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Saturday, July 20, 2013

Gleditsia triacanthos 'Inermis' - Thornless Honey Locust

The thornless honey locust is a deciduous fast growing medium to large tree with an open spreading crown growing to 40 feet or more.

Decent but not great fall color. One of the first trees to go dormant and one of the last to leaf out, what a slacker.

The foliage is alternate, pinnately or bi-pinnatley (sometimes on the same leaf) compound, 6-10" long. Leaflets are small, about an inch long and half that wide with crenate margins. Medium to dark green in color. 

Bipinnately compound leaf below.

Like many in the pea family they have a swollen petiole base called a pulvinus.

Leaflets are small, 1" x 1/2" with crenate margins.

Stems are greenish-brown, zig-zag, and have swollen nodes. No terminal bud. Actually called a pseudoterminal bud. You can see the stub below. At some point the plant stops growing and the stem dies back to some bud rather than forming a true terminal like many plants.

Plants are monoecious resulting in male and female plants (however like Jurassic Park some flowers will find a way to have all the parts.) Flowers not showy. Males in 2" long clusters, females in few flowered clusters.

The cultivated cultivars are from the variety inermis, which means no thorns, but I love thorns. Have a look at these. The specific epithet is triacanthos meaning three parted thorn. What a cool tree with thorns.  

Fruit is a large pod, green turning dark brown. Very twisted and very hard. We don't seem the very often as all the cultivars planted and grown are males.  'Sunburst' is a popular cultivar with golden foliage, I can't identify any of the others by sight.  

With so many trees with pinnately compound leaves they all look alike to my students. Several keys, small crenate margins on the leaflets, the stems are zig zag and quite often you will find both pinnnate and bipinnate leaves on the same tree, often the same branch.

Soquel Dr across from Twins Palms Dr

Santa Cruz 
River St. In the parking lot at the Patagonia Outlet Store
Front St. across from Trader Joes is a long line of them.

Scotts Valley
Shopping center at corner of Mt Hermon Dr and Graham Hill.

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