Mt. Pinos Onion (Allium howellii var. clokeyi) is a rare native perennial herb that grows in Southern and Central California, primarily in the Transverse Range region. It tends to grow in granitic soils, at elevations from 700-6100 feet.

Howell's Onion (Allium howellii var. howellii) is a common native perennial herb that grows in central California. It tends to grow in granitic soils, at elevations from 700-6100 feet.

Allium hyalinum is a species of wild onion known by the common name glassy onion. It is endemic to California, where it is a common species of the San Joaquin Valley and the Sierra Nevada foothills. The glassy onion grows from a cluster of bulbs, with each bulb sending up a tall stem. Atop each stem is an flower cluster of up to 25, but usually fewer, white or pink-tinted white flowers. The flowers have six shiny petals which become transparent as they age.

Allium jepsonii is a species of wild onion known by the common name Jepson's onion. It is endemic to the Sierra Nevada foothills of central California. This onion grows to a height between about 20 and 40 centimeters from one or two oval-shaped bulbs. There is a single cylindrical leaf which is about the same length as the stem. The flower cluster holds 20 to 60 small flowers, each under a centimeter long with pink-veined white petals with curling tips.

Allium lacunosum is a species of wild onion known by the common name pitted onion. It is endemic to California, where it is a common member of the flora in many types of habitat, from bayside to mountain to desert. This onion grows from a thick-coated yellowish-brown bulb one or two centimeters long. The stem reaches up to about 35 centimeters in maximum height and there are usually two leaves which may be as long or longer than the stem. The flower cluster contains up to 45 dark-veined white to pale pink flowers, each less than a centimeter long. There are four varieties of this species, three of which are somewhat uncommon.

Pitted Onion (Allium lacunosum var. lacunosum) is a common native perennial herb that grows in southern and central California. It tends to grow in drive open slopes, at elevations from 200-6900 feet.

Allium lemmonii is a species of wild onion known by the common name Lemmon's onion. It is native to the western United States, particularly higher-elevation areas in the Great Basin. Lemmon's onion grows from a bulb one and a half to two centimeters wide and has a short, flattened stem which is thin along the edges. Atop the stem is an flower cluster of 10 to 40 flowers which may be white to pink. The stamens may be light or dark in color. The ovary has a distinctive ridged mound shape in which all of the ovary parts appear melded together. This is a common plant in its native range. It favors dry clay soils.

Allium haematochiton is a North American species of wild onion known by the common name redskin onion. It is native to northern Baja California, Sonora, and southern California as far north as Kern County. It grows on the slopes of the hills and mountains, such as those of the Peninsular Ranges, Transverse Ranges, and southern California Coast Ranges. Allium haematochiton has a small rhizome associated with clusters of brightly colored red bulbs. From these grow several naked green stems, each with a few withering, curling leaves. Allium haematochiton has a small rhizome associated with clusters of brightly colored red bulbs. From these grow several naked green stems, each with a few withering, curling leaves. Atop each stem is an inflorescence of several flowers, each on a short pedicel. Each flower is just under a centimeter wide and white to pinkish with dark midveins. There are six stout stamens around a white or pink ovary. USDA Plants Profile

Allium membranaceum is an uncommon species of wild onion known by the common name papery onion. It is endemic to northern California, where it grows in wooded areas in the southernmost Cascade Range and Sierra Nevada foothills. This onion grows from a bulb just over a centimeter long which is sometimes associated with a cluster of smaller bulbs. The stem reaches a maximum height near 40 centimeters and there are two or three long, flat leaves about the same length. The flower cluster contains up to 35 flowers with white or pale pink petals which become papery as they age.

Allium monticola is an uncommon species of wild onion known by the common name San Bernardino Mountains onion. It is endemic to southern California, where it is found in the Transverse Ranges and the northernmost section of the Peninsular Ranges. It has been reported from San Bernardino, Los Angeles, Orange, Ventura and Santa Barbara Counties. Allium monticola generally grows in rocky areas at elevations 1400-3200 m. This onion grows from a bulb one or two centimeters long which often has daughter bulbs attached to it on stalks. The waxy stem reaches a maximum height near 25 centimeters and the single leaf may be a bit longer. The inflorescence contains up to about 25 flowers, each with tepals nearly two centimeters long and white or light pink with darker pink tips. Pollen and anthers are yellow.

