What have THEY done with my beloved Acacias?
Those damned botanists!
When us regular people try to keep track of all the plants out there, and do our best to learn a few botanical names, the botanists change the friggin’ names. There is a reason for this that we have discussed before.
Now, look what a mess they’ve made of the poor Acacias, the subject of this post.
Alas, there are no more new world Acacia species. Australia got to keep that name. Our plants have been assigned to numerous genera (not just one). Here is an introduction to the formally known as Acacias in our region.
Just about all these species are host to the Mexican and Mimosa yellow, and the marine and Reakirt’s Blue butterflies. Seeds of these species are used by granivorous birds.
Formally Acacia angustissima
If you know this plant from the United States, you know it as a deciduous shrub that grows in the grasslands in of Central and Southwestern United States, where it only reaches 3’ tall. But this species actually continues to occur south into Mexico, the tropics, and all the way into South America where it can become an upright tree to about 15 feet tall. Our version of the species is Acacia angustissima var. hirta, which is a dwarf. Throughout its wide range, this species has six varieties.
This is an excellent wildlife plant. Numerous butterflies and other nectar feeding insects visit the flowers, and several butterflies and moths use it as a larval food plant including the mimosa and mexican yellows, numerous skipper species, and the ceraunus and Reakirt’s blues. The gorgeous squirreltail fescue moth, a species of royal moth, also uses it as a larval food.
Because of its value as a nectar plant, this species is great planted with summer-active, native grasses. Plant it where you won’t mind it being dormant in the winter, and remove any dead stems in the spring.
In the tropics, the inner bark is used in the making of pulque, fermented agave beer. It was said to start the fermentation, but it turns out that the addition of the bark of this species imparted a stimulant effect (not unlike coffee) to the pulque. This species has a long history of medicinal use, and is also used in rangelands to improve soils.
Santa Rita Acacia
Formally Acacia millefolia
This deciduous shrub grows on ledges, in desert grassland, and on open rocky slopes and foothills at about 4,000-5,000 feet in elevation in Arizona, New Mexico (rare) south into Sonora, Chihuahua, and Sinaloa. Growing to about 10 or 12 feet tall and about 15 feet wide, this is a large deciduous shrub. Often it is found much smaller (about 6 feet tall) in the low desert. This plant takes moderate water and can take temperatures down to about 10°F.
The flowers are nectar-rich, blooming throughout warm weather, especially but not limited to summer. They attract butterflies, bees, and other nectar feeders.
It’s interesting that this is related to the palo blanco (Mariosousa willardiana). If you look closely at its leaves, especially the midrib of the leaf, you can kinda see how those two “acacia” species are close, and separate from the others.
Formally Acacia willardiana
This gorgeous tree suddenly appears in Sonora, Mexico, in rocky hillsides that sort of pop out of the thornscrub, sometimes seemingly straight out of rock. It needs little root room to thrive, and with its upright habit grows to about maybe 20 feet tall, often shorter. The willowy, swaying foliage is graceful, and the trunk peels back to expose a shiny white trunk, much like the ghost gum eucalyptus. It can take full sun and moderate to low water, when established. It is great planted against a wall so you can admire its trunk.
This tree is not to be confused with another similar-looking tree also called palo blanco (Lysiloma candida) which is mostly native to Baja California but is found in the Cajon del Diablo of Sonora, just north of Guaymas. It is VERY similar, but slightly taller, and slightly more frost-tender.
Formally known as Acacia berlandieri
Guajillo might be mistaken for feather tree (Lysilma watsonii), but with a much more upright shape, and is much hardier—guajillo is hardy to 10°F whereas feather tree suffers damage in the high 20s°F. Guajillo is very drought tolerant and where it is native, is valuable for being able to bloom in the most arid places, providing nectar to honey bees when little else is available. These trees don’t mind regular landscape watering and will grow fast, so long as they have good drainage. They are native to the southern part of Edwards Plateau in Texas south through northeastern Mexico to Hidalgo on rocky hills, slopes, sometimes in shell middens.
