Gymnosperms - Pinophyta
Four major groups within the gymnosperms are usually recognized - these sometimes each considered its own phylum (Cycadophyta, Ginkgophyta, Gnetophyta, Pinophyta). Here we will consider the gymnosperms to be a natural group and recognize the group as all Pinophyta. For further discussion on each of these four groups, use the links to the Plant Systematics Collection. A smaller group than the cryptogams, the gymnosperms comprise 15 families, 70-80 genera, and about 820 species. The Wisconsin native gymnosperm flora includes 3 families of conifers - Cupressaceae, Taxaceae, and Pinaceae with a total of 8 genera and 13 species. In terms of number of species, not a large group of plants. Like the pteridophytes, many taxa are now extinct, relics of a much larger group.
II. General characteristics
They are woody shrubs, trees or lianas and include no true aquatics and few epiphytes. Of some interest, gymnosperms include the tallest, the most massive, and the longest-living individual plants on earth. They are found throughout much of the earth, but form dominant vegetation in many colder and arctic regions. Familiar ornamentals include pines, spruces, hemlocks, firs, yews and these genera also supply high-quality wood. Like the pteridophytes, many taxa are now extinct, relics of a much larger group.
Gymnosperms possess needles or scale-like leaves, sometimes flat and large, and evergreen! No vessel elements are found in xylem, so out-competed now by vesseled angiosperms except in certain situations. Gymnosperms exhibit cones or strobili, naked seeds (= "gymnosperm"), but not flowers. They are typically slow to reproduce; up to a year may pass between pollination and fertilization, and seed maturation may require 3 years. All gymnosperms are heterosporous and have two types of cones: male, which are smaller and female, which tend to be larger.
Seeds: structure formed by the maturation of the ovule in seed plant; in fact the seeds represent a portion of the life cycle involving 3 generations of plants (mother sporophyte, megagametophyte, and new sporophyte or embryo). Unlike angiosperms (= "encased seeds"), gymnosperms are all grouped together because the seeds are "unprotected" or naked, that is exposed on the surface of bracts. The oldest known seedlike structures are from the late Devonian period around 360 million years ago. Seeds seem to be one of the factors responsible for the dominance of seed plants in today's flora. They have a survival factor the embryo is protected and the stored food that is available is critical and gives them a great selective advantage over free-sporing plants. Disadvantages, when compared to pteridophytes, include (1) expensive to make, so fewer are produced and (2) heavier, so not as easily dispersed.
Water is no longer required for sperm to unite with egg; instead the partly developed male gametophyte (= pollen grain) is transferred to the vicinity of a female gametophyte within the ovule: this is known as pollination. Thus, the loss of flagella on sperm is lost eventually within the gymnosperms. With the exception of the cycads and some gnetophytes, gymnosperms are pollinated by wind.
III. The four Gymnsoperm groups
Palm-like plants found mainly in tropical and subtropical regions. First appeared about 320 million years ago during the Carboniferous; were so numerous during the Mesozoic that is it often called the Age of Cycads and Dinosaurs. Many have a distinct trunk, with the functional leaves at the top - these being large megaphylls, often dissected. Reproduction structures are reduced leaves with sporangia attached loosely or tightly clustered into conelike structures near the apex of the plant. Species are either dioecious (male and female sporangia on different plants) or monoecious (male and female sporangia on same plant). Plants are often toxic with neurotoxins and carcinogenic compounds.
2. ginkgoes: maidenhair tree
One species: Ginkgo biloba; the maidenfern tree no longer living in the wild, and only found in cultivation. The tree was preserved in temple grounds in China and Japan. The genus is known from fossils that date back nearly 200 million years and are nearly identical to present-date trees. It is easily recognized by its fan-shaped leaves and dichotomous pattern of vein; the leaves on the spur shoots are more or less entire, whereas the those on the long shoots and seedlings are deeply lobed. Unlike most of gymnosperms, this is a deciduous tree. The species is dioecious: the ovulate trees produce an abundance of trees which have a particularly obnoxious odor. One of few species of plants known to have sex chromosomes. First brought over to the U.S. from the orient in 1784; it is resistant to air pollution so is commonly cultivated in urban parks. The species is also widely used in the ethnomedicinal trade.
3. gnetophytes: mormon tea, welwitschia, gnetum
Vessel-bearing gymnosperms, but apparently the vessels are convergent with angiosperms. Molecular systematic evidence is suggesting these are closely related if not imbedded in conifers, rather than close to angiosperms as usually assumed. Three families each with a single genus, none of which are found in Wisconsin.
