Scientific: Erythrostemon mexicanus (Synonyms: Caesalpinia mexicana, Caesalpinia robinsoniana, Erythrostemon robinsonianus, Poincianella mexicana, Poincianella robinsoniana)
Common: There are many common names for this plant. They are Mexican bird-of-paradise, yellow bird-of-paradise, yellow bird, Mexican poincianella, Mexican caesalpinia, or Mexican poinciana. All of this is confusing and demonstrates why use of scientific names to properly identify landscape plant material is important.
Family: Fabaceae (Leguminosae)
Origin: northern Mexico into south Texas
Taxonomic musing: The Caesalpinia group [subfamily Caesalpinioideae (family Fabaceae or Leguminosae)] has been in a state of considerable taxonomic flux over the last 30 years. For practicing horticulturists intersted in calling plants by their 'right name', this has created much confusion - a real hot mess! Presently, I am using the botanical name for Mexican bird-of-paradise that was proposed by Gagnon, et al. (2016) in PhytoKeys 71:1-160 and accepted by WFO Plant List, even though ITIS continues to accept Poincianella mexicana (Taxonomic Serial No.: 184639) as the official scientific name. So you get my point? A real hot mess indeed.
Pronounciation: Er-y-thro-STEM-on mex-i-KAY-nus
Hardiness zones
Sunset 12-16, 18-23
USDA 9-11
Landscape Use: Large seasonal accent, a quick background shrub although the canopy is too sparse to make it screening plant, small multiple-trunk or standard tree, a good plant for transition areas in oasis landscape design themes.
Form & Character: Upright, sparse and open, arborescent character with age and training, festive, warm, and attracting, brittle.
Growth Habit: Evergreen, woody, broadleaf perennial large shrub. This fast-growing shrub is strongly upright and sprawling to 10 to 20 feet or more with a somewhat less than to equal spread. The 'Mexican bird' or 'yellow bird' has INCREDIBLY BRITTLE wood that one could actually smash up into a mulch material with bare hands.
Foliage/Texture: Leaves twice pinnately compound, leaflets to 3/4 inch or less, light green, stems without spines but with well-defined, light grayish white lenticels; medium fine texture.
Flowers & Fruits: Lemon yellow flowers on terminal racemes; fruits are green pods in terminal clusters, which ripen and turn brown in early summer, indehiscent. Pods are heavy and weigh down branches. When pods are dry and brown, the seeds will "crackle and pop" out of their pods if splashed with water.
Seasonal Color: Festive yellow color in early spring and late fall.
Temperature: Heat loving, more cold hardy than Caesalpinia pulcherrima, damaged by cold when temperatures fall below 25oF.
Light: Full sun
Soil: Tolerant, annual fertilization in late winter will increase growth and foliar canopy density, which is otherwise typically sparse to open.
Watering: Needs to be irrigated regularly during summer. Use irrigation throughout the year to regulate overall plant productivity.
Pruning: Because of its strong upright habit, training yellow or Mexican bird-of-paradise is difficult. I mostly choose to elevate the canopy base in order to train this shrub into a small multi-trunk landscape tree. In stark contrast, the 'Horticultural clods of Phoenix' (aka 'Hort clods') stubbornly do the only thing they know how to do, which is to repeatedly shear this shrub throughout the year into Oblivion. If one really desires a small working size, then I prescribe that it's better to extensively prune these shrubs to near ground level in late winter and then manage the regrowth by making selective heading and/or thinning cuts with hand-held pruners once a year in late May/early June so as to simultaneously reduce plant biovolume and remove the ugly clusters of brown fruit pods.
Propagation: Seed is by far the easiest way to propagate.
Disease and Pests: Sometimes white flies in late summer.
Additional comments: Mexican bird-of paradise is a perplexing landscape shrub that's well worth use in Phoenix landscapes if well situated. So what's the take home message?
My 'official' story line: Yellow or Mexican bird-of-paradise (or whatever common name you want to call it) is a servicable, LARGE accent shrub with an open canopy that can attain a 'small tree' stature with age and training. The wood is amazingly (shockingly) brittle with distinct lenticles. The beautiful lemon yellow spring flowers attract hummingbirds. The seed pods however are visually distracting and make this shrub look bad to almost goofy during late April and May.
The inside story: So here's my 'unofficial' storyline about yellow or Mexican bird-of-paradise.....This large shrub/small tree grows into the most awkward size for today's Disney cartoon desert landscapes. It's too small for the 'Horticultural clods of Phoenix', aka 'Hort clods' to say, "Hey man, this is a tree so let's limb it and lion's tail it like a mesquite". And it's too large for these same 'Hort clods' to say, "Hey man, this is a 'bush' so let's get out the gas-powered hedgers and 'trim' this guy up like we do to every other 'bush' in Phoenix". It's because of this awkward 'too small, yet too large' size that I recommend yellow or Mexican bird-of-paradise NEVER be planted where professional landscape gardeners (cough, cough, 'Hort clods') are employed to "mow, blow, and go".
One exception to the rule: One exception to the above storyline about yellow or Mexican bird-of-paradise is the patented hybrid cultivar called Caesalpinia x 'Sierra Sun PP#20584' (former genus name). It is simply beautiful. It is a rather open-canopied, asymmetrical, and free-flowering large shrub to small tree that'll grow to a height of 15 feet with near equal spread. It is so nice that 'Hort clods' should always be banned (by executive order) from coming close to this gem. 'Sierra Sun' just does not need to be pruned...cough, cough...sheared by them, like ever.