Formally known as Acacia greggii
Those who need to trek through areas dense with catclaw acacia, and perhaps one who have the task of doing some maintenance on one, may not have the nicest things to say about this plant. The thorns are formidable—curved and sharp. But the inconvenience such a plant may cause may be compensated by the amount of nectar this plant produces. The fuzzy, caterpillar-shaped flowers are cream-colored, and usually covered in bees of all sorts, as well as butterflies. Even the most shy butterflies, like the great purple hairstreak, may be seen at these flowers, since the amount of nectar provided by these flowers make exposing oneself worth the trouble. This plant usually grows upright to about 10 feet tall, or taller. In favorable conditions, it can become a 15-20’ tree, especially in well-drained but well-watered spots. This species is native to the southwest US (California, Nevada, Arizona, New Mexico, Utah, Texas, south into Northern Mexico including Baja California in flats, washes, and slopes below 5,000 feet in elevation. Grow in full to part sun, and use moderate water. This deciduous plant is hardy to 0°F.
This plant is used medicinally. Senegalia
Formally known as Acacia occidentalis
You might mistake this plant for a catclaw acacia, since it has the same catclaw-like thorns. But teso has very different flowers, seed pods, and attractive striations on the bark that set it apart from the other catclaw acacias. Otherwise in size and shape, its very similar. This plant is rarely available in the trade, but pops up occasionally. This species is found throughout Sonora, from the southern end, to the northern end almost into Arizona, and even east almost to Chihuahua, like it almost observes political boundaries!
Formally Acacia roemeriana
Another of the catclaw acacias, Roemer’s acacia grows about the same height. It has a rounded flower, instead of the caterpillar-shaped one that our Tucson basin catclaw has. The new growth almost has a reddish tint. Same benefits and uses as the aforementioned. Hardy to 15°F. Native to Texas, New Mexico, south into Chihuahua, Coahuila, and Nuevo Leon.
Formally known as Acacia wrightii
Wright’s acacia is slightly more tidy than the other catclaw acacias (usually growing to about 8 feet tall), and the bloom flush is aromatic and gorgeous. Native to arroyos, canyons, and hillsides in Central Texas west to New Mexico and south to Nuevo Leon in Mexico. Hardy to 0°F.
White Thorn Acacia
Formally Acacia constricta
White thorn acacia is native to the Tucson basin and a wonderful wildlife plant. These deciduous shrubs (rarely small trees) grow up to about 12 or even 15 feet tall but often found much shorter than that, usually about 5-6 feet tall. Plant in full sun, low to moderate water once established, with good drainage. Plants are hardy to -10°F.
They grow in dry slopes, washes, flat desert areas and mesas, often in shallow caliche soil in the southern half of Arizona, extending into New Mexico and West Texas. It grows in Mexico as far south as Oaxaca, with small populations in Baja California with some disjunct, naturalized populations in Maryland and Virginia. They grow in low to mid elevations.
Extrafloral nectaries grow along the main stem of the leaves, and attract ants to the trees. Flowers are, like all acacias, nectar rich and great for both native and domestic bees, butterflies, and other nectar-loving insects. Seeds are eaten by granivorous birds. They produce flowers even in the driest of years. A few species below are closely related (V. schottii, V. vernicosa, and V. rigidula. See their profiles for differences.
In the Sonoran Desert, Vachellia constricta grows in arroyos and washes, where it blooms in late spring (April–May), with a second round of blooms in July–October. Blooming requires a minimum amount of rain, followed by a period of warmth.
