The honey locust (Gleditsia triacanthos), also known as the thorny locust or thorny honeylocust, is a deciduous tree in the family Fabaceae, native to central North America where it is mostly found in the moist soil of river valleys. Honey locust trees are highly adaptable to different environments, and the species has been introduced worldwide. Outside its natural range it can be an aggressive, damaging invasive species. They exhibit fast growth, but live a medium life span, as long as 125 years. The leaves are pinnately compound on older trees but bipinnately compound on vigorous young trees. The leaves are green in summer and turn yellow in autumn in shades ranging from cream and tan to golden yellow. Honey locusts leaf out relatively late in spring, but generally slightly earlier than the black locust (Robinia pseudoacacia).
The strongly scented flowers appear in late spring. Each cluster is a raceme 3–7 centimeters long with many tiny greenish-yellow to greenish-white flowers. The trees are polygamous-dioecious: many trees have only pollen producing flowers or seed producing flowers (strictly dioecious), but some will have both types of flowers in separate clusters, though usually one type will predominate.
The fruit of the honey locust is a flat pod (a legume) that matures in early autumn and is often twisted or curved. Pods may be produced from mid-September through mid-October in its native habitat.
Honey locusts commonly have thorns long growing out of the branches and trunk, some reaching lengths of ; and the USDA Natural Resources Conservation Service PLANTS database is the subordinate taxon Gleditsia triacanthos var. inermis. However, this scientific name is still found in gardening websites and books to distinguish thornless trees.
{|class="wikitable sortable mw-collapsible mw-collapsed" id="Synonyms"
|+ class="nowrap" | Table of Synonyms
! Name
! Year
! Rank
! Notes
|-
| Acacia villaregalis
| 1987
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Caesalpiniodes heterophyllum
| 1891
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Caesalpiniodes triacanthum
| 1891
|data-sort-value=A | species
|data-sort-value=A | ≡ hom.
|-
| Gleditsia brachycarpos
| 1813
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia bujotii
| 1845
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia bujotii var. pendula
| 1900
|data-sort-value=D | variety
|data-sort-value=B | = het., pro syn.
|-
| Gleditsia bujotii pendula
| 1857
|data-sort-value=J |
|data-sort-value=B | = het., nom. nud.
|-
| Gleditsia elegans
| 1796
|data-sort-value=A | species
|data-sort-value=A | ≡ hom., nom. superfl.
|-
| Gleditsia excelsa-pendula
| 1887
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia ferox
| 1809
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia ferox var. nana
| 1900
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia flava
| 1869
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia heterophylla
| 1817
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia horrida
| 1796
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia inermis var. elegantissima
| 1905
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia laevis
| 1830
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia latisiliqua
| 1830
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia meliloba
| 1788
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia micracantha
| 1887
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia mimosifolia
| 1859
|data-sort-value=A | species
|data-sort-value=B | = het., nom. subnud.
|-
| Gleditsia mimosifolia var. pendula
| 1859
|data-sort-value=D | variety
|data-sort-value=B | = het., not validly publ.
|-
| Gleditsia polysperma
| 1812
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia sinensis var. nana
| 1838
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia spinosa
| 1785
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. brachycarpos
| 1803
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos f. brachycarpos
| 1907
|data-sort-value=F | form
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. bujotii
| 1900
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos f. elegantissima
| 1949
|data-sort-value=F | form
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. ferox
| 1907
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. horrida
| 1789
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. inermis
| 1790
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos f. inermis
| 1903
|data-sort-value=F | form
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. laevis
| 1853
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. macrocarpos
| 1803
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. nana
| 1912
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos f. nana
| 1949
|data-sort-value=F | form
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos f. pendula
| 1949
|data-sort-value=F | form
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos lusus pendula
| 1907
|data-sort-value=G | sport
|data-sort-value=B | = het.
|-
| Gleditsia triacanthos var. polysperma
| 1789
|data-sort-value=D | variety
|data-sort-value=B | = het.
|-
| Melilobus heterophyla
| 1838
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
| Vachellia villaregalis
| 2005
|data-sort-value=A | species
|data-sort-value=B | = het.
|-
!colspan=4 style="text-align: left;" | Notes: ≡ homotypic synonym; = heterotypic synonym
|}
Hybridization of honey locust with water locust (Gleditsia aquatica) has been reported.
Names
The genus Gleditsia is named in honor of Johann Gottlieb Gleditsch, the director of what has become the Berlin Botanical Garden and Botanical Museum. The species name is derived from Greek and means "three thorns". This name comes from the slightly sweet pulp that surrounds the seeds in the tree's pods and their resemblance to the pods of the carob or "locust tree" from the Middle East. Honey locust is also used for the genus as a whole or for other species in it. The first recorded use of the name was in 1709 by John Lawson in his account A New Voyage to Carolina. In the late 1800s honey locust was sometimes used as an alternate name in localized areas for other species such as for mesquit (Prosopis juliflora) in Texas and New Mexico, for black locust (Robinia pseudoacacia) in Minnesota, and for clammy locust (Robinia viscosa) in New York and New Jersey. Variants on this name include "common honey locust", and "thornless honey locust". In South Africa it is called "driedoringboom", driedoring-gleditsia", soetpeulboom", "springkaanboom", or "leoka". In Canada it is a rare forest species found in southern Ontario near Lake Huron, Ontario, or Erie. However, Plants of the World Online (POWO) lists it as introduced to Ontario while NatureServe and World Plants list it as native.
In the eastern United States honey locust trees are regarded as native to Connecticut, Massachusetts, New Hampshire, Rhode Island, and New York.