Allium munzii is a rare species of wild onion known by the common name Munz's onion. It is endemic to western Riverside County, California, where it grows in the coastal sage scrub of the local hills and mountains at elevations of 400-900 m. It is known from only about fifteen occurrences and it is threatened by development of its habitat for human uses such as citrus agriculture and urbanization. It is a federally listed endangered species. Allium munzii is an onion that grows from a reddish brown bulb just over a centimeter long. It produces an erect stem up to about 35 centimeters in maximum height and a single leaf which is usually a bit longer. The umbel contains up to 35 flowers each under a centimeter long. They have tepals that are white with a dark green midvein, turning red with age. Pollen and anthers are yellow.

Allium nevadense is a species of wild onion known by the common name Nevada onion. It is native to the western United States where it grows in sand and rocky soil at elevations of 1400-1700 m. The species is widespread in Utah, Nevada and southern Idaho, and has been reported also from southeastern California (Inyo and San Bernardino Counties), northwestern Arizona (Mohave and Cochise Counties), western and central Colorado (Moffat, Garfield, Mesa and Boulder Counties) and eastern Oregon (Harney and Malheur Counties). The Nevada onion grows from a brown or gray bulb one to one and a half centimeters wide which may have one or two daughter bulblets associated with it. The stem may appear short if the bulb is more than a few inches below the surface of the ground. The stem is topped with an umbel of up to 25 flowers. The tepals may be white or pink-streaked with darker midveins; anthers purple; pollen yellow.

Allium obtusum is a species of wild onion known by the common name red Sierra onion. It is native to the granite hills and mountains of Nevada and eastern California where it is a common member of the local flora. The red Sierra onion grows from a bulb one or two centimeters wide and bears a stem which may be tall or short. Atop the stem is an flower cluster of up to 60 flowers which May 4 to 12 millimeters wide. The flowers are white to pink with dark midveins.

Red Sierra Onion (Allium obtusum var. conspicuum) is a common native perennial herb that grows in Central and Northern California, primarily in the Sierra Nevada Foothills and High Sierra Nevada regions. It tends to grow in granitic sands, at elevations from 2600-11500 feet.

Red Sierra Onion (Allium obtusum var. obtusum) is a common native perennial herb that grows in Central and Northern California, primarily in the High Cascade Range, the Sierra Nevada Foothills and High Sierra Nevada regions. It tends to grow in granitic sands, at elevations from 2600-11500 feet.

Allium parishii is an uncommon species of wild onion known by the common name Parish's onion. It is native to the Mojave Desert and Sonoran Deserts of California (San Bernardino, Riverside, and San Diego Counties) and Arizona (Yuma and Mohave Counties). It grows on open dry, rocky slopes at elevations of 900-1400 m. Allium parishii grows from a reddish brown bulb just over a centimeter long and produces a scape up to about 25 centimeters tall. There is a single cylindrical leaf which is generally longer than the stem. The umbel contains up to 25 dark-veined pale pink flowers with narrow tepals between one and two centimeters long. Anthers and pollen are yellow.

Allium parryi is a North American species of wild onion known by the common names Parry's onion and Parry's fringed onion. It is common in the Coast Ranges of southern California and northern Baja California. It is also known from the southernmost reaches of the Sierra Nevada. Allium parryi produceds a reddish brown bulb roughly a centimeter long. It produces a short stem up to a maximum height of about 20 centimeters and a single cylindrical leaf which is generally a bit longer. The inflorescence contains up to 50 pink-veined white flowers which turn darker pink as they age. Each flower has narrow tepals less than a centimeter long.

Allium parvum is a species of wild onion known by the common name small onion. It is native to the western United States where it is a common member of the flora in rocky, dry areas, especially in talus. This onion has a bulb one to two and a half centimeters wide and bears a relatively short stem for an onion species, reaching a maximum of 12 centimeters tall. The two leaves are sickle-shaped. Atop the stem is an flower cluster of fewer than 30 flowers, which are generally pale pink with prominent dark midveins. This plant was a food and flavoring for the Paiute people.

