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According to the Sept. 16, 2007, New York Times, while Ken Burns was previewing the Grand Canyon segment of his upcoming (2009) series on national Parks, he heard a reference to deciduous trees but presumably saw evergreens. He commented, “I don’t mean to nitpick…”those are not leaves, they are needles.”
Here’s a botany lesson for Mr. Burns. Needles are leaves. They are just very narrow and scale-like. Even prickly cactus thorns are leaves. Christmas tree needles that burrow into rugs are leaves.
Evergreens have leaves all year round; they just lose them gradually, from the inside out. Like other leaves, needles photosynthesize, using sunlight to turn water and carbon dioxide into the sugars that fuel the tree. Needles live for one to several years, depending on the species of tree.
Needles have adapted to retain water in extreme climates. They have a very small surface area and a waxy coating permeated by tiny openings through which gases pass in and out to keep cells functioning. Because they retain chlorophyll year round, they can photosynthesize at any sunny opportunity.
Trees with needles are gymnosperms, with naked nut-like seeds that do not grow within the protection of an ovary. Seeds are usually produced within cones, hence the name conifers.
A “berry” on an evergreen is really a modified cone, properly called an “aril.” All conifers are wind-pollinated.
Evanston’s only possible evergreen was a beach-hugging juniper, still alive and well at Illinois Beach State Park. Evergreen conifers are no longer planted on our parkways because they obstruct sight lines and may be susceptible to salt spray. Several families of evergreens are planted in our parks.
Two species represent the Cypress family: white cedar or Arborvitae, and Eastern red cedar. Both are typical ornamental foundation plants native to the United States and have reddish brown, stringy bark.
Arborvitae (Thuja occidentalis, meaning “of the west”), is also called “tree of life” because of its countless medicinal uses. In the 16th century American natives taught Europeans to chew the vitamin C-rich leaves to ward off scurvy. Thuja is Latin for cedar, an aromatic wood often burned as incense during ancient sacrifices. Arborvitae’s scale-like leaves grow on flattened, overlapping branches. Some trees produce tiny cones. These skinny, pointy trees are often planted in rows as living privacy fences.
Eastern red cedar (Juniperus virginiana), or pencil cedar, is native to the eastern United States It has feathery soft leaves and sharp, prickly leaves on the same tree. It is used in perfumes, pencils, fence posts (because its heartwood is rot resistant), and cedar closets (because its oil repels moths). Its light blue berrylike arils are produced by female trees and have been used for flavorings. Tall red cedars provide refuge for wintering birds on Independence Knoll in Ladd Arboretum.
Japanese Yew (Taxus cuspidata), in the family Taxaceae, is a slow-growing Asian native. Its flat leaves grow alternately on three sides of the stem. The red fruit is an aril. The entire bush is toxic in some manner to humans and animals, especially children, dogs, cattle and horses. Deer, however, can browse it down to the point of killing the tree with no ill effects to themselves. It all depends on the creature’s digestive system. Very few Japanese yews, really overgrown shrubs, grow on our parkways.
Four species of pines (Pinus in the Pinaceae family) grow on our public land. Their round, thin needles grow in bundles wrapped in short sheaths at the base.
The white pine (P. strobus, Latin for pine cone) is native to our region. Its almost white wood, much desired for building and boat masts, provides its common name. This lovely tree has soft, five-needle bundles. A row of white pines grows at the south end of Lighthouse Beach.
Three pines growing in Evanston have two-needle bundles. The Austrian pine (P.nigra, meaning black), is so named because of its dark crown. It is native to central and southern Europe and Asia Minor and thrives in urban conditions. Its dark green, heavy needles have rough sheaths and bend easily.
The red pine (P. resinosa for its generous amount of resin, which protects against bugs), is native to northeastern North America. Red pine needles snap when bent. Their reddish scaly bark explains their common name. Austrian and red pines grow in Ladd Arboretum and are so similar that identification is challenging.
The Scotch pine (P. sylvestris, from the Latin sylva, “of the woods”) is another import, native to Scotland and Spain across Eurasia to Siberia. This favorite Christmas tree has become so susceptible to a variety of diseases that my Christmas-tree farmer friends no longer plant them. A group of Scotch pines grows near the pond at Lovelace Park. Their strong, bare curving orange branches make them easy to identify.
Spruce trees are also in the family Pinaceae. The genus name, Picea, refers to the pitch in almost all spruce species. The Norway spruce (P. abies), is native to northern and central Europe and is the fastest growing spruce. It can top 120 feet and grow to 40 feet wide. No wonder it is the official Christmas tree of New York’s Rockefeller Center. Its dark green needles are about an inch long, its cones about six inches. As the tree matures, its main branches turn up at the tips, but long branchlets growing along the limb give it a droopy appearance. A Norway spruce grove grows near Emerson Street in Ladd Arboretum.
The lovely Colorado spruce (P. pungens) is native to higher elevations in the Western United States. The needles grow individually all around the twig. Pungens refers to their spiky ends. When growing in acidic soil, the silver-blue color of their leaves is stunning. A picture – perfect display of young blue spruce decorates the south side of Leider park, at the corner of South Boulevard and Asbury, in the Ridgeville Park District. South of the Levy Center, a group of mature blue spruce appear majestic against a backdrop of white snow.