Flovvers bloom from April to July and fruits ripen from July to September. The 

 effect of elevation on the rate of flower and fruit development of most shrubs is well 

 illustrated by the following examples. Bitterbrush was in early fruit June 18, 1967, 

 at Pigeon Hollow in Sanpete County, Utah, 1,520 m (5,000 feet); it was in all stages of 

 flowering at Oaks Climatic Station in Ephraim Canyon, Utah, 2,380 m (7,800 feet); and 

 it was still in bud at Snowberry in Ephraim Canyon, 2,560 m (8,400 feet). 



Study of floral phenology indicated that the stigmas and stamens reach maturity 

 about the same time. A variety of bees and wasps frequent the blossoms, and ants, 

 aphids, and cicadas have also been found. Evidently, insects are important in the 

 pollination of the flowers in nature. Cicadas, however, may do considerable damage in 

 high population years. Wounds are made on twigs and branches by the ovipositor when 

 the eggs are deposited. Bitterbrush populations suffer occasional damage from tent 

 caterpillars. Antelope bitterbrush averages 15,400 cleaned seeds per pound (34/g) 

 (Plummer and others 1968). 



Eybvidization: Antelope bitterbrush crossed with cliffrose or desert bitterbrush 

 produces fertile hybrids in nature (fig. 22 and 26) . Hybridization between antelope 

 bitterbrush and cliffrose is very common throughout Utah where their ranges overlap. 

 Also, many F2 and backcross segregants are common. Careful examination reveals cliff- 

 rose traits in most populations of bitterbrush in the region. Evidently, s)Tnpatric 

 introgression is widespread between the two parent species. The hybrids have n - 

 9 chromosomes as do both parents (Stebbins 1959) . 



Viable seeds and seedlings which resemble the many natural hybrids have been ob- 

 tained by artificially pollinating emasculated flowers of bitterbrush with pollen from 

 cliffrose (fig. 36) and the cl if frose-bitterbrush hybrid (table 1). During the 1971 

 season, 19 plump, obviously filled seeds were obtained by using Apache plume {Fallugia 

 paradoxa) pollen on emasculated bitterbrush flowers (table 1). 



Viable seed has also been obtained when bitterbrush pollen was artificially applied 

 to emasculated flowers of Stansbury cliffrose, the cliffrose and bitterbrush hybrid, 

 and the pistillate flowers of Apache plume (table 1). 



Most antelope bitterbrush evidently is setf-incompatible. This conclusion was 

 dram since 17 bagged branches containing unemasculated bitterbrush flowers set only 

 four viable seeds over a 4 -year period. These four seeds were all produced on the same 

 branch in 1970. Mass pollination of bitterbrush flowers just as they begin to open is 

 probably sufficient for hybridization since results from the bagged, emasculated 

 controls suggest that emasculation is not necessary. Considerable time will be 

 saved by not having to emasculate each flower. Also, pistils will mature more seed 

 because they will not be damaged during emasculation procedures. 



Antelope bitterbrush is reported to have a chromosome number of n = 9 

 (Thomas 1957; Stebbins 1959). 



Distribution and Habitat: Antelope bitterbrush normally occurs in well -drained, 

 sandy, gravelly, or rocky soils throughout the sagebrush, juniper-pinyon, mountainbrush, 

 ponderosa pine, and lodgepole pine types at elevations from 60 m (200 feet) in the 

 Pacific Northwest to 3,510 m (11,500 feet) in the Sierra Nevada Mountains (Stanton 1959; 

 Nord 1965) . In Utah, bitterbrush does occur on some clay loams where deeper rock strata 

 furnish good drainage, and at least one form grows on a deep basic-clay loam where 

 drainage is poor. A prostrate form grows on deep acid-clay soils in Oregon. Bitter- 

 brush's range extends over much of temperate western America from California eastward 

 throughout the Rocky Mountains and from British Columbia southward to Arizona and New 

 Mexico (McMinn 1951; Stanton 1959; Hitchcock 1961). 



28 



