Nature Profiles

Trees, Shrubs & Ferns of the Sonoran Desert

 

Desert Trees

Chilopsis linearis ssp. arcuata (Desert Willow)

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Saguaro NP East

This is the subspecies of Desert Willow present in Arizona.  It is a very distinctive small tree, immediately recognised even when not in flower, by its very long, very thin dull green leaves. 

Despite its common name, the plant is unrelated to the Willow family, and instead is a member of the tropical Bignoniaceae.  The nominate subspecies, which is only found from New Mexico eastwards, has straight rather than curved (arcuate) leaves.

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Olneya tesota (Ironwood)

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Saguaro NP West

One of the iconic trees of the Sonoran Desert, ironwood is locally common but has a rather restricted range.  It is found in lowland desert habitats in the south-western quarter of Arizona and the far south-east of California, south into northern Mexico. 

Its tiny grey-green rounded leaves on spiny branches make it easy to identify, and when flowering in late spring the tree is unmistakable when it becomes covered in pinkish-purple pea-flowers.

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Parkinsonia microphylla (Foothill Paloverde)

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Saguaro NP West

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Saguaro NP West

True desert survivors, Palo Verdes are able to thrive in the hottest and driest parts of the Sonoran Desert thanks to their photosynthetic stems, avoiding the need for leaves in the hottest part of the year, which are prone to water loss. 

Two similar native species are found in Arizona - P.microphylla and P.florida, along with an introduced Mexican species, P.aculeataP.florida has blue-green elongated leaves and branches, and P.aculeata has very long leaflets. 

P.microphylla has tiny, round yellow-green leaflets, as its Latin name would suggest.

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Saguaro NP East

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Saguaro NP West

 

 

Parkinsonia florida (Blue Palo Verde)

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Sabino Canyon, Santa Catalina Mountains

The second of the two native Sonoran Desert palo verdes, this species is instantly distinguished from its equally common cousin (see above) by its pale blue-grey branches and elongated leaves.

 

 

Fraxinus velutina (Velvet Ash)

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Saguaro NP East

This common tree of permanently damp sites is described in the Flora of Riparian Areas & Grasslands section of the site.

 

 

Tamarix chinensis (Five-stamen Tamarisk)

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Catalina SP

As its Latin name suggests, this tree is an alien species, orginating in Asia.  In the desert southwest it has become a serious invasive weed in riparian areas. 

Resembling a cedar, the individual leaves on the branches are scale-like and deciduous.  The tree is not a confier, however, and bears true flowers. 

Thanks to John Wiens for the identification.

 

 

Desert Shrubs

Acacia greggii (Catclaw Acacia)

acg
Saguaro NP West

Named for the short, hooked spines on the branches, this large shrub (or small tree) grows in a range of desert habitats in the southwest. 

The compound leaves are composed of grey-green obovate leaflets, resembling a mesquite.  The distinctive flowerheads are pale yellow and composed of many small flowers with long stamens, giving the flower clusters the appearance of a slender bottlebrush. 

Thanks to John Wiens for the identification.

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Acacia constricta (Whitethorn)

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Saguaro NP West

Aptly-named, Whitethorn is a medium-sized shrub of low-lying desert areas, found from central and southern Arizona through southern New Mexico, into Texas and south into Mexico.  The Latin name derives from the constrictions along the length of the seed pods.

 

 

Prosopis velutina (Velvet Mesquite)

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msq2Sabino Canyon, Santa Catalina Mountains

Common across the southern half of Arizona, Velvet Mesquite is an important plant for a variety of animals in the Sonoran Desert, providing shelter and food.   

The foliage and flowers of Velvet Mesquite are similar to Catclaw Acacia (see above), but the branches bear straight spines, rather than curved ones. 

Thanks to John Wiens for the identification.

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Fouquieria splendens (Ocotillo)

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Saguaro NP West

Truly one of the icons of the Sonoran Desert, this unmistakable spiny shrub is spectacular when in flower in the spring.

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Larrea tridentata (Creosotebush)

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Sabino Canyon, Santa Catalina Mountains

One of the dominant shrubs in the Sonoran Desert, this plant forms an important parts of the desert ecosystem, with its flowers producing nectar for bees, and its foliage providing shelter for animals and seedling cacti as well. 

Individual Creosotebush plants are very long-lived, spreading by underground suckers, which emerge to gradually form a ring around the original plant. 

Creosotebush is named for the strong odour of the foliage, which is especially evident in humid air after a rainstorm, or even when you cup your hands around a shoot and breathe on it.

