Shrubs Of The Great Basin: A Natural History

Bush Peppergrass

Bush Peppergrass Lepidium fremontii ALTHOUGH MANY MEMBERS of the mustard family are denizens of our deserts and mountains, the bush peppergrass is the only significant woody species here. In fact, only a few members of the genus to which it belongs are shrubs, and many are annuals which complete their life cycle within only a few weeks during spring in the desert. Actually, only the basal parts of the bush peppergrass are woody, and by some this plant would be considered to be a subshrub. Other names in common use are desert alyssum and Fre~ mont's peppergrass. L. fremontii is a low, rounded, many~branched shrub with whitish, waxy stems; it is frequent in sandy and rocky soils in the southern Great Basin, continuing on south into creosote bush and Joshua tree country. Generally, it is found between 2,000 and 5,000 feet. Although most manuals consider this a shrub of the southern deserts, in the western Great Basin it occurs as far north as the Granite Range in northern Washoe County. It is fairly com~ mon in shadscale desert areas in several western Nevada counties, especially in the vicinity of Pyramid Lake. The only other peppergrass with which this species might be confused is L. montanum, the mountain peppergrass. Both species may grow to a height of 20 or 30 centimeters, although the moun~ tain peppergrass tends to be smaller, has fewer stems, and is less woody than the bush peppergrass. In addition, L. montanum is distributed from sage~ brush areas out into the shadscale desert, and its range includes all of the northern Great Basin. With a hand lens, one can always separate these two species with ease, since the variety of the mountain peppergrass found predominantly within the Basin, canescens, has finely pubescent stems, while the bush peppergrass is always hairless. As the species name implies, L. montanum occurs at some~ what higher elevations, from 4,500 to 6,500 feet, although it is not really a mountain inhabitant. 119 Bush Peppergrass BUSH PEPPERGRASS 121 The genus name Lepidium comes from the Greek lepidion, which means little scale. This is in reference to the small, flattened, circular seed pods. The species name fremontii honors the explorer John Charles Fremont, who dubbed the area he had just traversed the "Great Basin" in 1844. The flowers in both species are white and borne on slender stalks along the axis of the inflorescence; the petals are only 2 or 3 millimeters long. Blooming occurs from spring to early summer. Following flowering, small, flattened, circular fruits develop. In the bush peppergrass the fruits have a wide, winged margin and are 5 to 6 millimeters long, while mountain peppergrass fruits have only a narrow margin and are only half as long. The stem leaves in the bush peppergrass are narrow and long, about 2 to 5 centimeters , with the lower ones sometimes possessing narrow lobes attached to the main axis. The mustard family, to which Lepidium belongs, is now called the Brassicaceae , although until recently it was known as the Cruciferae, in reference to the cross formed by the petals. All the mustards are characterized by a very regular arrangement and number of floral parts. They consistently have four sepals, four petals, six stamens, and one pistil. Because there is so little variation from this basic theme, this is one of the easiest families to recognize in the field. Not only the flowers but also the fruits of this family are distinctive, consisting of either elongated capsules, with the halves splitting away from each other to release the seeds, or short and frequently circular capsules like those of peppergrass, which contain fewer seeds but which nevertheless split open to release them in the same fashion. Structurally , the capsules are divided into halves by a membrane running down the center. Often, this central membrane remains attached to its stalk long after the seeds are shed. This is a distinctive feature, common to most mustards but infrequent in other families, at least in our area. Consequently, it is usually possible, even in the dead of winter, to recognize a mustard, though only a few lifeless stalks may be evident. The flowers of bush peppergrass are insect-pollinated, and it is known that some other mustards are important sources ofnectar and pollen for bees, though apparently the bush peppergrass has received no scientific attention on this point. Cattle appear to occasionally...