Populus

Trees and Shrubs of Kern County (Jan 2013)

Key to species of Populus

1. Leaves at least 2× longer than wide....................................... Populus angustifolia

1. Leaves1–1.5× longer than wide................... ........... ............................................. 2

2. Lateral (secondary) veins of leaves forking near mid region,
sometimes repeatedly forked before reaching margin; leaves
about as long as wide, often broadly notched along base;
petioles flattened... ....................... .......................................... Populus fremontii

2. Lateral (secondary) veins forking more near margin; leaves
often ~1.5× longer than wide, not to slightly notched at base;
petioles round...................................................................... Populus trichocarpa

Populus angustifolia E. James 1823. Narrow-leaved cottonwood. Tree to 15 m with long slender straggly branches, or willow-like shrubs in Kern Co.; twigs reddish brown, lenticillate, branches with whitish gray bark and mostly smooth when young, becoming brown and deeply furrowed with age; leaves deciduous, alternate, narrowly elliptical to somewhat heart-shaped (no notch at base), sharply serrated along margins; flowering Apr–May. Stream-banks, flood plains, and slopes in mountains, 4,500–9,600 ft; Nebraska to northern Chihuahua Mexico, west to central Idaho, southeastern Oregon, Nevada, Arizona, New Mexico. Generally rare in California, known from Division Creek, Inyo Co. Other specimens from Inyo County reportedly identified P. angustifolia are considered Populus trichocarpa, while others from the San Bernardino Mts. and Kern Co. have yet to be studied. Type collected along the upper part of the Platte River, near the rocky Mts. [on the south Platter River near Brighton, Adams Co., CO], Kern Co.: Twisselmann reported it “common along the Kern River above Kernville, mostly in a shrubby form, possibly caused by repeated breakage in times of high water.” CCH includes one specimen reported from “Keane.” Also occurring as a shrub in Kern River Canyon 23 miles east of Bakersfield along seasonally wet north-facing rocky ravine, ~2,800 ft (pers. obs., image shown here), and is clearly related to P. angustifolia by the short petioles and “lanceolate leaves”. CalPhotos include images of plants in the San Bernardino Mts. The shrub form may prove to be a distinct variety with notable disjunct occurrences.

Populus fremontii S. Watson 1875 ssp. fremontii. Fremont's cottonwood. Tree up to 30 m, old bark furrowed with whitish brown flattened ridges between the furrows; twigs yellowish; leaves broadly heart-shaped, shallowly lobed along margins; flowering Mar–Apr; fruiting branches hanging with many capsule fruits. Type from Deer Creek, at “Lassens” [near Vina] on the upper Sacramento, Tehama Co., CA. Common along streams in California. Fremont cottonwood forest recognized in MCV2 when >50% relative cover, or 5% absolute cover, in tree layer, or 30% relative cover in tree layer if Salix species codominate. Kern Co.: “Common in moist, sometimes somewhat alkaline soil from the valley floor to the Douglas oak woodland and in the desert-facing canyons of the mountains” (Twisselmann). Populus fremontii-Salix gooddingii Woodland Alliance proposed (Magney 2010) in the Tejon Ranch Conservancy (Old Headquarters, Bi-Centennial).

Populus trichocarpa Torrey & A. Gray ex Hooker 1852. Black cottonwood. Tree to 60 m, bark grayish, furrowed in age, leaves heart-shaped but sometimes truncated at base, or merely rounded but not notched; serrated along margins; flowering Feb–Apr. Along streams in most of California, from near sea level to above 9,000 ft. Type from Santa Clara River near Buenaventura, Ventura Co., CA. Kern Co.: An extensive colony for nearly a mile in Tejon Canyon from 3,000 to 3,600 ft, and from a single very large tree in upper El Paso Canyon, and also reported that Charlotte Smith found a few black cottonwoods along Bull Run Creek in the northern Greenhorn Range (Twisselmann).