Shrubs Of The Great Basin: A Natural History

Parry's Rabbitbrush

Parry's Rabbitbrush Chrysothamnus parryi LIKE THE rubber rabbitbrush, which it much resembles, Parry's rabbitbrush has its branchlets covered with a whitish, feltlike pubescence. One major difference is that its flowers are borne in a spikelike affair at the branchlet endings, rather than in a relatively flat;topped or globose cluster, as in the rubber rabbitbrush. Another, frequently conspicuous difference is that the bracts surrounding the flowering head have very long and tapering tips, which tend to curl outward and down, a condition which botanists call squarrose. These same bracts in the rubber rabbitbrush are either blunt or are only moderately tapering, and they are not squarrose. Parry's rabbitbrush is relatively small, at most only 50 centimeters high. The leaves vary from I to 8 centimeters long and from .5 to 8 millimeters wide. As with the green and rubber rabbitbrushes, there are numerous sub; species; about twelve are presently recognized. A number ofthese are known only from very restricted locales in mountainous terrain. Although the range of habitats and distribution of Parry's rabbitbrush is much like that of the rubber and green rabbitbrushes, the shrub is not as abundant. This latter factor tends to result in smaller populations which are isolated from one an; other, particularly in mountainous areas. The end result is that chance plays much more of a role in the evolution of new forms, and evolution is, in a sense, speeded up. This is one reason why our mountain ranges and peaks have so many endemic species, species found there and nowhere else. Another dictum of this scheme ofevolution is that natural selection plays a much less important role in such locales than it does in large lowland popu; lations. This implies that many of the morphological differences by means of which we separate these mountain;inhabiting species are not necessarily 293 294 ASTERACEAE adaptive. As long as a slight change in form doesn't interfere with the basic physiology of a particular species, it will, in a sense, be tolerated. One subspecies, monocephalus, was originally found by P. B. Kennedy on the summit of Mount Rose, near Reno. However, it is not restricted to that locale; it is known to also occur in Mono and Tuolumne counties in Califor~ nia. This particular form has the flowering spikes reduced to one or two heads. The entire complex of this species ranges from California east to Nebraska and New Mexico. Although specific studies have not focused on Parry's rabbitbrush, its palatability and value to domesticated animals probably are about the same as those ofthe green and rubber rabbitbrushes. Unlike the rubber rabbitbrush which it resembles, however, it apparently does not have a significant rub~ ber content. The smaller forms of Parry's rabbitbrush also somewhat re~ semble species in a related genus known as Haplopappus or goldenbush. One species in particular, H. suffruticosus, the singlehead goldenbush, super~ ficially might be mistaken for Parry's rabbitbrush but differs in a number of ways. Generally smaller, from 10 to 30 centimeters high, it is not as woody and is more accurately classified as a subshrub, as are most of the other goldenbushes. The branchlets and leaves are covered with a fine glandular pubescence, which is very evident under the hand lens, and the leaves are proportional to their length (I to 3 centimeters), not as narrow as those of Parry's rabbitbrush; in addition, they have a somewhat crinkled appearance. The flowering heads have three to six strap~shaped or ray flowers, unlike those of any of the rabbitbrushes. Another species, the rubber weed, H. nanus, might also be mistaken for some kind of dwarf rabbitbrush, but, again, it has ray flowers and narrow leaves less than 2 centimeters long. It is a small shrub of cliffs and crevices in the arid portions of the Great Basin. About the only other goldenbush likely to be mistaken for a rabbitbrush is Bloomer's goldenbush, H. bloomeri, a.compact shrub from 15 to 50 cen~ timeters high with a thick, woody main stem. Its leaves resemble those of Parry's rabbitbrush, and the flower heads are in spikelike arrangements at the ends of the branchlets. Usually the heads have from one to five ray flowers, but sometimes these are lacking. The bracts surrounding the flower~ ing heads appear very different from those of the rabbitbrush; the innermost bracts have a prominent translucent margin, with long hairs all around the [3.141.24.134] Project MUSE (2024-04...