Flora of Northwestern U.S.

Carex aboriginum is a species of sedge endemic to Idaho in the western United States, known as Indian Valley sedge. It was not observed in the wild between 1910, when it was first described, and 1999. Until its rediscovery, C. aboriginum was considered the only plant native to Idaho to have become extinct, and it remains one of the state's rarest and most endangered plant species.

Allium aaseae, the Southern Idaho onion or Aase's onion, is a plant species endemic to southwestern Idaho. It has been reported from 6 counties: Elmore, Ada, Boise, Gem, Payette and Washington. The plant is named for American botanist Hannah Caroline Aase (1883-1980), at one time professor at Washington State University in Pullman. Allium aaseae grows on sandy and gravelly sites at elevations of 800–1100 m. It has egg-shaped bulbs up to 2 cm in diameter, and pink or white bell-shaped flowers up to 10 mm long.

Fritillaria gentneri, or Gentner's fritillary, is a rare species of flowering plant in the lily family Liliaceae, that is endemic to southwest Oregon and adjacent Siskiyou County, California, USA. Its habitat is dry, open woodlands and chaparral at 1,000–5,000 ft (300–1,520 m), where it blooms from March through July. However, most populations have generally finished blooming by the end of May. As with many plants, the lower elevations bloom earliest with the bloom period moving up following elevation.

Astragalus anisus is a species of flowering plant in the legume family known by the common name Gunnison milkvetch. It is endemic to Colorado in the United States, where it is limited to the Gunnison Basin of Gunnison and Saguache Counties. This plant is a small perennial herb growing from a woody taproot. The caudex is clothed with the remains of previous seasons' leaves. The leaves are up to 7 centimeters long and are compound, made up of up to 15 leaflets. The herbage is coated in silvery hairs. The pinkish purple flowers occur in May and June. They are up to 2 centimeters long. They are

Petrophytum cinerascens (orth. var. Petrophyton cinerascens) is a rare species of flowering plant in the rose family known by the common names halfshrub rockmat and Chelan rockmat. It is endemic to the state of Washington in the United States, where it occurs in just a few locations along the Columbia River in Chelan and Douglas Counties.

Kalmiopsis is a small genus of flowering plants in the family Ericaceae.

Astragalus aquilonius, the Lemhi milkvetch,is a milkvetch species belonging to the Fabaceae family. It is native to Idaho.

Allium scilloides, called the fragile onion, is a plant species endemic to the US State of Washington. It has been reported from only 4 counties, all on the eastern side of the Cascade Range: Klickitat, Kittitas, Yakima and Grant. It grows on barren, gravelly or rocky slopes at elevations of 300–1300 m. The species is sometimes cultivated in other regions as an ornamental.

Sclerocactus glaucus is a rare species of cactus known by the common name Colorado hookless cactus. It is endemic to Colorado in the United States, where it is known only from the area between Grand Junction and Montrose. It is a federally listed threatened species. The description of this species formerly included plants now belonging to Sclerocactus brevispinus and Sclerocactus wetlandicus, two cacti endemic to Utah. When the second of the two species was separated in 1994, the name S. glaucus was applied only to plants found in Colorado; it made the common name Uinta Basin hookless cactus

Kalmiopsis leachiana, commonly referred to as Siskiyou kalmiopsis, is a rare flowering plant endemic to the Siskiyou Mountains of southwest Oregon, where it is specially protected in the 179,755-acre (727.4 km2) Kalmiopsis Wilderness reserve. It was discovered in 1930 by Lilla Leach in the Gold Basin area. It is related to Kalmia in the family Ericaceae.

Aquilegia laramiensis is a species of flowering plant in the buttercup family known by the common name Laramie columbine. It is endemic to Wyoming in the United States, where it is known only from the Laramie Mountains. This rhizomatous perennial herb produces stems up to 25 centimeters (9.8 in) long. The leaves are compound, divided into leaflets. The nodding flowers have greenish white or lavender sepals up to 1.5 centimeters (0.59 in) in length. The cream-colored to lavender petals are up to 1.2 centimeters (0.47 in) long and have thick, hooked spurs. The fruit is a follicle up to 1.4

Viola flettii is a species of violet known by the common name Olympic violet. Native to the northeastern and eastern Olympic Mountains of Washington in northwestern United States, it occurs on rocky outcrops and talus at subalpine and alpine elevations, i.e., from 1,340–2,000 metres (4,400–6,560 ft), and blooms from June through August.

Erythronium elegans is a rare species of flowering plant in the lily family known by the common names Coast Range fawnlily and elegant fawnlily. It is endemic to Oregon in the United States, where it is known from about 12 occurrences in the northern Coast Range. This plant grows from a slender bulb 3 to 5 centimeters long. It produces two leaves up to 20 centimeters long which are green, sometimes with brownish or white mottling. The scape grows up to 30 centimeters tall and bears one to four flowers. The flower has six tepals, the inner three white and the outer three white tinged with

Campanula piperi (Olympic bellflower, Olympic harebell, Piper's bellflower) is a species of flowering plant in the bellflower family, Campanulaceae. It is native to the Olympic Mountains on the Olympic Peninsula in the U.S. state of Washington. It has also been noted on Vancouver Island, British Columbia.