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Saguaro NP East

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Sabino Canyon, Santa Catalina Mountains

 

 


 

Coursetia glandulosa (Rosary Babybonnets)

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Sabino Canyon, Santa Catalina Mountains

The bicoloured pea-flowers of this canyon-dwelling shrub make it easy to recognise.  It flowers early in the year, at the start of spring.

 

 

Hyptis emoryi (Desert Lavender)

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Saguaro NP West

This beautiful shrub is a desert-dwelling member of the Mint family (Labiatae).  It is found along desert washes and other warm sites where frosts are rare. 

Its common name derives from the lavender-scented foliage, rather than the colour of the flowers.

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Anisacanthus thurberi (Desert Honeysuckle)

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Saguaro NP East

The favoured habitat for this sprawling hummingbird-pollinated shrub is along desert washes and on rocky slopes at medium elevations in the desert.  Individual plants can grow to over 2 metres tall. 

The species is found in southern Arizona and New Mexico, as well as adjacent north-west Mexico. 

There are 3 other species of Anisacanthus in the United States.

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Simmondsia chinensis (Jojoba)

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Sabino Canyon, Santa Catalina Mountains

Well-known as a botanical ingredient in skin creams, Jojoba is found in foothills habitats in the Sonoran Desert, and in the United States is only found in central and southern Arizona. 

It can be recognised by its rounded, leathery leaves, which are followed by clustered male flowers and solitary females, which develop into edible nuts.

 

 

Celtis ehrenbergiana (Spiny / Desert Hackberry)

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both photos Saguaro NP West

Formerly known as C.pallida, this widespread spiny desert shrub is an important wildlife plant - its leaves are the foodplant for several butterfly species, and many birds and mammals eat the berries which appear in autumn. 

As a species, Desert Hackberry can be recognised by its grey zigzag branches which are armed with many sharp spines.  The alternate leaves have rather wavy margins which can be entire or slightly toothed. 

Desert Hackberry is limited to the southern half of the state, where it occurs over a wide altitudinal range.  Its distribution extends east as far as southern Texas, with an endangered outlying population in Florida.

 

 

Atriplex canescens (Four-wing Saltbush)

ac
Saguaro NP East

Widespread in a variety of alkaline habitats in the southwestern United States, Four-wing Saltbush is named for the distinctive four-winged fruits which appear on female plants. 

When these are not present, this shrub can be recognised by its scaly greyish stems and sessile, linear grey leaves, which are covered with scales.

 

 

Krameria grayi (White Ratany)

kg
Saguaro NP West

Widespread in the desert southwest, White Ratany can be recognised by its thin grey, hairy leaves and it attractive purple-red flowers. 

The very similar Range Ratany (K.parvifolia) has spiny fruits with barbs along the entire length of the spines, rather than just at the tip, as in K.grayi.

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Dalea pulchra (Santa Catalina Prairie Clover)

dp
Saguaro NP West

This pretty shrub is common in more rocky areas of the Sonoran Desert. 

The tiny leaves have a dense coating of velvety silver hairs to protect against water loss.

 

 

Encelia farinosa (Brittlebush)

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bbb

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Saguaro NP East

This small shrubby plant is one of the classic sights of spring in the Sonoran Desert.  In Saguaro National Park it can cover large areas yellow when in bloom.  It is a beautiful plant, with plentiful tall flower stems and hairy grey foliage. 

Very much a plant of warm deserts, it can be found in suitable habitat in California, Arizona, Nevada and Utah. 

There are 8 species of Encelia in the USA, including E.frutescens described below.  Like some other desert plants, this species exudes a chemical that inhibits the germination of seeds in the soil around it, thereby helping it survive in a habitat where resources are scarce.

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Encelia frutescens (Button Brittlebush)

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Sabino Canyon, Santa Catalina Mountains

Much more understaded than its showy relative described above, this plant is found in similar habitats, but is absent from Utah.

 

 

Parthenium incanum (Mariola)

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Saguaro NP East

Primarily a plant of higher elevations within the Chihuahuan Desert, Mariola has distinctive hairy grey leaves with undulate margins.  The smaller photo below shows the very small, understated white flowers.

Thanks to John Wiens for the identification.

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Baccharis sarothroides (Desert Broom)

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Ramsey Canyon, Santa Rita Mountains

Common throughout the desert southwest, this autumn and winter-flowering shrub can be seen at medium elevations, rather than in the lowlands. 

The narrow, broom-like foliage is characteristic, although this photo doesn't show it in much detail.  Plants are dioicous, with female plants (like the one shown here) bearing silky white, fluffy seedheads in spring. 

Thanks to John Wiens for the identification.

