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Frangula obovata
 

 

Frangula obovata. Synonyms: Frangula betulifolia subspecies obovata, Rhamnus betulifolia (Pearleaf Buckthorn)
Rhamnaceae (Buckthorn Family)

Semi-desert. Rock crevices. Spring.
Above: Butler Wash, Utah, May 21, 2014 and left, Canyonlands National Park, Utah, Confluence Trail, May 20, 2004.

Pearleaf Buckthorn often grows out of crevices in rocks otherwise bare of noticeable vegetation.  Such Buckthorns thrive on moisture and nutrients that wash over the rocks and filter through the porous sandstone.  In deeper soils of Canyon Country, Buckthorn typically grows three to five feet high and wide, twisting and drooping in an open pattern.  Given sandy conditions near a stream or at the base of rocks (as in the top photograph and the autumn photograph below), it grows to nine feet tall and wide with stems to several inches in diameter.

"Rhamnos" is a classical Greek name given this genus by Linnaeus in 1753; "betulifolia" means "Birch-like foliage"; and "obovata" refers to the sometimes reverse egg-shape of the leaves. Edward Greene named the Rhamnus betulifolia species in 1896.

Kearney and Peebles named Rhamnus betulaefolia var. obovata from a collection that Peebles and Smith made on Navajo Mountain in Arizona in 1938.

Kartesz and Gandhi renamed this taxon Frangula betulifolia subsp. obovata in 1994.

The Frangula genus was named by in 1768 by Philip Miller. Miller separated Frangula from Rhamnus on the basis of floral characteristics and although that distinction has been controversial over the centuries, it is now widely accepted. "Frangula", from the Latin "frang", "to break", refers to the brittle wood.

In 2009 Nesom and Sawyer concluded that Frangula betulifolia and Frangula betulifolia subspecies obovata were distinct enough in morphological characteristics and geography to warrant independent species status.

According to Kearney and Peebles (1960, p. 532), “The typical plant [of Frangula betulifolia], with elliptic or oblong leaves, is limited in Arizona to the south-central and southern counties. In the northern part of the state is found var. obovata Kearney & Peebles, the type of which was collected on Navajo Mountain, Coconino County. This variety is apparently common in and near the Grand Canyon and Havasu Canyon, and extends into southern Utah and Nevada, thus being well separated geographically from the main area of R. betulifolia. The variety is characterized by more or less obovate leaves with thicker, more prominent veins.”

The current study corroborates the observations of Kearney and Peebles.... In view of their morphological and geographic distinction, recognition of each at specific rank is appropriate.

From the description by Nesom and Sawyer:

Frangula betulifolia:   Leaf blades elliptic to oblong, elliptic-ovate, or narrowly ovate, 1.6–2.6(–2.9) times longer than wide, relatively thin or slightly thickened, paler beneath, lateral veins (8–)9–13 pairs.

Flowering Apr–Jun. Cliff bases, ledges, moist canyons, ridges, roadsides, rocky slopes, stream banks, Gambel’s oak, oak-pine, pine-walnut-maple, white fir; 900–2750 m. Ariz., N.Mex., Tex.; Mexico (Chihuahua, Coahuila, Durango, Nuevo León, Sonora, Tamaulipas).

Frangula obovata:  Leaf blades obovate to oblong-obovate or oblong, 1.2–1.8(–2.5) times longer than wide, distinctly thickened and nearly coriaceous, evenly colored on both surfaces, lateral veins (5–)6–8(–9) pairs.

Flowering Apr–Jun. Canyon bottoms, cliff faces, stream and creek banks, hanging gardens, talus, seepage below cliffs; 1350–2350 m. Ariz., Colo., Nev., Utah.  

The report in Nesom and Sawyer and in the map below that Frangula obovata is found in La Plata County, Colorado is not supported by any collected specimens and is almost certainly in error. I have searched the area at Fort Lewis College, Durango, where the Frangula was supposedly found, and there is no suitable habitat and no sign of any Frangula.

Frangula obovata. Synonyms: Frangula betulifolia subspecies obovata, Rhamnus betulifolia. (Pearleaf Buckthorn)
Rhamnaceae (Buckthorn Family)

Semi-desert. Rock crevices. Spring.
Canyonlands National Park, Utah, May 20, 2004.
Corona Arch Trail, Utah, June 7, 2007.

Tiny yellow-white-green flowers are borne in leaf axles in mid-spring and then crisp little seed pods follow.

                                       

Frangula obovata

Frangula obovata. Synonyms: Frangula betulifolia subspecies obovata, Rhamnus betulifolia(Pearleaf Buckthorn)
Rhamnaceae (Buckthorn Family)

Semi-desert. Rock crevices. Spring.
Upper Mule Canyon, Utah, October 23, 2006 and
Canyonlands National Park, Utah, November 11, 2005.

Autumn colors range from golds to lemons.

                                        

 

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

Frangula betulifolia

Range map for Frangula betulifolia

Frangula obovata

Range map for Frangula obovata