Allium peninsulare is a North American species of wild onion. It is known by such common names as Mexicali onion and Peninsula onion; the former referring to the Mexican city just south of the US/Mexican border, the latter referring to the Peninsula of Baja California. It is widespread in California, USA, where it grows in the California Coast Ranges, Sierra Nevada foothills, some of the Channel Islands, and Peninsular Ranges. The range extends south into the northernmost part of Baja California and north into southern Oregon. Allium peninsulare is usually found in Valley Grassland, Foothill Woodland, and Coastal Chaparral at elevations up to 1100 m (3660 feet). The plant produces a bulb 8-15 mm wide and has two to three channeled to more or less cylindrical leaves. Between May and July, it sends up a 12-45 cm scape topped with an umbel of 5-35 flowers, each on an 0. 8-4 cm pedicel. The flowers are red-purple and have six triangular tepals. The three inner tepals are smaller than the outer ones and have teeth along the margins. Allium peninsulare is usually found in Valley Grassland, Foothill Woodland, and Coastal Chaparral at elevations up to 1100 m (3660 feet). The plant produces a bulb 8-15 mm wide and has two to three channeled to more or less cylindrical leaves. Between May and July, it sends up a 12-45 cm scape topped with an umbel of 5-35 flowers, each on an 0. 8-4 cm pedicel. The flowers are red-purple and have six triangular tepals. The three inner tepals are smaller than the outer ones and have teeth along the margins. Varieties: Allium peninsulare var. franciscanum --- leaves arched; stigma, unlobed or obscurely 3- lobed --- central California from Mendocino County to Monterey County, Allium peninsulare var. peninsulare - leaves straight, stigma strongly 3 - lobed --- widespread from Baja California to Oregon

Allium platycaule is a species of wild onion known by the common name broadstemmed onion or flat-stem onion. It is native to northeastern California and nearby parts of Oregon and Nevada where it is found on slopes of some elevation. This onion grows from a gray bulb two to three centimeters wide and has a flattened stem which may bulge in the middle and narrow to thin wings along the sides. The long, flat leaves are sickle-shaped. Atop the stem is an flower cluster which may have as many as 90 flowers in it. Each flower may be up to a centimeter and a half wide but the petals are quite narrow so as to be almost threadlike. The flower cluster therefore may be a dense ball of filaments. The flowers are generally bright pink to magenta. The leaves, bulbs, and seeds were utilized as food by the Paiute people.

Allium praecox is a species of wild onion known by the common name early onion. It is native to the coastal hills and mountains of southern California and Baja California, including the Channel Islands, where it grows in shady areas in clay soils. This onion grows from a brownish or grayish bulb between one and two centimeters long. It produces a stem up to 60 centimeters long and two or three long, keeled leaves about the same length or sometimes a little longer. The flower cluster holds up to 40 flowers, each on a long pedicel up to 4 centimeters long. The flowers are purple-veined pink and dry to a papery texture as they age.

Allium sanbornii is a species of wild onion known by the common name Sanborn's onion. It is native to California and southern Oregon where it grows in the serpentine soils of the Cascade Range and Sierra Nevada foothills. This onion grows from a reddish brown bulb up to about 2.5 centimeters long. It produces a stem up to 60 centimeters long and a single cylindrical leaf which is about the same length. The flower cluster bears as many as 150 small flowers, each with petals less than a centimeter long in shades of pink to white.

Congdon's Onion (Allium sanbornii var. congdonii) is a rare native perennial herb that grows in Central and Northern California, primarily in the Sierra Nevada Foothills region. It tends to grow in rocky outcrops, at elevations from 1000-4600 feet.

Sanborn's Onion (Allium sanbornii var. sanbornii) is a rare native perennial herb that grows in Central and Northern California, primarily in the Cascade Range Foothills and Sierra Nevada Foothill region. It tends to grow in rocky outcrops, at elevations from 1000-4600 feet.

Allium serra is a species of wild onion known by several common names, including jeweled onion, pom-pon onion, and serrated onion. It is endemic to northern California. It favors hard soils with rock and clay, including serpentine soil. The plant comes from a small herringbone-patterned bulb an average of one centimeter in diameter. It has a long stem on which it bears a tightly bunched flower cluster of flowers. The attractive bright pink flowers are thimble or bell-shaped, often iridescent when new and becoming papery as they dry.

