Question: Which genus is native to western North America, Purshia or Bulbinella?

Context paragraphs:
Adiantum aleuticum: Adiantum aleuticum, the western maidenhair fern or Aleutian maidenhair, is a species of fern in the genus "Adiantum", native mainly to western North America from the Aleutian Islands of Alaska, south to Chihuahua, and also locally in northeastern North America from Newfoundland south to Maryland.

Purshia tridentata: Purshia tridentata, with the common name bitterbrush, is a shrub in the genus "Purshia" of the family Rosaceae.  It is native to mountainous areas of western North America.

Pseudotsuga: Pseudotsuga is a genus of evergreen coniferous trees in the family Pinaceae.  Common names include Douglas fir, Douglas-fir, Douglas tree, and Oregon pine. " Pseudotsuga menziesii" is widespread in western North America and is an important source of timber.  The number of species has long been debated, but two in western North America and two to four in eastern Asia are commonly acknowledged.  Nineteenth-century botanists had problems in classifying Douglas-firs, due to the species' similarity to various other conifers better known at the time; they have at times been classified in "Pinus", "Picea", "Abies", "Tsuga", and even "Sequoia".  Because of their distinctive cones, Douglas-firs were finally placed in the new genus "Pseudotsuga" (meaning "false hemlock") by the French botanist Carrière in 1867.  The genus name has also been hyphenated as "Pseudo-tsuga".

Betula occidentalis: Betula occidentalis (Water Birch, also known as Red Birch) is a species of birch native to western North America, in Canada from Yukon east to western Ontario and southwards, and in the United States from eastern Washington east to western North Dakota, and south to eastern California, northern Arizona and northern New Mexico, and southwestern Alaska.  It typically occurs along streams in mountainous regions.

Edmontosaurus regalis: Edmontosaurus regalis is a species of comb-crested hadrosaurid (duck-billed) dinosaur.  Fossils of "E. regalis" have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago.  "E. regalis" was widely distributed across western North America, with fossil remains found from northern Alaska to Colorado.

Brachyhyops: "Brachyhyops" is an extinct genus of entelodont artiodactyl mammal that lived during the Eocene Epoch of western North America and southeastern Asia (including Mongolia, China, and Kazakhstan).  The first fossil remains of "Brachyhyops" are recorded from the late Eocene deposits of Beaver Divide in central Wyoming and discovered by paleontology crews from the Carnegie Museum of Natural History during the early 20th century.  The type species, "Brachyhyops wyomingensis", is based on a single skull and was named by E.H. Colbert in 1937, but was not officially described until 1938.  During the latter half of the 20th century, additional specimens from North America have been recorded from Saskatchewan and as far south as Texas, indicating that "Brachyhyops" had a broad distribution and was well-dispersed throughout western North America.

Purshia: Purshia (bitterbrush or cliff-rose) is a small genus of 5-8 species of flowering plants in the family Rosaceae, native to western North America, where they grow in dry climates from southeast British Columbia in Canada south throughout the western United States to northern Mexico.  The classification of "Purshia" within the Rosaceae has been unclear.  The genus was originally placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.

Sonoma orogeny: The Sonoma orogeny was a period of mountain building in western North America.  The exact age and structure of the Sonoma orogeny is controversial.  The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny.  The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent.  Evidence of this event has been reported throughout western North America, but most distinctly in northwest Nevada.

Rhododendron occidentale: Rhododendron occidentale, the western azalea or California azalea, is one of two deciduous "Rhododendron" species native to western North America (the other is "Rhododendron albiflorum").  The western azalea is known to occur as far north as Lincoln and Douglas Counties in Oregon and as far south as the mountains of San Diego county.  Typically found in the coastal ranges of western North America, it also grows in the Cascade and Sierra Nevada mountain ranges, but is not known east of them.

Bulbinella: Bulbinella is a genus of plant in the family Asphodelaceae, subfamily Asphodeloideae, first described as a genus in 1843.  Many species are endemic to Cape Province in western South Africa, confined to the winter rainfall area.  Other species are endemic to New Zealand, where they are most common in the central Otago region which enjoys a similar climate to the Cape Region of South Africa.

Supporting paragraphs: Purshia Bulbinella
Answer: Purshia