Gymnosperms

Gymnosperms and Angiosperms

Gymnosperms are a group of woody, perennial, seed bearing plants which first came into being 300 to 350 million years ago, millions of years before our other seed bearing plants, the angiosperms, or flowering plants. Gymnosperms and angiosperms are both seed bearing, but come from separate lineages and fertilize, protect and disperse their seeds differently.

In angiosperms, the reproductive organs are housed in flowers which are designed to attract bird and insect pollinators by producing vibrant colors, scents and nectar. Flowers may be unisexual, with male and female reproductive organs on separate flowers, or bisexual with both the male and female organs in the same flower. Fertilization occurs in an ovary producing a seed which remains enclosed and protected in the ovary which often grows into a fruit. Seeds are then dispersed by either pollinators or wind.

In gymnosperms, which come from a more ancient lineage, the process is somewhat simpler. Gymnosperm reproductive organs are borne in cones or on scales or leaves. In Colorado, our native gymnosperms are all cone bearing plants. They do not contain any of the angiosperm characteristics designed to attract pollinators. The seeds are “naked” meaning that they are not surrounded by an ovary. The cones are all unisexual and the seeds are all dispersed by wind. However, some larger seeds, which fall to the ground may be dispersed by squirrels or birds.

Reflecting their later and more advanced evolution, angiosperms plants express themselves in different forms, annuals, biennials and perennials and as herbs, shrubs and trees. They occur in all but the most extreme aquatic to terrestrial habitats and are clearly the most dominant seed bearing plants with an estimated 250,000 to 400,000 species present today. In their heyday, before angiosperms started evolving 200 to 250 million years ago, gymnosperms were the dominant seed bearing plans but they only had a few thousand species with only about 1,000 species surviving until today.

The final primary difference between angiosperms and gymnosperms are found in the leaves. Gymnosperms generally have small, thin needle- or scale-like evergreen leaves, which help them conserve water in harsh environments. Angiosperm leaves are broader and flatter and are more often deciduous than evergreen.

Today, in Colorado, our gymnosperms are limited to woody perennial, evergreen trees and shrubs with only eighteen species in three families. However, they are the dominant indicator species in our forests in montane and subalpine zones where the weather is more extreme and the soils more acid and nutrient poor. They are also found in rocky areas in lower elevations and in deserts.

The Pine Family (Pinaceae)

Of the three gymnosperm families in Colorado, the pine family, is the largest. Worldwide there are 11 genera with 220 species, but in Colorado we only have eleven species in four genera. Here all pines are evergreen trees which form the backbone of Colorado forests in the foothill, montane and subalpine life zones. Pines have linear needle-like leaves which are spirally arranged around the stem. The needles may grow singly on the stem or grow in clusters of 2 to 5 held together at the base by a membrane called a fascicle.

As with all of the gymnosperms, the male and female organs appear on separate cones. The male cones are small and disperse their pollen into the wind, dropping off the tree immediately after pollination is complete. In spring one can often see clouds of pollen in the air, so much of it is produced. The female cones are larger and become elongated, exposing their ovules to the pollen in the air. Once the ovules come in contact with the pollen, the cones grow scales, covering and protecting the ovules, which then grow into seeds. Once matured the small, lightweight, winged seeds are dispersed by the wind.

In the Abies (Fir) genus we have two species of trees. Both have needles which grow singly, and can be used to identify the genus by the fact that they are flat, and do not roll between your fingers. Their cones grow erect on the tree. Rocky Mountain Subalpine Fir (Abies lasiocarpa var. bifolia), grows in the montane and subalpine zones, from 7,800 to 12,500 feet, often with Englemann Spruce (Picea englemannii). The second species is White Fir (Abies concolor), which is found primarily in the southern counties of Colorado in slightly lower elevations from 7,500 to 11.000 feet.