Allium sharsmithiae, called the Mount Hamilton onion or Helen Sharsmith's onion, is a rare species of wild onion endemic to a small region in California. It is found on serpentine soils in the vicinity of Mount Hamilton, in the Diablo Range south of San Francisco Bay in Santa Clara, Alameda and Stanislaus Counties. Allium sharsmithiae produces round to egg-shaped bulbs up to 2 cm in diameter. Flowering stalk is round in cross section, not hollow, up to 20 cm tall. Flowers are urn-shaped, up to 2 cm in diameter; tepals deep reddish-purple; anthers and pollen yellow.

Allium shevockii is a rare species of wild onion known by the common name Spanish Needle onion. It is found only in a limited area in the southern Sierra Nevada of California. The plant is endemic to southern California. Known locations occur in Spanish Needle Peak and Horse Canyon in the mountains of Kern County. The populations on Spanish Needle Peak are north of Owens Peak in the Sierra Nevada, near the boundaries with Tulare and Inyo Counties.

Allium siskiyouense is a species of wild onion known by the common name Siskiyou onion. It is native to the Klamath Mountains and nearby ranges of northern California and southern Oregon, where it grows in serpentine and other rocky soil types. This small onion plant grows from a reddish brown bulb one or two centimeters long. It produces a short stem no more than 8 centimeters long and two sickle-shaped leaves which are usually longer. The flower cluster contains up to about 35 flowers, each with dark-veined pink petals around a centimeter long and sometimes toothed at the tips.

Allium tolmiei is a species of wild onion native to the northwestern United States, and found in Lassen, Trinity and Modoc counties in California. It has white or pink flowers, and thick curving green leaves. Allium is the onion genus, with 600-750 species, making it one of the largest plant genera in the world. Tolmie's Onion is one of them. William Fraser Tolmie (aka "Dr. Tolmie") (February 3, 1812 - December 8, 1886) was a Canadian surgeon, fur trader, scientist, and politician. He was born in Inverness, Scotland in 1812 and by 1833 moved to the Pacific Northwest in the service of the Hudson's Bay Company (HBC). Plants bearing his name include Tolmie's star-tulip (Calochortus tolmiei) and Tolmie's onion (Allium tolmiei).

Tolm's Onion (Allium tolmiei var. tolmiei) is a uncommon native perennial herb that grows in Northern California, primarily in the Warner Mountains and Modoc Plateau regions. It tends to grow in rocky clay flats, at elevations from 4900-7200 feet.

Allium tribracteatum is a species of wild onion known by the common name threebract onion. It is endemic to California, where it is known only from the slopes of the Sierra Nevada in Tuolumne and Calaveras Counties. This is a small onion plant producing a stem only a few centimeters long from an oval-shaped bulb. There are two leaves which are usually much longer than the stem. The inflorescence contains up to 30 petite white to purple flowers, each less than a centimeter long.

Allium tuolumnense is a rare species of wild onion known by the common name Rawhide Hill onion. It is endemic to Tuolumne County, California, where it is known only from a small section of the Sierra Nevada foothills. It is a plant of serpentine soils. This onion grows from a reddish-brown bulb one to two centimeters long, producing a slender erect stem up to 50 centimeters tall and usually a single leaf approximately the same length. The stem is topped with a hemispheric flower cluster holding 20 to 60 flowers, each on a pedicel one or two centimeters long. Each flower is just under a centimeter wide when fully open, with six white or pink oval-shaped petals. There are six stamens and the ovary has six pointed crests.

Allium unifolium, the one-leaf onion or American garlic, is a North American species of wild onion. It is native to the coastal mountain ranges of California, Oregon, and Baja California. It grows on clay soils including serpentine, at elevations up to 1100 m. Allium unifolium, despite its name, usually has 2-3 flat leaves up to 50 cm long. Bulbs, though, are usually solitary, egg-shaped, up to 2 cm long, often formed at the end of rhizomes spreading out from the parent plant. Scapes are round in cross-section, up to 80 cm tall. Flowers are up to 15 mm across; tepals usually pink but occasionally white; anthers yellow or purple.

