Ostrya knowltonii (Western Hop Hornbeam)
Betulaceae (Birch Family)

Semi-desert. Wet, shady, canyon bottoms of Southeast Utah and Northern Arizona. Spring.
Behind the Rocks Wilderness Study Area, Utah, April 23, 2006.

Western Hop Hornbeam is a rare tree, found only in a small area of southeastern Utah, northern Arizona, and four scattered areas of southwestern New Mexico, and far western Texas.  It is prominent on the Chesler Park Trail of Canyonlands National Park as hikers walk through the narrow Breezeway before descending into Elephant Wash and it is sometimes quite abundant in moist, rocky canyon bottoms around Moab, Utah. 

It typically grows to a maximum of 10-30 feet tall and 6-15 inches in diameter often with several main trunks and often in close proximity to a number of other Ostrya knowltonii.  The tree is prominent because of its cracked and shredded bark, hop-like seed pods, and male pollen-bearing catkins.  (See the photographs below.)

"Ostrya" is Greek for "hardwood tree" and recognizes the dense wood of the Hop Hornbeams (Western and Eastern) which gives them another common name, "Ironwood".   Botanist Frank Knowlton (1860-1926) discovered the tree in 1889 below the rim of the Grand Canyon.  (More biographical information.)

Ostrya knowltonii (Western Hop Hornbeam)
Betulaceae (Birch Family)

Semi-desert. Wet, shady, canyon bottoms of Southeast Utah and Northern Arizona. Spring.
Behind the Rocks Wilderness Study Area, Utah, April 23, 2006.

In the picture at left, the maturing seed pods on the female catkins resemble those of hops (various vine Humulus species which are used to flavor beer).  The dried male pollen-bearing catkin is in the center of the left picture.

Since each tree has both male and female flowers, the tree is termed "monoecious", in contrast to "dioecious" species which have male and female flowers on separate plants.

Ostrya knowltonii (Western Hop Hornbeam)
Betulaceae (Birch Family)

Semi-desert. Wet, shady, canyon bottoms of Southeast Utah and Northern Arizona. Spring.
Behind the Rocks Wilderness Study Area, Utah, April 16, 2008.

These long fresh male pollen chains have just opened and tiny stamens protrude. 

Ostrya knowltonii (Western Hop Hornbeam)
Betulaceae (Birch Family)

Semi-desert. Wet, shady, canyon bottoms of Southeast Utah and Northern Arizona. Spring.
Behind the Rocks Wilderness Study Area, Utah, April 23, 2006.

Bark on younger trees is gray, with darker, slightly raised, longitudinal ridges. Mature bark is shredded, as shown in the photograph below of a five inch diameter trunk.

Ostrya knowltonii (Western Hop Hornbeam)
Betulaceae (Birch Family)

Semi-desert. Wet, shady, canyon bottoms of Southeast Utah and Northern Arizona. Spring.
Behind the Rocks Wilderness Study Area, Utah, April 23, 2006.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Ostrya knowltonii