Shrubs Of The Great Basin: A Natural History

Western Serviceberry

Western Serviceberry Amelanchier alnifolia OUR WESTERN SERVICEBERRY is consistent only in its extremely variable nature, perhaps more so than any other shrub we have. Its variability in~ eludes not only a number of differences in leaf and stem form but a large array of physiological types as well, which appear to be adapted to an assort~ ment of habitats. Western serviceberry can be found in habitats ranging from open, dry, and rocky slopes to the deep shade of coniferous forests. It is found from sea level in Washington State to well over 9,000 feet in the Sierra Nevada of California. In shaded locations it is a small, sprawling shrub, sometimes only a few centimeters high. In better~lighted locations, western serviceberry may get to be over 2 meters tall. Sometimes a few erect branches begin to grow near the center of what was a low shrub and, in this way, convert it within a few years into a small tree. Because of this variability, some botanists have characterized numerous forms of western serviceberry by a series of species and varietal names. One form, known as A. pumila, has leaves which at the most are only slightly pubescent at maturity; it is especially characteristic of damp woods. Another species, A. pallida, has leaves with a fine pubescence, particularly on the lower surface, and seven to nine pairs of lateral veins joining the midrib. This species is commonly found on dry, rocky slopes. Many of the specimens from the western Great Basin appear to belong to this form. Also common in dry habitats throughout the Great Basin is another species, A. utahensis. It is similar to the preceding species but has somewhat smaller flowers and leaves with nine to thirteen pairs of lateral veins. However, many botanists regard these names with some trepidation, because of the existence of many examples which are obviously intergrades. And the existence of numerous intergrading forms between two "species" is considered by some authorities 145 Western Serviceberry WESTERN SERVICEBERRY 147 to indicate that they are not really distinct species but only variations of one species. That is, species are supposed to maintain their integrity and not hybridize so readily (though many do). All taxonomists know, or think they know, the rules for defining a spe~ cies. I recall a three~day seminar at the Missouri Botanical Garden some years ago dealing with the topic, "What is a species?" There were nearly as many different opinions as there were speakers. One of the speakers, only half joking, suggested that a species was whatever you consider to be a spe~ cies. The problem basically involves getting other experts to agree with your characterization of any particular species. To a great extent, species recogni~ tion is as much an art as it is a science, at least in some genera. It is conceiv~ able, of course, that the western serviceberry is now experiencing a rapid evolution which in the course of a few thousand or tens of thousands ofyears will result in many new species. Because so little change is apparent in a human lifetime, we sometimes forget not only that evolution is a process that has operated over the last 3 billion years to create the myriad life forms which have become extinct as well as those which now exist on the earth, but that such evolution continues unabated today and will perpetually gen~ erate new species as long as life exists. It follows, then, that we will occa~ sionally see this process in operation to an extent that makes it difficult to categorize species in some genera. The leaves on the western serviceberry, simple and oval in shape, are about 2 to 4.5 centimeters long. They are prominently veined, and usually there are teeth along the leaf edge above its middle, although occasionally they extend to the base or are lacking altogether. The white flowers are usu~ ally produced several together on a central stalk. Like many other members of the rose family, to which the serviceberry belongs, there are five sepals and five petals. The sepals are fused at the base, along with the apex of the flower stalk, to the ovary of the pistil-the ovary is that part of the pistil which contains the ovules that later develop into seeds. Flowers built along these lines appear to have the sepals, petals, and stamens perched on top of the ovary and are...