The common name for the Pseudotsuga genus is Douglas Fir, but the single species found in Colorado, Pseudotsuga menziesii (also Douglas Fir) is not a true fir, as in the Abies genus. It is differentiated from true firs by the fact that its cones have three-pointed bracts which extend out between the cone scales. Another difference is that the cones hang down from the branches rather than standing erect as in Abies. Finally, like Abies, Douglas Firs have flat, soft needles, but they are attached to the stem in a manner that leaves a small rounded leaf scar when they fall off. In Abies, when the leaves fall off they do not leave a leaf scar. Douglas Firs grow to 50 meters tall in Colorado and are a dominant component of montane and subalpine forests, often growing with white fir (Abies concolor) and spruce species.

In the spruce genus (Picea) there are also two species. Like the firs, they have single needles that are spirally arranged around the stem, but the needles are not flat but square and can be rolled in between your fingers. Their cones are not erect but pendulous or spreading. Englemann Spruce, as noted above, often grows with Subalpine Fir in the montane and subalpine zones from 7,800 to 12,500 feet. Colorado Blue Spruce (Picea pungens) is mostly found at elevations in the foothills, from 7,000 feet into the montane at 9,500 feet, but occasionally can be found in the subalpine up to 11,000 feet.

The Pine genus (Pinus) is the largest genus in this family, with six species. All of the pines have longer leaves than the firs or spruce (greater than 2.5 cm long), and all of them come in clusters of 2 – 5 leaves held together at the base by fascicles. Pinyon Pine (Pinus edulis) can grow as a shrub or tree up to 20 meters tall and has leaves 2-4 cm long in bundles of two. It grows at the lowest elevation on dry slopes, mesas and canyons, often with junipers from the plains to the foothills.

In slightly higher elevations from canyons up into the foothills (4,000 to 9,500’) you will find Ponderosa Pines (Pinus ponderosa). Ponderosa pines have the longest needles (10-20 cm long) in our pine family and they occur in bundles of 2 or 3 per fascicle. Take a whiff of the bark, which smells like butterscotch or vanilla. Ponderosa pines have evolved to be resistant to low-intensity fires by the presence of their thick bark.

Limbur Pine (Pinus flexilis) often likes to grow in rocky crevices in montane and subalpine forests up to 12,000 feet, but a relictual population exists at a place called Dave’s Draw in the Pawnee National Grasslands at an elevation of 5,300’. Limbur Pine has 3-5 cm long leaves in bundles of five and grows to 26 meters tall.

Lodgepole Pine (Pinus contorta) is our dominant tree in montane forests (7,500 – 11,600’), with leaves 3-7 cm long in bundles of two. As with ponderosa pines, it is also adapted to fire, but not because of it’s thick bark, but by its serotinous cones. These cones remain closed and hold on to their seeds until they come into contact with fire. The fire melts the resin holding the cones closed, releasing the seeds into the nutrient rich soil resulting from a fire. Stand replacing fires often result in dense monocultures of lodgepole pines.

Bristlecone Pine (Pinus aristata) is the grand daddy of our subalpine forest. It’s population reaches its northern extent in Grand County, Colorado. It’s leaves are 3-4 cm long in bundles of 5, and it is easily identified because its leaves are covered in drops of resin, which help to maintain moisture. Bristlecones are one of the oldest living organisms on earth. In Colorado, a bristlecone pine in South Park has been dated to 2,500 years old.

And finally, Southwestern White Pine (Pinus strobiformis) is found in the southwest corner of Colorado, reaching its northern extent in Park County. Its leaves are 4-9 cm long in bundles of 5. it grows in montane and subalpine forests from 6,000 to 11,000 feet.

The Cypress Family (Cupressaceae)

The second of three plant families in our Colorado gymnosperms is the cypress or cedar family (Cupressaceae). It is a much smaller family here with just one genus, Juniperus, and four species. Whereas the pine family first appeared about 300 million years ago during the Carboniferous period, the cypress family appeared, much later, about 200 million years ago during the Triassic period.

Our Common Juniper in Colorado (Juniperus communis) is a low or spreading shrub growing up to 3 meters tall. It is the only one of our species which has needles, one half to one inch long and shaped like little awls, growing in whorls of three. It is a dioecious, with male and female reproductive organs on different plants. Unlike our pines, which have woody cones, all of our junipers have seeds encased in cones that look like fleshy berries which are bluish black (common juniper) or blue-purple (our other three species). It takes common juniper seeds two three years to fully ripen before they can germinate. All four juniper species have male pollen cones are shaped like globose or ovoid catkins. The berries are a good food source for birds, especially thrushes, waxwings and grouse, and the seeds are resistant to digestion and pass through the bird for dispersal.