 

 

Hibiscus coulteri (Desert Rose Mallow)

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Sabino Canyon, Santa Catalina Mountains

There are three species of Hibiscus in Arizona, all related to the well-known tropical members of the genus. 

H.coulteri can be recognised by its pale yellow flowers with a red spot at the base of the petals, and by its linear leaves with red, toothed margins. 

It grows in rocky desert areas and canyon slopes, rather than along desert washes.

 

 

Calliandra eriophylla (Fairy Duster)

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Sabino Canyon, Santa Catalina Mountains

Fairy Duster is one of the most easily recognised Sonoran Desert plants.  It is common, and very conspicuous when in flower. 

It inhabits gravelly places in lowland desert areas throughout the south-west.

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Catalina SP

 

 

Fallugia paradoxa (Apache Plume)

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Catalina Highway, Santa Catalina Mountains

Well-known throughout the desert southwest, Apache Plume is an attractive shrub when in flower.  It is named for the fluffy red seed heads (one visible in this photo), named for their resemblance to Indian head-dresses.

 

 

Bahia absinthifolia (Hairyseed Bahia)

ba
Saguaro NP East

There are several similar-looking shrubby plants with yellow daisy flowers which flower in spring in southern Arizona.  This species can easily be distinguished from the others by its palmate silvery leaves.  The plant as a whole is also rather small. 

Commonest on calcaerous soils, it can be found throughout southern Arizona and eastwards as far as Texas.

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Guardiola platyphylla (Guardiola / Apache Plant)

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Molino Basin, Mount Lemmon, Santa Catalina Mountains

Although a poor photo, the distinctive feature of opposite, green leathery leaves which identifies Guardiola can be seen here.  The individual flowers are white and daisy-like. 

Guardiola is a monotypic genus in the United States, with G.platyphylla found only in Arizona, where it grows in rocky canyons. 

Thanks to John Wiens for the identification.

 

 

Zizyphus obtusifolia (Graythorn / Lotebush)

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Saguaro NP East

This spiny shrub is widespread throughout the south-western United States. 

It can be recognised by its pale greyish-greeen oblong leaves on very short stalks, and abundant long grey spines which are found along the length of the branches. 

Thanks to John Wiens for the identification.

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Kartchner Caverns SP

 

 

Lycium fremontii (Fremont Thornbush)

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Saguaro NP East

Several Lycium species are common in the Sonoran Desert, where they can be recognised by the short, grey-green, spatula-shaped leaves and bright orange-red fruits.  Lycium fremontii is best recognised by its purple flowers (other members of the genus are pink or green, and its pale foliage. 

L.palllidum (Rabbit Thorn) also has pale foliage with a bluish tinge, and its flowers are greenish-yellow and occurs at higher elevations.  L.fremontii is exclusively a low-elevation, desert species. 

Thanks to John Wiens for confirming the identification.

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Lycium berlandieri (Berlandier's Wolfberry)

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Saguaro NP West

lycb
Sabino Canyon, Santa Catalina Mountains

Although similar to other Lycium species, this shrub has spines on both the branch tip and along the branches themselves, flowers which are funnel-shaped, rather than tubular, and spherical, rather than ovoid fruits. 

Two varieties of this shrub are found in Arizona: var.longistylum and var.parviflorum

Thanks to John Wiens for the identifications (the second and third photos aren't certain!).

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Condalia warnockii var.kearneyi (Warnock Condalia)

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Saguaro NP East

One of four Condalia species found in Arizona, Warnock Condalia can be recognised by its spine-tipped branches, which are covered with crowded small leaves. 

Like other members of the genus, the fragrant flowers lack petals, and are followed by small red berries in autumn. 

Warnock Condalia is found at moderate elevations in Arizona, on dry, sloping habitats.  It is also found further east in New Mexico and Texas. 

Thanks to John Wiens for the identification.

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Crossosoma bigelovii (Ragged Rockflower)

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Molino Basin, Mount Lemmon, Santa Catalina Mountains

One of two North American Crossosoma species, this shrub can be found in dry, rocky canyons. 

The five-petalled flowers are fragrant (but, not knowing this, I didn't smell them at the time!), and appear in spring.  The species can be found in California and Nevada, as well as Arizona. 

Thanks to John Wiens for the identification.

 

 

Artemisia ludoviciana (Silver Wormwood)

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Saguaro NP East

Although growing in the desert in this photo, Silver Wormwood can be found in just about every state in the lower 48. 

A highly variable plant, eight subspecies are currently recognised in the US, with five occurring in Arizona. 

The silvery leaves can be entire or lobed, and are woolly underneath.  Spikes of tiny white flowers appear in the autumn. 