Allium validum, known by several common names including swamp onion, wild onion, and Pacific onion, has been previously classified as a member of the lily family, Liliaceae; however, it is now thought of to be in the Alliaceae. Allium validum is native to California. The Allium validum bulb is three to five centimeters long, ovoid and clustered on the short end. The outer coat of the stout rhizome is brown or gray in color, fibrous, and vertically lined. The stem is 50 to 100 centimeters long and angled. There are three to six leaves more or less equal to the stem and the leaves are flat or more or less keeled. There are 15 to 40 flowers with pedicels being seven to twelve millimeters in length. The flower itself is six to ten millimeters, its perianth parts are more or less erect, narrowly lance-shaped, acuminate, and entire with a rose to white color. The stamens are exerted and there is no ovary crest.

Allium yosemitense is a species of wild onion known by the common name Yosemite onion. It is endemic to the central Sierra Nevada of California, where it is known from only a few areas in the vicinity of Yosemite. This onion grows from a bulb two to three centimeters long, producing a stem up to about 23 centimeters in maximum height and two long, flat leaves which are usually a bit longer. The flower cluster bears up to 50 white or pink flowers, each on a pedicel which may be over 3 centimeters long.

Almutaster is a North American genus of plants in the aster fammily containing the single species Almutaster pauciflorus (formerly Aster pauciflorus), which is known by the common name alkali marsh aster. It is native to Canada (Northwest Territories and the 3 Prairie Provinces, the western United States, and northern and central Mexico (as far south as Tlaxcala). Almutaster pauciflorus grows in wet alkaline and saline soils such as inland salt marshes and salt flats. This is a perennial herb growing a reddish-green glandular stem to heights from 30 to 120 centimeters. The narrow leaves are linear in shape and up to 10 centimeters long. The inflorescence is an open array of flower heads containing white to pale purple ray florets and a center of yellow disc florets. The head is lined with phyllaries covered in tiny white resin glands. The fruit is a hairy achene.

Alnus incana (Grey or Speckled Alder) is a species in the Betulaceae (Birch) family with a wide range across the cooler parts of the Northern Hemisphere. In California it is found primarily in the Sierras. It is a small to medium size tree 15-20 meter tall with smooth grey bark even in old age, its life span being a maximum of 60-100 years. The leaves are matte green, ovoid, 5-11 centimeter long and 4-8 centimeter broad. The flowers are catkins, appearing early in spring before the leaves emerge, the male catkins pendulous and 5-10 centimeter long, the female catkins 1.5 centimeter long and one centimeter broad when mature in late autumn. The seeds are small, 1-2 millimeter long, and light brown with a narrow encircling wing. The Grey Alder has a shallow root system, and is marked not only by vigorous production of stump suckers, but also by root suckers, especially in the northern parts of its range. The wood resembles that of the black alder, but is somewhat paler and of little commercial value.

Mountain Alder (Alnus incana ssp. tenuifolia) is a native tree or shrub that grows in northern, southern and central California. It is fast growing and moderately long-lived. It grows in an upright form to a height of 20 feet, with active growth during the spring and summer. Flowers are purple and bloom in the early spring. Leaves are dark green and deciduous. It tends to grow in wet places, at elevations from 4500-8000 feet.

White alder (Alnus rhombifolia) is a fast-growing deciduous tree in the birch family (Betulaceae), native to western North America at elevations of 300–7,900 feet. It thrives in moist soils, often found along streambanks and other wet areas.

This tree provides excellent shade, with dark green leaves in summer that drop in winter. In early spring, before the leaves emerge, white alder produces noticeable male catkins, which hang in clusters and release large amounts of pollen. The female catkins mature in autumn, resembling small cones that may persist on the tree for up to a year.

White alder is heat and wind tolerant but requires deep watering to establish. Its roots can be invasive, so it should be planted with caution, especially near structures or small residential gardens. However, it is an excellent choice for woodland plantings and riparian areas.

This tree has high wildlife value. It serves as a larval food plant for the Western Tiger Swallowtail butterfly and provides habitat and food for various bird species.

