Variety AZT™: Cloned Quality and Uniformity
More than two decades ago, desert adapted landscape trees began gaining in popularity in southwestern landscape designs. Promoted primarily as an alternative to higher water demanding trees, landscape architects soon realized that desert trees could be used in both naturalistic re-creations of desert scenes and highly formal, more traditional landscape designs. Desert species grown from seed offered designers trees with widely varying forms and structures that would easily, and naturally mimic trees found in the surrounding Sonoran Desert. Formal or urban landscape designs called for trees with more uniform qualities and far less heterogeneous shapes and growth habits. Such trees could not be produced if propagated from collected seeds.
An alternative to seed production is vegetative propagation (also called clonal propagation or cloning). With cloning, plant parts (typically fresh, lush, green stem growth) are treated with plant growth hormones to encourage the formation of roots. Once rooted, cuttings are then grown like a typical seedling to ultimately produce saleable trees. In this way new plants, identical to the original "mother" plant, are produced. For the grower, rooting plant parts ensures greater uniformity and reduces the need and expense of repeated culling to remove seedlings with undesirable qualities. Cloning provides an effective and reliable method for producing large numbers of genetically uniform trees with similar form, structure, flower color, leaf pattern or any other desired quality or appearance. The challenges in bringing cloned trees to the market have been 1) selecting trees with desired physical characteristics (branch structure, flower color and amount, foliage) that also possessed sound horticultural qualities (well-distributed root mass, cold hardiness, growth rate and form) and 2) to produce these clones successfully and efficiently on a large scale for commercial nurseries. Careful selection and evaluation of foundation stock (“mother” plants) in conjunction with cloning techniques can improve tree performance and uniformity. Without careful screening, physically attractive trees can be introduced that are, in fact, genetically vulnerable to an assortment of unanticipated problems.
Arid Zone Trees (‘AZT™’) began its research on cloning desert trees with two objectives: 1) that there are many individual trees within a given desert tree species that may exhibit desirable characteristics for landscape applications; and 2) that all trees developed and marketed by ‘AZT™’ need to possess both desirable physical and horticultural characteristics. To satisfy both goals we embraced a multiple clone approach. By identifying several trees (‘Mother Trees”) from within a single species with varying desirable characteristics, we can offer uniformity while maintaining genetic diversity. This approach provides landscape architects with a choice between more rustic tree forms and more traditional forms when specifying desert adapted trees in their designs.
The search for new trees to clone is ongoing and offers AZT the opportunity to introduce new clones when suitable selections are identified. We use the ‘AZT™’ variety name on all our cloned trees to allow us to add new selections as they are identified while still assuring our clients that all selections are the product of AZT’s screening and production processes.
All ‘AZT™’ varieties epitomize Arid Zone Trees’ commitment to quality and innovation.
Acacia smallii ‘AZT™’, Sweet Acacia AZT™
Acacia smallii ‘AZT™’, Sweet Acacia AZT™ are popular and well-adapted shade trees for arid region landscapes. Fragrant flowers, upright stature and rapid growth rate makes it desirable for commercial and residential landscapes. It is used as a theme tree in streetscape planting or at development entries but is probably most often used as individual accent trees in mixed desert planting. At maturity trees may reach 35’ to 45’tall and 30’ wide.
Sweet Acacia, grown from collected seed, exhibited such high levels of undesirable physical and genetic variabilities that the trees fell out of favor with the landscape design community. Variations included canopy and leaf density, bark texture, branching and varying flowering seasons. The most critically issues were wide and significant differences in cold hardiness have led to catastrophic damage to cold tender trees during periodic severe desert freezes.
To develop Acacia smallii ‘AZT™’, Sweet Acacia AZT™ we identified Mother trees with upright growth, open branch angles, brilliant, abundant flowers, and cold hardiness to 20 F. As the newest addition to ‘Variety AZT’, Acacia smallii ‘AZT™’ brings uniformity, durability, and beauty to the desert landscape palette.
