sessile (without a stalk
called a petiole) and leave a woody peg on the twig when they fall
off. The needles are four-angled needles and will roll between your
fingers. The cones are pendant, subterminal (just behind the tip)
and the scales are persistent (in other words, the cone doesn't fall
apart when it is mature).
White spruce (Picea glauca) trees have short needles (1/2 -
3/4 inch long), grayish-green. Poor needle retention. Cones about 2
inches with smooth margins of scales. Native to Canada, NE US.
A beautiful, but somewhat bad-smelling Christmas tree is Blue
spruce (Picea pungens). Its needles are slightly longer than white
spruce (ca 3/4 - 1 inch), very sharp pointed (ouch!), and have a
blue-green color. The cones are 2.5 - 4 inches with ragged margins.
Native to the Rockies, Wyoming to New Mexico.
- Firs (Abies)
The needles are singly attached, alternate,
sessile and leave a large round depression when they are removed.
The cone is upright, subterminal and disintegrates at maturity. They
are slender, spire-like trees with a pointed top.
Frasier fir (Abies fraseri) is the "primo" Christmas tree. It
has dark green needles that are borne is one plane, something like a
feather. There are pronounced white lines beneath and the needles
curve upward. They have excellent needle retention and are very
fragrant. Native to high mountains in Tennessee, North Carolina and
Virginia.
Balsam fir (Abies balsamea), native to eastern North America
and Canada, including Minnesota, has flat needles. Like Fraser fir,
the needles are all in one plane. The needles are dark green and
silvery underneath, though they don't have as distinctive white
lines. Balsam fir has blisters that produce a very fragrant resin
that has been used to seal microscope slides and to produce
turpentine.
- Larch or tamarack (Larix)
Needles occur in clusters at end
of short spur shoots. The needles are deciduous. The cone is
upright, subterminal and has persistent scales. Not used as a
Christmas tree, although Dr. Terry Lilybridge (personal communication) indicates
that it is possible to cut a dormant tamarack a few weeks before Christmas
and then bring it inside and put it in water and it will leaf out in time
for the holiday.
- Douglas fir (Pseudotsuga menzeseii)
Evergreen, with
alternate needles that have a short petiole. The needles are flat
and leave a small round raised scar when they are removed. The
needles are spread all around the twig. The cone is pendant, subterminal and has two bracts that are exerted (looks like a snakes
tongue or mouse ears). It has pointed buds. This tree is native
the Pacific Northwest and Canada. It is an important timber tree and
becoming popular for Christmas trees.
- Hemlock (Tsuga)
Evergreen, with alternate leaves that have a
petiole that leaves a woody "cushion". The cones are terminal
(produced at the end of the branches). Tip of tree waves in breeze.
Not a common Christmas tree in MN.
- Red cedars or junipers (Juniperus)
Group of fairly small
trees and shrubs. Leaves are small and scale-like on young twigs,
sharp pointed on older twigs. Produce a bluish berry-like cone
instead of the typical woody cone. Common Minnesota trees: Eastern
red cedar, Common juniper. These are not used as Christmas trees.
- White cedars or arborvitae (Thuja)
Similar to the juniper
except the branches are flattened, not round. Produce a small woody
cone. These are not used as Christmas trees.
A Key to Species Used Commonly for Christmas Trees.
1a. Needles in bundles.............go to 2
1b. Needles solitary..................go to 4
2a. Needles in groups of 5 ......White pine
2b. Needles in groups of 2.......go to 3
3a. Needles longer than 3 inches....Red pine
3b. Needles 3 inches or shorter......Scotch pine
4a. Needles flat ......................................go to 5
4b. Needles angled, can roll in fingers....go to 7
5a. Buds pointed, needles spiraled around twig like a bottle
brush....Douglas fir
5b. Buds rounded, needles in one plane like a feather....go to 6
6a. Needles very dark green, 2 distinct white lines beneath,
needles curved upward...Fraser fir
6b. Needles dark green, silvery beneath with fainter lines,
needles not curved upward...Balsam fir
7a. Needles very sharp tipped, blue green....Blue spruce
7b. Needles not sharp tipped, green...........White spruce