Alnus rubra (red alder) is a deciduous broadleaf tree in the Betulaceae (Birch) family native to western North America. In California it is found primarily along the coast from San Luis Obispo County northward. In southern california Alnus rhombifolia is the more commonly found alder. Red Alder is the largest species of alder in North America and one of the largest in the world, reaching heights of 20-30 meters. The official tallest red alder (1979) stands 32 meters tall in Clatsop County, Oregon (USA). The name derives from the bright rusty red color that develops in bruised or scraped bark. The bark is mottled, ashy-gray and smooth, often draped with moss. Large trees are often unbranched for a considerable distance from the ground. The leaves are ovate, 7-15 centimeter long, with bluntly serrated edges and a distinct point at the end; the leaf margin is revolute, the very edge being curled under, a diagnostic character which distinguishes it from all other alders. The leaves turn yellow in the autumn before falling. The male flowers are dangling reddish catkins 10-15 centimeter long in early spring, and female flowers are erect catkins which develop into small, woody, superficially cone-like oval dry fruit 2-3 centimeter long. The flowers are wind pollinated, and a large amount of airborne pollen is produced in early spring. The seeds develop between the woody leaves of the 'cones' and are shed in the autumn and winter.

Surface roots can be problematic if the tree receives frequent, shallow watering. Better to water deep and infrequently. Established trees with deep roots can be surprisingly drought tolerant. This is a large tree that requires plenty of space. Best suited for restoration or large gardens with bioswales or streams.

Alnus viridis (Green Alder) is an alder with a wide range across the cooler parts of the Northern Hemisphere. It is a large shrub or small tree 3-12 meter tall with smooth grey bark even in old age. The leaves are shiny green, ovoid, 3-8 centimeter long and 2-6 centimeter broad. The flowers are catkins, appearing late in spring after the leaves emerge (unlike other alders which flower before leafing out); the male catkins are pendulous, 4-8 centimeter long, the female catkins 1 centimeter long and 0.7 centimeter broad when mature in late autumn, in clusters of 3-10 on a branched stem. The seeds are small, 1-2 millimeter long, light brown with a narrow encircling wing.

Sitka Alder (Alnus viridis ssp. sinuata) is a native tree or shrub that grows in Northern California, primarily in the North Coast, the Klamath Mountain Range and North Coast Range regions. It is slow growing and long-lived. It grows in an upright form to a height of 16 feet, with active growth during the spring and summer. Leaves are light-green and deciduous. It tends to grow in creek and meadow edges, at elevations from 3300-8900 feet.

Aloysia wrightii is a species of flowering plant in the verbena family known by the common names Wright's beebrush and oreganillo. It is native to the southwestern United States and northern Mexico, where it can be found in desert, scrub, and woodland habitat. This is a thickly branching shrub which reaches nearly two meters in maximum height and is generally rounded in form. It has small, oval-shaped to nearly round leaves each no more than two centimeters long. The leaves have lightly toothed edges and hairy undersides. The flower cluster is a narrow, woolly spike up to 6 centimeters long, with small, widely spaced white flowers.

Amaranthus blitoides, commonly called mat amaranth, prostrate pigweed, procumbent pigweed, prostrate amaranth, or matweed, is a glabrous annual plants species. It usually grows up to 0. 6 m, though it may grow up to 1 m (3 feet). It flowers in the summer to fall. It is believed to have been a native of the central or eastern United States, but it has naturalized in almost all of temperate North America. It has also naturalized in South America and Eurasia. Some authorities list it as an invasive species.

Amaranthus californicus is a species of flowering plant in the amaranth family known by the common name California amaranth. It is a glabrous monoecious annual that is native to most of the western United States and Canada. The plant grows from 10 to 50 centimeters tall. It is found in moist flats or near bodies of water, and blooms from summer to fall.

Amaranthus fimbriatus is a species of glabrous flowering plant. It is also known by common names such as fringed amaranth or fringed pigweed. The plant can often grow up to 0. 7 m (2 ft. ) in height. The flower is greenish to maroon. It is found in the Southwestern U. S. and in Mexico. It often grows on sandy, gravelly slopes or in disturbed habitats. It usually blooms after the summer rains in these arid regions. This is a California native plant that can become weedy in landscaping situations. 

Amaranthus palmeri is a species of edible flowering plant in the amaranth genus. It has several common names, including carelessweed, dioecious amaranth, Palmer's amaranth, Palmer amaranth, and Palmer's pigweed. It is native to most of the southern half of North America. Populations in the eastern United States are probably naturalized. It has also been introduced to Europe, Australia, and other areas. The plant is fast-growing and highly competitive.