Parkinsonia (Cercidium) Hybrid ‘AZT™’, Thornless hybrid Palo Verde ‘AZT™’
Parkinsonia (Cercidium) Hybrid ‘AZT™’, Thornless hybrid Palo Verde ‘AZT™’ is a thornless Palo Verde hybrid that exhibits qualities found in Palo Brea, Blue and Mexican Palo Verde. The canopy is lush green and provides ample shade. This ‘Variety AZT’ selection exhibits distinctive rich, green trunks and branches that, like the Palo Brea, remain smooth as they mature, is thornless, has a semi-evergreen growth habit and brilliant yellow flowers that appear abundantly in spring and intermittently during the summer months.
Parkinsonia (Cercidium) praecox ‘AZT™’, Sonoran Palo Verde ‘AZT™’.
Parkinsonia (Cercidium) praecox ‘AZT™’, ‘AZT™’ Sonoran Palo Verde has dark blue-green leaves and trunks, produces brilliant yellow blooms that appear abundantly in spring and intermittently during the summer and fall months and is cold hardy to the upper teens to low 20’s F.
Chilopsis linearis Bi-Color ‘AZT™’, Bi-Color’ Desert Willow ‘AZT™.
Chilopsis linearis Bi-Color ‘AZT™’, Desert Willow The produces abundant blooms during the late spring and summer growing seasons displayed against a canopy of narrow, weepy, deep green leaves. This combination of qualities makes the tree a striking and colorful addition to the landscape. The floral characteristic that sets this ‘AZT™’ clone apart from seed selections are burgundy-colored petals contrasting with a pink throat.
Chilopsis linearis ‘Desert Amethyst AZT™’, Desert Willow AZT™’
Chilopsis linearis ‘Desert Amethyst ‘AZT™’, Desert Amethyst’ Desert Willow ‘AZT™ has solid-colored, dark lavender flowers combined with wider, more upright leaves.’ Desert Amethyst’ ‘AZT™, like Bi-Color ‘AZT™’, brings generous shade and much needed summer color to desert landscapes.
Chilopsis linearis ‘Dora’s Desert Rose AZT™’, ‘Dora’s Desert Rose AZT™’ Desert Willow
Dora's Desert Rose' takes its name from an inspirational gardener who always found a place to enhance her surrounding, no matter how modest, with a garden of roses. This selection provides pink flower petals accented with a blush of purple and yellow and very few seed pods. The leaves are wider and are held more upright. The 'AZT Dora's Desert Rose' produces abundant blooms during the growing season against a canopy of weepy, deep green leaves making the tree a colorful and striking addition to the landscape. Like ‘AZT Desert Amethyst’, and ‘AZT Bi-Color’, 'AZT Dora's Desert Rose', brings generous shade and much needed summer color to desert landscapes.
Olneya tesota ‘AZT™’, Desert Ironwood ‘AZT™’.
Olneya tesota ‘AZT™’, Desert Ironwood ‘AZT™’ brings faster, more uniform growth to this iconic tree of the Sonoran Desert while also exhibiting up-right, V-shaped trunks and branches, and larger leaflets. These qualities offer a new look for Ironwoods while retaining their graceful, chalk gray trunks and branches.
Prosopis juliflora (velutina) ‘AZT™’, Native Mesquite ‘AZT™’.
There is much disagreement within the botanical and horticultural literature as to what constitutes an authentic Native Mesquite. Some suggest that the tree is Prosopis velutina while others support claims that it is Prosopis juliflora. In contrast, the literature on the genus Prosopis generally agrees that nearly all the “species” within this genus freely hybridize and that many documented species are likely hybrids that can attribute their distinction to the area or region where they were studied and described. Scientific controversies aside Native Mesquite is among the most commonly found trees in the Sonoran Desert. We began developing Prosopis juliflora (velutina) ‘AZT™’, Native Mesquite ‘AZT™’ to bring greater uniformity in growth and form to this remarkable, uniquely Sonoran Desert tree. Additionally, this ‘AZT™’ variety is less attractive to vector insects (aphids, thrip, whiteflies or psyllids) reducing or eliminating the need for seasonal pesticide applications to control these pests.