Formally Acacia farnesiana, often referred to in the trade as Acacia smallii
This is a relatively fast growing tree, especially in the first few years, and grows up to 35 feet tall, though often found much smaller, 15-20 feet. Trees are very upright, and bloom in spring, and sometimes fall, with very aromatic, yellow flowers that some people think they are allergic to (no Acacias are allergenic plants, because they have sticky pollen and are insect-pollinated). They happen to bloom right when some ragweeds and grasses are blooming, but they get blamed because they are conspicuous. Provide full sun, moderate to low water, and good drainage. Most plants in the trade are hardy from 15-20°F, but trees obtained from California or other sources can be very frost tender. The species varies a lot due to its wide distribution, and the more tropical versions of this tree will freeze at around 25-28°F. These may not be long-lived trees, especially if the soil doesn’t have good drainage.
The sweet acacia now grows all over the world. While the point of origin is thought to be the Caribbean, the Guianas, Mexico and/or Central America, the species has a pantropical distribution incorporating most of the Americas (from southern USA to Chile, excluding the Amazon). It has been naturalized, and in some places is an invasive species in tropical and subtropical areas of Australia, Europe, the Middle East, Africa, and Southern Asia. In the United States it is thought to be native to southern Texas, southern New Mexico, southern Arizona and southern California (though this is disputed too). It has naturalized in Louisiana, Mississippi, Alabama, Georgia and Florida mostly in coastal areas.
Flowers are the source of a commercial perfume used extensively in the cosmetic trade called cassie or huisache. Same wildlife benefits as V. constricta.
Formally known as Acacia rididula
Though closely related to the whitethorn acacia, this species is distinct with its darker green leaves contrasted by light-gray, almost whitish stems. It grows from 12-15 feet tall though found much smaller usually. It is almost like a shrubby version of Texas ebony. In Tucson it is evergreen, and in colder regions it may be semi-evergreen. Hardy to 15°F.
Blackbrush Acacia grows on limestone hillsides and canyons. Its native range stretches from Texas in the United States south to central Mexico.
Blackbrush extracts are used in weight loss dietary supplements. Same wildlife benefits as whitethorn acacia.
Formally known as Acacia schaffneri
If you want a sweet-smelling acacia, and you can find this species, we recommend it over the regular sweet acacia. Twisted acacia sports a canopy that recalls Medusa, from Greek myth, with the head of snakes for hair that would turn any onlooker into stone with one look upon her ugly face. Twisted acacia is not ugly though—it’s gorgeous, with dark green leaves that are tightly whorled around the stems, which arch into the sky like Medusa’s snakes. The leaves are mostly evergreen in Tucson, semi-evergreen in cooler parts of our region. Hardy to 15°F.
Twisted acacia is native to the very southern tip of Texas, south throughout most of Mexico. It has all the same wildlife benefits as whitethorn acacia.
Formally known as Acacia schottii
The shorter stature and fine foliage of Schott’s acacia distinguishes it from whitethorn and other similar, related species. This one only grows about 4 feet tall but spreads a bit wider (about 5 feet). Deciduous, it is hardy to about 10°F. Grow in full sun, and water moderately with good drainage. Very rare in the trade.
Like many related species, it grows on limestones soils and can be found in Texas and neighboring Chihuahua. Same wildlife benefits as whitethorn acacia.
Formally known as Acacia neovernicosa or A. vernicosa
Viscid acacia is distinguished form whitethorn acacia by having 1-2 (occasionally 3) pairs of leaflets (3-7 in whitethorn acacia), resinous foliage and a consistently shorter stature, up to about 10 feet though most often found much shorter, at about 5-6 feet tall. The stems (which are not as dense in viscid acacia) arch upward giving the shrubs an almost wispy look. Grow in full sun, moderate to low water once established, good drainage, plants are hardy to 0°F.
This is very much a Chihuahuan Desert species, though at its margins, it shows up in the Sonoran Desert and desert grasslands. It grows on limestone, on rocky slopes and plains in Western Texas, southern New Mexico, and Arizona; Chihuahua and Sonora south to Zacatecas and Puebla, Mexico.