Plants & Human Affairs - Introduction

Plants & Human Affairs (BIOL106) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Introduction:
The gymnosperms are a diverse assemblage of plants and are considered to be primitive relative to the flowering plants. Two unique characteristics of this group include: (1) "Naked seeds" (gymno = naked, sperm = seed; Greek), which means that the seeds are not surrounded by a fruit. Rather, the seeds develop on the surface of a cone scale. The flowering plants (angiosperms) also produce seeds from ovules - but these are enclosed in a fruit; and (2) no vessels in their wood. Vessels are large water transporting cells. Gymnosperms have only thinner, tapered cells called tracheids for water transport. Angiosperms have both types.

The most common group of gymnosperms in Minnesota and the predominant one in North America is the conifers. These plants, which includes the pines, spruces and firs, are trees and shrubs that have berry-like or woody cones. Conifers have two types of branches - long shoots (for primary growth - growth in length) and short or spur shoots which bear the leaves. The leaves are needle-like and are typically evergreen. Conifers are monoecious which means they have separate male and female cones on the same plants. They are primarily wind-pollinated.

Most conifers exhibit a variety of adaptations for survival in cold, dry conditions. For example, they have waxy leaves, a well developed layer beneath the epidermis called the hypodermis, sunken stomates, and are evergreen. These adaptations take minimize water loss which is a problem during cold dry winters (or a dry summer season). Evergreen leaves also allow for ready photosynthesis whenever the weather becomes favorable.

Ginkgo (Ginkgo biloba). Another common name for this species is the maidenhair tree which is derived from the fan-shape of the leaves which are reminiscent of those of the maidenhair fern. The tree is commonly cultivated in many temperate areas; in fact, this tree is not known outside of cultivation. It is very tolerant of pollution, drought and cold temperatures (to -30 C) and hence, makes an excellent street tree in cities. The ginkgo was originally known only from the fossil record and probably was at its peak in the Jurassic. It was long cultivated in Chinese temple gardens. It was introduced to Europe in 1730 and then to this country in 1784. The actual name was a typographical error in translating the Chinese characters - it should actually be called the ginkyo. The error was initially made in 1712 by Kaempfer and then formalized by Linnaeus in 1771. The seeds are edible, though the coat has a terrible odor - like rancid butter (butyrate).

Yew (Taxus sp.) These are small trees and shrubs, much branched with persistent leaves persistent that alternate in one plane (2-ranked). The needles have pale green bands beneath or with alternating bands of white and green. The seeds surrounded by a red fleshy tissue called an aril. DO NOT EAT THE SEEDS - they are poisonous! Yew is currently being evaluated as a potential source of chemicals used to treat breast cancer. Taxol is isolated from the bark.

Pines (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 branches. Common Minnesota species include Jack pine (Pinus banksiana ), White pine (P. strobus), Red or Norway pine (P. resinosa), Austrian pine (P. nigra ; this species is very similar to Red pine except that Austrian pine needles don't break with a snap, the buds are usually white and the bark is darker colored); and Scot's pine (P. sylvestris). Mugho pine is a shrubby pine planted as an ornamental.

Spruces (Picea). The needles arise singly from the twig and are alternately arranged. The needles don't have a stalk and leave a woody peg when they fall off. The needles are four-angled and will roll between your fingers. The cones are pendant, subterminal and the scales are persistent. Common species include: Black spruce (P. mariana), White spruce (P. glauca), Norway spruce (P. abies), Colorado blue spruce (P. pungens).

Firs (Abies). The needles are singly attached, alternate, sessile and leave a large, round depression when they are removed. The cone is upright and disintegrates at maturity. They are slender, spire-like trees with a pointed top. Balsam fir (Abies balsamifera) is our native species. Other firs include White fir (A. concolor) and Fraser fir (A. fraseri).

Larch or tamarack (Larix). Needles occur in clusters at the end of short spur shoots. The needles are deciduous (that is, they fall off in the autumn). The cones are relatively small and have persistent scales. These trees are common in wet areas.

Douglas fir (Pseudotsuga menzesii). Evergreen with alternate needles that have a short petiole. The needles leave a small, round, raised scar when they are removed. The cone is pendant, subterminal and has two bracts that are exerted (looks like a snake tongue or mouse ears). This tree is native to the pacific northwest but makes a nice ornamental in Minnesota.

Junipers (Juniperus) - Junipers are shrubs and trees that have evergreen needles that are small and like overlapping scales or are pointed and shaped like and awl. Our common species produce seeds in a berry-like cone. Eastern red cedar (Juniperus virginiana) is a common tree in our area and there are a variety of ornamental ones.

Arborvitae (Thuja) - Arborvitaes have scale-like leaves that occur in pairs. The branches are flattened. These trees are common in northern Minnesota and have been selected in the horticultural trade.