Updated: Nov 16, 2021
X-Plants are not spin-offs from the X-Men. The "x" in front of or within the scientific name refers to pairing (crossing) at least two plants to create a new species. When the "x" is in front of the genus (the first name), it means at least two plants from different genera (plural for genus) were crossed. Think of celebrity couples names like "branjolina" or "bennifer" and you've got the right idea. If the "x" is located between the genus and the species epithet (the second name), then at least two plants from the same genus were crossed and created a new species epithet. In the case of this tree, Chilopsis linearis was crossed with Catalpa bignonioides to develop a tree with large, tubular flowers while being "desert tough," as Sunset describes. When designers are looking for a small-scale tree with showy flowers, x C. tashkentensis might be an option.
Although these hybrids were made in 1964 and first introduced to the United States in 1977, they were not given a name under the International Rules for Botanical Nomenclature until 1991. Recently, Walter Wisura, curator of living collections at Rancho Santa Ana Botanic Garden, and I named them x Chitalpa tashkentensis.
x Chitalpa tashkentensis has no common name. Since it would be unwise to call it, "That pretty tree with the pink flowers bearing a cross," or some such unhelpful descriptor, simply calling it Chitalpa will do. Some people might even accept chitalpa as its common name, like magnolia, which is also Magnolia, the Latin name for the genus. Am I getting off track? Okay, just notice when the scientific word is capitalized and in italics to note the difference from a common name (not in italics and only capitalized at the beginning of a title or sentence).
Finding the right place for this tree might be challenging. It can grow in a container for awhile, but eventually it will require root pruning if kept confined or should be planted in the ground. Located too close to a patio or walkway, the shear volume of flower drop might be a nuisance. Have an aphid infestation? Sticky aphid secretions and sooty mold may make the tree even less desirable. It is often used as a street tree, but the wood is considered "medium weak" according to Cal Poly's Urban Forest Ecosystems Institute. Streetscapes and patios once again might not be advisable, but individual circumstances may differ, such as low wind concerns, good pruning practices, and minimal traffic may present a desirable condition.
If those negative elements are concerning, consider this tree set within a larger garden/landscape setting, away from people but close enough the appreciate the early summer bloom period. Having landscaping rather than concrete underneath them will allow summer blooms and autumn leaves to fall without compromising patios and sidewalks. A cluster might help with wind protection, both for the trees' health and the comfort of nearby people. Still not convinced? Consider this drought/heat resistant tree as a substitute for more sensitive species, such as flowering cherries.
Botanical Name: x Chitalpa tashkentensis
Chitalpa: Combined name (think of the genus as a super/celebrity couple name like "branjolina") Chilopsis x Catalpa.
Tashkentensis: The tree was hybridized in Tashkent, Uzbekistan
Common Name: Chitalpa
Family Name: Bignoniaceae
Origin: Cross development
Positioning: Wind-sheltered, residential, patio offset
Garden Themes: Cottage/informal, subtropical
Uses: Street tree, specimen, mass, summer screen (multi-trunk), shade tree (standard)
Type: Deciduous tree (multi-trunk or standard)
Form: Round, vase
Size: 20' to 30' tall and wide
Outstanding Feature(s): Flower
Bark: Light gray and scaly
Arrangement: Alternate to whorled
Color: Dull medium green (no notable fall color)
Surface: Fuzzy underside
Flower: Summer. Trumpet shape in terminal racemes. Light pink to white.
cultural requirements, tolerances & problems
Sunset Zones: 3-24
USDA Zones: 6-9
Light: Full sun
WUCOLS SF Bay Area Hydro Zone: Low
Texture: Loam, sand
Moisture Retention: Tolerates periods of dryness limiting water availability
pH: Lightly acidic to highly alkaline
Tolerances: Drought, heat, deer
Disease: Verticillium, root rot, mildew
citations & attributions
Elias, T. (n.d.). Chitalpas. Pacific Horticulture. Retrieved on July 12, 2021, from https://www.pacifichorticulture.org/articles/chitalpas/.
Missouri Botanical Garden. "x Chitalpa tashkentsis." Accessed on July 12, 2021 from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=e826.
NC State Extension. "Hemerocallis fulva." North Carolina State University, Raleigh. Accessed on July 11, 2021 from https://plants.ces.ncsu.edu/plants/hemerocallis-fulva/.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Urban Forest Ecosystems Institute SelecTree. "x Chitalpa tashkentsis Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on July 12, 2021 from http://selectree.calpoly.edu/tree-detail/1488.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on July 12, 2021 from https://ucanr.edu/sites/WUCOLS/Download_WUCOLS_IV_List/.
All photos by TELCS.