124 
PLANTS OF YELLOWSTONE NATIONAL PARK 
flowers. The bracts of the involucre are unequal and are arranged 
in several series. The pappus consists of numerous hairlike bristles. 
The following key will serve to distinguish the more common species: 
1. Rays white. 2. 
1. Rays blue, purple or violet. 5. 
2. Leaves linear or narrowly oblong. 3. 
2. Leaves broader, more or less lance-shaped. 4. 
3. Stem smooth or nearly so. Aster angustus. 
3. Stem hairy. Wreath aster (Aster multiflorus) . 
4. Stems stout. Leaves thin, 2 to 4 inches long. Heads rather large. Engel- 
mann aster ( Aster engelmannii). 
4. Stems slender. Leaves thickish, 1 to 2 inches long. Heads smaller. Aster 
elegans. 
5. Peduncles and involucre glandular. 6. 
5. Peduncles and involucre not glandular. 8. 
6. Leaves broadly linear. Aster campestris. 
6. Leaves ovate to oblong or lance-shaped. 7. 
7. Bracts of the involucre lance-shaped. Rays violet. Aster conspicuus. 
7. Bracts of the involucre linear. Rays violet-purple. Aster integrifolius. 
8. Outer bracts of the involucre as long as or longer than the inner. 9. 
8. Outer bracts of the involucre shorter than the inner. 10. 
9. Bracts erect. Aster aprieus. 
9. Bracts bent outward at the tip. Aster proximus. 
10. Hairs on the branches arranged in lines. 11. 
10. Hairs on the branches rather uniformly distributed. 12. 
11. All of the bracts narrowly linear. Aster caerulescens. 
11. Outer bracts broader than the inner. Aster laetevirens. 
12. Bracts oblanceolate, some of the outer ones blunt at the tip. Aster 
adscendens. 
12. Bracts oblong to lance-shaped or linear, all sharp-pointed. 13. 
13. Stem leaves oblanceolate to linear. 14. 
13. Stem leaves ovate to elliptic or lance-shaped. 15. 
14. Heads several to many in a panicle. Longleaf aster ( Aster longifolius) . 
14. Heads solitary or few in a flat-topped cluster. Aster fremontii. 
15. Stems unbranched or branched only at the top. Aster caribyi. 
15. Stems branched from the base. Aster meritus. 
In addition to the above Aster andinus , A. commutatus , A. fron- 
deus and A. meamsii have been reported as occurring in the park. 
MacJiaeranthera pulverulent a .—The characters of this plant are 
very similar to those of the true asters except that when the leaves 
are toothed they are usually bristle-tipped, and the bracts of the 
involucre usually curve outward more than in any of the true asters. 
The plant is small, 4 to 12 inches high, and more or less hairy. The 
lance-shaped leaves are rather small and scattered, some of them 
entire and some toothed. The heads are small and the rigid bracts 
of the involucre are in about three rows or more. There are only 
8 to 16 of the violet-purple ray flowers. 