Gnetum: 30 species of trees and climbing vines, with large leathery leaves that resemble dicots
Ephedra or mormon tea with about 35 species, profusely branched shrubs with small scalelike leaves
Welwitschia is one of the most bizarre organisms - most of the plant is buried in sandy soil of the coastal desert of southwestern Africa.The exposed part consists of a massive woody, concave disk that produces only two strap-shaped leaves with the cone bearing branches arising from meristematic tissue on the margin of disk.
4. conifers: pines, spruces and firs
Known from the late Carboniferous, some 290 million years ago. Now dominant only in boreal forests and often found in higher elevations, but as a group they also do well in dry environments. Pines, spruces, and firs are of great commercial value. The tallest (coastal redwood), most massive (giant sequoia), and oldest (bristle cone pine) are members of this group.
All 3 families and 13 species of gymnosperms found in Wisconsin belong to this group:
Cupressaceae - cypress family
25-30 genera around 130 species widespread in temperate regions; fossil record extends back to the Jurassic. Foliage leaves needlelike or scalelike, alternate opposite or whorled, persistent on branches. Cone scale valvate or imbricate; the bract-scales are intimately fused for most of their common length, seeds 1-20 per scale. Heartwood of many species is resistant to termite damages and fungal decay and is widely used in contact with soil. No members of the family attain dominance over immense geographic range, but they can achieve considerable local and regional prominence - eg. redwood forests along the coast of northern California. The cedars belong to this group and wooden pencils are made form incense cedar.
Thuja occidentalis - eastern arborvitae, northern white cedar
Leaves opposite in four ranks. Leaves heteromorphic the leaves on larger branches with sharp erect, free apices to 2 mm; those on flatten lateral branchlets crowded , appressed, scale-like. Small hard cones. Seed cones closed for many years or until opened by fire, scales persistent. Winter deer food.
Juniperus communis subsp. depressa - common juniper, oldfield juniper
Juniperus horizontalis - creeping juniper
Juniperus virginiana - eastern red-cedar
Leaves closely appressed to divergent and scale like; can be dimorphic with scale and awl shaped leaves. Dieocious, sometimes monoecious. The cone fleshy and berry like and remaining closed. Can be used to flavor gin.
Taxaceae - yew family
Taxus canadensis - American yew, ground hemlock
Leaves needlelike and spreading in one plane 2 ranked. No cones, single seed in fleshy aril, but seeds still naked. Heavily browsed by deer. Taxol which is produced from the bark of western yew, T. brevifolia, has been found to be a potent anti-cancer drug.
Pinaceae - pine family
6 genera, around 200 species almost entirely found in the Northern hemisphere; members extend south to West Indies, Central America, Japan, China, Indonesia, the Himalayas, and North Africa. Dominant vegetation of broad regions including forest of the boreal and Pacific. Fossil record extending back to the Cretaceous. Foliage leaves needle-like, alternate or fascicled. Cone scales imbricate and 2 seeds per scale. Major economic importance as world's softwood timber.
Abies balsamea - balsam fir
Twigs basically smooth, there may sometimes be circular leaf scars. Seed cones erect and fall not by cone, but fall scale by scale, each cone axis persisting as an erect "spike" on branch, the fan-shaped scales often littering around the ground under trees. Seeds winged. Heavily scented and used as Christmas trees or distillation of essential oils.
Larix laricina - tamarack, American larch
Leaves in clusters of 10-60. Trees deciduous, short shoots prominent. Species are present in most boreal regions, but often form only a minor component of the vegetation. Wood used sparingly for rough work.
Picea glauca - white spruce
Picea mariana - black spruce
Leaves decurrent and the twigs with roughened by peg-like projections that persist after leaves fall. Leaves sharp-pointed, more or less square in cross section; leaves persisting up to 10 years. Cones pendant on the upper branches, can also appear to be stalked. Often infested with spruce budworm.
Pinus banksiana - jack pine
Pinus resinosa - red pine, Norway pine
Pinus strobus - eastern white pine
Dominate broad stretches of North America and Eurasia. Leaves singly or in clusters of 1-2-5. Branches long and short shoots. Cones protect ovules and seeds; consist of an axis bearing highly modified short shoots, the ovuliferous scales. These scales are subtended by bracts, which are either large and conspicuous. Three species in Wisconsin show varying degrees of tolerance to moisture stress, and thus fire.
Tsuga canadensis - eastern hemlock
Leaves smaller and decurrent and the twigs with roughened by peg-like projections that persist after leaves fall. Leaves rounded or notched at tip, flattened. Branches horizontal, often tending to be arranged in flattened sprays and arched downward, no short shoots. Are found naturally in areas of relatively moist climates where water stresses are minimal.