Camassia howellii, commonly known as Howell's camas, is a species of perennial flowering plant in the family Asparagaceae endemic to western Oregon. Discovered in 1889, Camassia howellii is now considered to be imperiled due to residential development, mining and grazing.

Astragalus sinuatus is a species of flowering plant in the legume family known by the common name Whited's milkvetch. It is endemic to Washington in the United States, where it is limited to one creek drainage on the western edge of the Columbia Basin. Its range measures about ten square miles in Chelan and Kittitas Counties in the central part of the state. This perennial herb has stems up to about 45 centimeters long. In April and May it produces yellowish or cream-colored flowers with purple-tinged keels. The fruit is a legume pod which is so tough it sometimes requires pliers to crack it

Astragalus osterhoutii, or the Osterhout milkvetch or Kremmling milkvetch, is an endangered species of milkvetch, discovered and collected in 1905 at Sulfur Spring in Grand County Colorado by Colorado botanist George Everett Osterhout for which the plant was named. It is found in the U.S. state of Colorado, in a 13 kilometres (8.1 mi) radius near the town of Kremmling. The Osterhout milkvetch is a perennial dicot. It belongs to the pea family, Fabaceae, and is in the Astragalus L. genus. Conservation efforts are centered around maintaining the populations and habitat due to the limited

Astragalus microcymbus is a species of flowering plant in the legume family known by the common name skiff milkvetch. It is endemic to Colorado in the United States, where it is known from Gunnison County and the edge of Saguache County. It was discovered in 1945 by Rupert Barneby, a British botanist. Currently, skiff milkvetch is experiencing population declines and is listed as a Tier 1 species in the Rare Plant Addendum to the Colorado State Wildlife Action Plan.

Astragalus linifolius is a species of flowering plant in the legume family known by the common name Grand Junction milkvetch. It is endemic to Colorado in the United States, where it is only found on the Uncompahgre Plateau in Delta, Mesa, and Montrose Counties. There are 21 occurrences, mostly in the general vicinity of Grand Junction. This perennial herb grows up to 50 centimeters in height. In May and June it produces many white flowers with purple-tinged keels. The fruit is a red legume pod. It grows on adobe and sandstone in pinyon-juniper woodland and sagebrush habitat. This species is

Allium dictuon is a species of wild onion known by the common name Blue Mountain onion. It is native to a small section of the Blue Mountains straddling the border between southeastern Washington and northeastern Oregon in the United States. It grows in Columbia, Garfield and Walla Walla Counties in Washington, plus Umatilla and Wallowa Counties in Oregon.

Agrostis rossiae, or Ross' bentgrass, is a species of perennial or annual grass that is endemic to the Firehole River drainage and Shoshone Geyser Basin of Yellowstone National Park. It is one of 3 endemic plants to the park.

Trifolium thompsonii is a species of flowering plant in the legume family known by the common name Thompson's clover.

Erythronium quinaultense, the Quinault fawn-lily, is a rare plant species endemic to a small region around Lake Quinault in Olympic National Park, Washington state, United States. Erythronium quinaultense produces egg-shaped bulbs up to 75 millimetres (3.0 in) long. Leaves are up to 20 centimetres (7.9 in) long. Scape is up to 25 centimetres (9.8 in) long, bearing one to three flowers. Tepals have yellow, white and pink bands perpendicular to the veins.

Cardamine constancei is a rare, narrow-ranged species of perennial rhizomatous forb known by the common name Constance's bittercress. It is endemic to select tributaries of the Clearwater and Coeur d'Alene Rivers in Idaho.

Boechera gunnisoniana, or Gunnison's rockcress, is a perennial herb of the family Brassicaceae (the mustards). It grows on windswept ridges as well as on stoney hillsides in west-central Colorado. The plant has many slender, erect stems which may reach a height of 15 cm. Flowering time is from May to June. According to chromosome counts, this species is diploid (n=7 as in all Boechera species) which probably reproduces sexually.

Boechera fecunda (syn. Arabis fecunda) is a species of flowering plant in the mustard family known by the common names Mt. Sapphire rockcress and Sapphire rockcress. It is endemic to Montana in the United States, where there are twenty known occurrences in three counties.

Astragalus wetherillii is a species of flowering plant in the legume family known by the common name Wetherill's milkvetch. It is native to Colorado and Utah in the United States. This perennial herb grows from a taproot and a caudex which yields several stems. The stems are partly purplish or reddish in color and are finely hairy. The leaves are green, without the silvery hairs of some other Astragalus. Each leaf is up to 10 centimeters long and is made up of up to 15 leaflets. The flowers are white or lavender-tinted and roughly a centimeter long. The fruit is a legume pod with a single

Astragalus tyghensis is a species of flowering plant in the legume family known by the common name Tygh Valley milkvetch. It is endemic to Oregon in the United States, where it is known only from the Tygh Valley of Wasco County. This species is a perennial herb growing from a stout taproot and a branching caudex. The plant forms mats or clumps, with stems growing prostrate or upright and up to 55 centimeters long. Most of the plant is covered in long, silky hairs. The leaves are divided into a number of leaflets each up to 1.7 centimeters long. The inflorescence is a raceme of up to 40

Arabis aculeolata is a species of flowering plant in the mustard family known by the common name Waldo rockcress.

Aquilegia saximontana, the alpine dwarf columbine, dwarf blue columbine, or alpine columbine, is a perennial plant that comes from the buttercup family.