Worldwide it has become established outside of cultivation in Europe, southern Asia, Australia, southern Africa, and in Argentina and Uruguay. It grows best in soils that are organically rich and moist, but well-drained. However, it is tolerant of a wide range of soil conditions.
The seeds of the honey locust are resistant to sprouting without damage to the seed coat. In controlled experiments only 5% of the seeds sprout without treatment. In comparison, seeds soaked in concentrated sulfuric acid for one and a half hours increased germination to 68% and two and a half hours increases it to 98%.
The honey locust moth (Syssphinx bicolor) feeds on honey locust and Kentucky coffee trees while a caterpillar. The first brood of the moths emerge from hibernation in the ground in the late spring. The green larvae have several horns on the backs and reach full size in about three weeks. When they reach full size they pupate in the soil. There may be two or three broods in a year.
Honey locust trees are a frequent host for the parasitic plant American mistletoe (Phoradendron leucarpum), but usually is not infected by large numbers of them and without suffering obvious damage.
Invasiveness
Honey locust is one of the most successful of the trees and shrubs in the pea family at invading new habitats worldwide. The species is a major invasive environmental and economic weed in agricultural regions of Australia. The plant forms thickets and destroys the pasture required for livestock to survive. The thickets choke waterways and prevent both domestic and native animals from drinking and also harbour vermin. The spines cause damage to both people and domestic and native wildlife and puncture vehicle tyres. In Argentina the trees were introduced in the early 1800s to be used as a landscape ornamental, as a forest tree, and in windbreaks. It escaped from cultivation and has invaded native grasslands, subtropical montane forest (yungas), and woodlands of the Gran Chaco. In other regions of the world, ranchers and farmers who employ monocropping deem honey locust a nuisance weed; its fast growth allows it to out-compete grasses and other crops.
Notable trees
The oldest known tree is one growing in the Kozia Brana Cemetery in Bratislava, Slovakia. It was planted sometime between 1773 and 1793, making it approximately years old. When last measured in 2021 it had a diameter of and a height of .
The largest recorded in the American National Register of Champion Trees is one growing in Botetourt County, Virginia. It was last reported as healthy in 2019. It has a diameter at breast height of about , a height of , and a crown spread of .
Cultivation
Due to the honey locust's tolerance of urban problems such as salt spray, compacted soils, poor aeration, constrained planting areas, and pollution, it has been widely planted in cities. In addition it will adapt to relatively dry conditions and either alkaline or acidic soils. becoming somewhat overplanted in the 1970s. Three insects are the main pests that attack the honey locusts in urban areas, honeylocust plant bug (Blepharidopterus chlorionis), mimosa webworm (Homadaula anisocentra), and honeylocust spider mite (Platytetranychus multidigituli). Thornless cultivars are especially susceptible to damage by the Asian mimosa webworm. Though healthy trees are able to withstand one or two years of complete defoliation, stressed trees may be killed. The number of honey locust trees within increases attacks by the webworms as does the amount of impermeable hardscape surfaces out to from a tree. It was sourced from a then 50-year-old tree in Beatrice, Nebraska by the Inter-State Nursery of Hamburg, Iowa in 1955. This cultivar is shaped similarly to an American elm with a wide, spreading top and is also thornless and nearly pod free. It is a large and vigorous selection with a narrow crown that is thornless and nearly seedless. It was introduced to plant commerce by Princeton Nursery of New Jersey in 1973 and patented in 1958. It is alternatively spelled 'Emerald Cascade' by some sources.
Imperial
It is a popular cultivar that grows to only about in height. It is used where a somewhat smaller shade tree is required. Sources disagree on the maximum height obtained by this cultivar, Purdue lists it as while the University of Florida lists it as .
Skyline
This is a very common cultivar that has a more pyramidal or slightly squared shape to its canopy. The leaflets have a redish to bronze tone when emerging and a dark green and leathery appearance for most of the season. It was introduced by the Cole Nursery in Painesville, Ohio in 1957. and consumed by wildlife and livestock.
Despite its name, the honey locust is not a significant honey plant.
Timber
thumb|Gleditsia triacanthos
Honey locusts produce a high quality, durable wood that polishes well, but the tree does not grow in sufficient numbers to support a bulk industry. However, a niche market exists for honey locust furniture. It is also used for posts and rails because of the dense, rot-resistant nature of the wood. The heartwood of honey locust is reddish brown while the sapwood is pale yellow. It is strong, but has a coarse grain texture.
Nitrogen fixation
The ability of Gleditsia to fix nitrogen is disputed. Many scientific sources state that Gleditsia does not fix nitrogen. Some support this statement with the fact that Gleditsia does not form root nodules with symbiotic bacteria, the assumption being that without nodulation, no nitrogen fixation can occur. In contrast, many popular sources, permaculture publications in particular, claim that Gleditsia does fix nitrogen but by some other mechanism.
There are anatomical, ecological, and taxonomic indications of nitrogen fixation in non-nodulating legumes. Both nodulating and non-nodulating species have been observed to grow well in nitrogen-poor soil with non-nodulating legumes even dominating some sites. The litter and seeds of non-nodulating species contain levels of nitrogen higher than non-legumes and sometimes even higher than nodulating legumes growing on the same site. How this happens is not yet well understood but there have been some observations of nitrogenase activity in non-nodulating leguminous plants, including honey locust.
References
Further reading
External links
- Gleditsia triacanthos images at bioimages.Vanderbilt.edu
- Gleditsia triacanthos images at Forestry Images
- Gleditsia triacanthos at the USDA Plants Database