Prosopis glandulosa thornless ‘AZT™’, Thornless Honey Mesquite ‘AZT™’.
Prosopis glandulosa thornless ‘AZT™’, Thornless Honey Mesquite ‘AZT™’ exhibits characteristics like traditional P. glandulosa with its willow-like appearance, delicate leaf canopy, and grayish sculptural trunk. The absence of thorns on the gently curving branches, the trees synchronous bud break and uniform growth between specimen are the features that set this ‘Variety AZT’ selection apart from seed selections. The absence of thorns makes Prosopis glandulosa thornless ‘AZT™’ ideal for landscape applications from re-vegetation of disturbed desert sites to streetscapes, park plantings and commercial and residential landscapes. The form and texture of Prosopis glandulosa Thornless ‘AZT™’ blend almost seamlessly with surrounding native Sonoran Desert trees and shrubs.
Prosopis Seedless Hybrid ‘AZT™’, Seedless Hybrid Mesquite ‘AZT™’.
Prosopis Seedless Hybrid ‘AZT™’, Seedless Hybrid Mesquite ‘AZT™’ exhibits a uniform appearance, upright growth, and strong branch angles. Leaflets give the canopy a lush dark green look. The characteristics that set this ‘AZT™’ clone variety apart from other seed or cloned selections is that it does not set seed pods (is seedless), has uniform upright growth, synchronous bud break and, with sound horticultural practices, root mass growth that is in proportion to canopy growth. The Prosopis Seedless Hybrid ‘AZT™” is ideal for landscape applications from re-vegetation of disturbed desert sites to streetscapes, park plantings and commercial and residential landscapes. Trees are semi-deciduous losing only a portion of the leaves in warmer winter locations. Leaves remaining through the winter are shed rapidly in spring just prior to bud break. In late spring this Mesquites produces a few yellow-green, unremarkable, catkin-like flowers that are sterile.
Prosopis thornless hybrid ‘AZT™’, Thornless Mesquite ‘AZT™’.
Prosopis thornless hybrid ‘AZT™’, Thornless Mesquite ‘AZT™’ exhibit a uniform appearance, upright growth, and strong branch angles. Leaflets give the canopy a lush green look. The characteristics that set these ‘AZT™’ clones apart from seed selections are the thornless, uniform upright growth and, with sound horticultural practices, root mass growth that is in proportion to canopy growth. Trees break bud synchronously and grow at a uniform rate, streamlining pruning, irrigation, and general maintenance.
Cercidium hybrid 'Desert Museum,' 'Desert Museum' Palo Verde
In the late 1970's Mark Dimmitt with the Arizona Sonora Desert Museum (ASDM) began noticing Blue Palo Verdes that exhibited characteristics suggesting they were hybrids of other Palo Verde species. Dimmitt eventually identified a thornless seedling as clearly superior to the others collected. Careful evaluation of the genetic composition of this hybrid, named 'Desert Museum', revealed it to be a complex hybrid having genetic characteristics from Mexican, Blue and Foothill Palo Verde. Trees have tolerated temperatures of 15 degrees without damage in Tucson. Flowers are slightly larger than those of Parkinsonia aculeata and other Parkinsonia (Cercidium) and trees have been observed to flower abundantly as early as mid-March in southern Arizona with intense, full bloom lasting into late spring and early summer. Intermittent flowering can continue into the mid to late fall. The V-shaped branching, thornless growth and ample shade make ‘Desert Museum’ a pedestrian friendly desert adapted tree that can and is used in a wide array of landscape applications.
Arid Zone Trees propagates 'Desert Museum' with the guidance and permission of the Arizona Sonora Desert Museum. Parkinsonia (Cercidium) Hybrid 'AZT™' is propagated and available exclusively from Arid Zone Trees.