Common junipers grow in aspen and spruce-fir forests from 5,500 feet to 12,700 feet on the eastern and western slopes.

Utah juniper (Juniperus osteosperma) are trees or shrubs that grow to 2 to 4 meters tall on dry, rocky slopes, sometimes with pinyon pines or sagebrush on Colorado’s west slope from 4,300 to 7,700 feet. Unlike the common juniper, it has mostly opposite scale-like leaves that are 1 to 3 mm long and hug their stems; but like common junipers, it is dioecious and has berry-like seed cones which are green when immature and blue to bluish-purple when mature. The cones usually hold one to two seeds which take one to two years to mature after fertilization. The seeds are dispersed primarily by animals and birds, especially western bluebirds and American robins, but can also be dispersed by wind.

One-seed juniper (Juniperus monosperma) gets it species name from the fact that its berry-like cone contains only one seed. It grows as a shrub or a tree that is slightly taller than the Utah juniper, growing to 7 meters tall. Unlike Utah juniper, it is found primarily on the eastern slope of Colorado on dry, rocky slopes in the southern counties from 4,000 to 6,700 feet altitude.

It has both needle-like and scale-like leaves. The needle-like leaves are thin and pointed and appear on young plants or on the new shoots of mature plants. As the needles mature they shift to overlapping scale-like leaves which are somewhat appressed to the stem.

Like the other junipers, its seeds are primarily dispersed by birds, but are also dispersed by animals. Its fruit tastes slightly sweet and aromatic and can also be used to flavor foods, or used in the production of gin.

And finally, our fourth species of juniper is Rocky Mountain juniper (Juniperus scopulorum). It grows only as a tree from 3 to 6 meters tall in a variety of habitats, from sagebrush, to pinyon pine, ponderosa pine and oak communities from 4,000 to 10,000 feet on the eastern and western slopes.
Like one-seed juniper it has needle-like leaves when immature and scale-like leaves when mature. Its fruits are also berry-like containing several seeds which mature in the second year after fertilization and are dispersed primarily by birds but also by animals.

The Ephedra Family (Ephedraceae)

The third family in the Colorado gymnosperms is the Ephedra family (Ephedraceae). It is the smallest family both worldwide, with only three genera, and in Colorado, where there is only one genus, Ephedra, with three species. Ephedra species are desert plants which only occur in the far west counties of Colorado. They are all leafless shrubs /with jointed, green stems, forming whorls of stems at nodes along the stalk. Like the pines, ephedra plants are dioecious, with male and female reproductive organs on separate plants. Ephedra plants produce naked seeds, but rather than forming in cones, the seeds grow in a colored, cup-like structure called a perianth. The female cones have bracts which cover two maturing seeds.

Their common name “Mormon Tea comes from the fact that Mormons used the ephedra plant to brew tea. Native Americans also brewed the tea and used it to treat a wide variety of health issues including coughs and colds, kidney or bladder functions, stomach ailments, and the White Mountain Apache and Navahoe used it to treat gonorrhea and syphilis.

Green Ephedra (Ephedra viridis) and Nevada ephedra (Ephedra nevadensis) are characterized by having mostly opposite leaves and bracts. Green ephedra is the most common ephedra in Colorado, found in all ten of the Colorado counties on our western border with Utah. It grows on dry, rocky or sandy slopes and on mesa tops up to 7,500 feet. Nevada ephedra is rare in Colorado with only four collections in four counties on the western border. It has a slightly less altitudinal range from 5,000 to 6,500 feet.

The third species, Torrey’s ephedra (Ephedra torryana) is characterized by leaves and bracts which occur in whorls of three. It is slightly less common than green ephedra, occurring from 4,500 to 6,500 feet in altitude in the same habitats.

Photo Gallery of Gymnosperms

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