Amaranthus powellii is a species of amaranth known by the common names Powell's amaranth and green amaranth. It is native to the southwestern United States and northern Mexico, but it is common throughout most of the rest of the temperate Americas as a naturalized species. It has also been introduced to other continents, including Australia and Europe. This is an erect annual herb growing to a maximum height near two meters. It has leaves up to 9 centimeters long, those on the upper part of the plant lance-shaped and lower on the stem diamond or roughly oval in shape. The inflorescence holds several long, narrow clusters of both male and female flowers interspersed with spiny green bracts. The fruit is a smooth dehiscent capsule about 3 millimeters long containing shiny reddish black seeds.

Amaranthus torreyi is a species of flowering plant that is sometimes considered to be a synonym of Amaranthus watsonii. Its common name is Torrey's Amaranth. It is native to the southwestern United States and northern Mexico.

Amaranthus watsonii is a species of amaranth known by the common name Watson's amaranth. It is native to the southwestern United States and northern Mexico, where it grows in sandy places such as deserts and beaches, and disturbed areas. It is also known as a rare introduced species in parts of Europe. This is an erect annual herb producing a glandular hairy stem to a maximum height of about a meter. The leaves are generally oval-shaped and up to 8 centimeters long, with a petiole of up to 9 centimeters. The species is dioecious, with male and female individuals producing different types of flowers. The inflorescence is a long spike cluster of flowers interspersed with spiny green glandular bracts. The fruit is a smooth capsule about 2 millimeters long that snaps in half to reveal a small shiny reddish black seed.

Ambrosia acanthicarpa is a species of ragweed known by the common names flatspine burr ragweed, annual burrweed, and annual bur-sage. This spiny, weedy plant grows in clumps of many erect stems which may reach over a meter in height. Its gray-green stems are covered in a coat of stiff, bristly hairs. The few rough leaves are several centimeters long. The racemes of flowers are more plentiful, with each hairy flower head a few millimeters wide. The spiny, burr-like pistillate heads have pointed, twisting leafs and the staminate heads are rounded. This ragweed is native to western North America. It is adaptable and grows well in disturbed areas, easily becoming weedy.

Ambrosia ambrosioides, also known as canyon ragweed or chicura is a ragweed found in the deserts of northern Mexico and ranging into the southern half of Arizona. Growing as a shrub from 1-2 meters high, its elongate, coarsely-toothed leaves range from 4-18 centimeter long and 1.5-4 centimeter wide. It is monoecious, with both terminal and axillary racemes consisting of staminate heads occurring above their pistillate counterparts. Flowering occurs mainly in February through April. The fruits are 10-15 millimeter burs covered with hooked spines.

Ambrosia chamissonis is a species of ragweed known by the common names Silver Burr Ragweed, Silver Beachweed and (Silver) Beach Bur(r). It is known from most of the coastline of western North America from Alaska to Baja California, where it is a resident of beaches and other sandy coastal habitat. This is a large, sprawling perennial herb exceeding three meters in maximum width. The stems are roughly or softly hairy and longitudinally ridged. The plentiful leaves are a few centimeters long, woolly and silver-green, and variable in shape. The plant is monoecious, with male and female flowers on each individual. Staminate (male) flower heads containing many pale colored florets occur at the tip of the flower cluster, with pistillate (female) flower heads clustered below them. Each pistillate head contains a single tiny flower which develops into a fruit. The fruit is a brown bur up to a centimeter wide covered in sharp spines.

Ambrosia chenopodiifolia is a species of ragweed known by the common name San Diego Burrsage or San Diego Burr Ragweed. It is native to Baja California, and California as far north as San Diego County, where it is a member of the coastal sage scrub plant community. This is a thickly branching shrub exceeding 3 meters in maximum height. The leaves are ovals up to 3 centimeters long and coated in white hairs. They are sometimes lobed. Like other ragweeds it is monoecious, with each flower cluster bearing heads of pistillate (female) flowers below a cluster of staminate (male) flowers. The flower cluster is spiny, especially when in fruit. The fruit is a spherical, woolly bur about half a centimeter long covered in hooked spines.

Ambrosia confertiflora is a North American species of ragweed known by the common name weakleaf bur ragweed. Ambrosia confertiflora is native to much of northern Mexico (from Sonora to Tamaulipas) and the southwestern United States from California east as far as Kansas, Oklahoma, and central Texas. It is also naturalized in various other regions and has been declared a noxious weed in Australia.