By John Palka — Posted November 15, 2015
To enter a forest is to enter a world teeming with life, displaying, in Darwin’s words, forms most beautiful and most wonderful. Let us take a journey into the forest, look for some of these forms, and allow ourselves to wonder at their beauty and diversity.
The trees dominate the view and are the framework within which other forest organisms find their homes. In this first picture we see rhododendrons blooming against second-growth Douglas firs (whose scientific name is Pseudotsuga menzesii) in Rhododendron County Park on Whidbey Island outside of Seattle. During a few weeks in spring, the exact timing of which depends on the elevation, Washington’s forests glow with the flowers of the native rhody (Rhododendron macrophyllum, large-leaf rhododendron), which is why it has been designated as the Washington State flower.
In comparing these two plants we have our first encounter with diversity as a biologist sees it. Rhodies are obviously flowering plants, and biologists call the entire assemblage of flowering plants the angiosperms. Their seeds are enclosed in fruits, a characteristic that gives rise to their technical name. Douglas firs, on the other hand, bear cones rather than flowers. The seeds are formed between the scales of the cones but they are naked, not enclosed in any special structures. Biologists group all conifers, plus the familiar Gingko tree and a few other groups, together as the gymnosperms. This technical name refers to their naked seeds.
Gymnosperms are regarded as the more primitive group, and it is believed, partly on the basis of the fossil record, that angiosperms first diverged from them about 160 million years ago. Today, the two coexist happily. Evolutionary divergence does not imply incompatibility except in a reproductive sense – angiosperms and gymnosperms do not interbreed!
This picture, taken along the Wilbert Trail in South Whidbey State Park (located on Whidbey Island north of Seattle), shows a different clustering of plants. The view is dominated by the base of a bigleaf maple (Acer macrophyllum) completely covered by mosses, with a sword fern (Polystichum munitum) in front. In the background, between the two trunks of the maple, are the drooping boughs of a young western hemlock (Tsuga heterophylla). The hemlock is a conifer and therefore a gymnosperm, and the maple is a flowering plant and therefore an angiosperm. They differ in another way as well: the hemlock is evergreen, as are most gymnosperms, whereas the maple is deciduous, as are the majority of angiosperms.
Ferns belong to their own group, mosses belong to yet another. Both ferns and mosses bear green, leaf-like structures, but neither produces seeds at all. Ferns have a fossil history reaching back 360 million years, mosses at least 470 million years. When we encounter these beautiful plants, we are touching both the amazing diversity of life on Earth and the deep time through which this diversity has evolved.
There are other amazing groups of organisms in the forest, fungi, lichens, and slime molds among them. We will make their acquaintance in due course. For now, take a stroll through the forest, look around you, and marvel at the diversity. Find some mosses, ferns, gymnosperms, and angiosperms for yourself. Look carefully at the details of their leaves and stems. As you do this, keep in mind the hundreds of millions of years it took to produce the diversity we experience today.