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• <br />On accoun[~ of its extensive underground system of rootstocks, western yarrow has <br />been reported to be a soil binder in certain types of erosion control on the <br />WasaCCh Plateau in central U[ah. When such plants are started near [he edges of <br />small gullies, their rootstocks soon spread down in all directions across the <br />depressions and serve to catch particles of sediment from water flowing past <br />them, Ch us forming small alluvial fans and checking surface run-off. <br />In addition to this vegetative propagation by rootstocks or rhizomes, western <br />yarrow also has fairly strong seed habits. I[ produces flowers practically <br />throughout [he summer, beginning as early as May or as late as September in the <br />higher mountains; subsequently [here is, in the case of the early-flowering <br />plants, a long period of seed production. The late-flowering plants, however, <br />often are unable [o set seed. <br />The leaves of western yarrow are mostly basal, often forming rosettes. These <br />lower leaves are stalked and are from 2 to 8 inches long, but the unpaired <br />• (alternate) stem leaves become increasingly shorter up the stem and are either <br />stalkless (sessile) or nearly so. The dense flower clusters at the ends of the <br />stems are somewhat flattened or convex like the [op of a derby hat. What appear <br />to be individual flowers are really flower heads, consisting of a group of flow- <br />ers (both ray and disk flowers) attached to a common base (receptacle), and <br />closely surrounded by a series Cinvolucre) of small bracts (phyllaries) that <br />overlap like shingles. <br />Lathyrus leucan[hus <br />(Aspen peavine) <br />Aspen peavine is a delicate, trailing, or climbing perennial herb with the grace- <br />ful, pealike, rather sweet-smelling blossoms so characteristic of many members of <br />the pea family (Leguminosae, or Fabaceae). This species is confined [o Che Rocky <br />Mountains, ranging from southern Idaho to Wyoming, New Mexico, and Arizona. It <br />is a plant of [he higher elevations and occurs in greatest abundance in the upper <br />aspen and spruce belts. Its preferred habitat is the rich, moist soils of aspen <br />. groves where it often makes up a large part of the undergrowth. This herb seldom <br />grows in stands dense enough [o exclude other species and is commonly associated <br />2-83 <br />