Thanks to John Wiens for the identification.

 

 

Dodonaea viscosa (Florida Hopbush)

ddn
Sabino Canyon, Santa Catalina Mountains

When fruiting, this shrub is easily recognised by the clustered, pale hop-like fruits at the end of the branches.  As well as resembling them visually, the fruits were also used as a substitute for true hops in making beer. 

Globally this highly variable shrub is very widespread - you can see photos of Australian plants (where the genus is most diverse) here and here

D.viscosa is the only native member of the genus in the United States and is found in Hawaii, California, southern Arizona and Florida.

 

 

Trixis californica (American Threefold)

tc
Sabino Canyon, Santa Catalina Mountains

One of many yellow-flowered spreading small shrubs of the desert southwest, T.californica can be recognised by its small many-rayed flower heads and smooth-edges green lance-shaped leaves. 

It can be found from California to Texas.

 

 

Bouvardia ternifolia (Firecrackerbush)

bvd
Molino Basin, Santa Catalina Mountains

This attractive upright small shrub inhabits dry desert canyons and is easily recognised by its tubular red flowers and dark green lanceolate leaves. 

In Arizona, this species is very much restricted to the southeastern corner of the state, from where it ranges east as far as Texas.

Like many tubular-flowered desert plants, Bouvardia is pollinated by hummingbirds, and forms an important nectar source in habitats where it grows.

 

 

Eriogonum fasciculatum (Flat-top Buckwheat)

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Molino Basin, Mount Lemmon, Santa Catalina Mountains

A widespread and variable species of the American south-west, Flat-top Buckwheat can be recognised by its flat-topped flower clusters (only in bud in this photo), and small, pale, oval leaves. 

Four varieities of this species are recognised in the United States, with two - var.polifolium and var.foliolosum - found in Arizona.  Two other varieties, including the nominate form, are restricted to California. 

Thanks to John Wiens for the identification.

 

 

Ferns

Pellaea truncata (Spiny Cliff Brake)

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Sabino Canyon, Santa Catalina Mountains

The small spear-shaped glaucous blue-grey pinnules contrasting with thin dark stipes help to identify this widespread fern of the south-west.  It is found in rocky habitats, often on cliff faces, as the common name suggests.

 

 

Astrolepis cochisensis ssp. cochisensis (Cochise Scaly Cloak Fern)

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Catalina SP

This common fern of rocky desert areas has simple pinnate fronds which are scaly on their upper surfaces.  Key features in distinguishing this species from other Astrolepis spp. are the entire pinnae lobes and entire rhizome scales. 

Two subspecies are present in Arizona: ssp.arizonica, which is endemic to Maricopa County and ssp.cochisensis, which is widespread.

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Frond underside

 

 

Notholaena standleyi (Star Cloak Fern)

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Saguaro NP West

A very easily-recognised ferns of the Chihuahuan Desert and adjacent areas, the pentagonal fronds are a common sight in rocky canyons in southern Arizona.

 

 

Cheilanthes lindheimeri (Fairyswords)

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Mount Lemmon, Santa Catalina Mountains

A frequent fern of rocky ledges in the Sonoran Desert, this fern can be recognised by its pale grey-green fronds, which grow upright from a creeping rhizome.

 

 

Cheilanthes wootonii (Wooton Lip Fern)

chlw
Box Canyon, Santa Rita Mountains

Similar to C.lindheimeri (see above), this fern inhabits similar rock ledge habitats, and can be recognised by its greener appearance, due to the glabrous nature of the frond upper sides.  A feature to look for through a hand lens is to examine the scales on the rachis, which are hairy only towards to base, rather than all the way up their margin.

Wooton Lip Fern has a scattered distribution throughout Arizona, roughly along a line trending northwest-southeast.

 

 

Cheilanthes yavapensis (Graceful Lip Fern) (probably)

chy
Kitt Peak, Quinlan Mountains

Similar to C.wootonii (above), Graceful Lip Fern can be recognised in its typical forms by the hairy upper surface of the pinnae.

The fern is found in northern and central parts of Arizona, and ranges east to the Trans-Pecos region of Texas.

Thanks to John Wiens for the identification.

 

 

Selaginella rupincola (Ledge Spikemoss)

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Sabino Canyon, Santa Catalina Mountains

One of eight Selaginella species found in Arizona, Ledge Spikemoss is restricted to the southeastern corner of Arizona, from where it ranges east to the Trans-Pecos in Texas.  It is a mat-forming plant, with erect stems and bristly leaves. 

Thanks to John Wiens for the identification.