American burnweed

not listed

NNR - Unranked

SNR - Unranked

not listed

FACU - Facultative upland

FAC - Facultative

FACU - Facultative upland

American burnweed is a common and widespread, mildly weedy, annual forb. It occurs in the United States east of the Great Plains, in adjacent Canadian provinces, in Mexico, and in Central and South America. Its range in the United States is restricted to about the limits of the eastern deciduous forest. It is common in the eastern half of Minnesota. It grows in light shade to full sun usually in moist areas, sometimes in dry or rocky areas. It is found in woodland openings, power lines, railroads, roadside ditches, and disturbed areas. It is often one of the earliest plants to become established in recently burned sites, hence the common name.

American burnweed rises usually on a single stem, sometimes two or more stems, from a taproot and tufts of fibrous roots. The stem is erect, round, 2′ to 8′ tall, and usually unbranched below the inflorescence. It is dry, not succulent, and is lined with fine vertical ridges. It may be hairless or moderately and unevenly covered with coarse, more or less spreading hairs. At the base of the stem there is a radiating group (rosette) of leaves.

Basal and lower stem leaves are on short stalks (petioles) and are often withered or absent at flowering time. Stem leaves are alternate. Lower and middle leaf blades are elliptic to narrowly egg-shaped, 2⅜″ to 8″ long, and ¾″ to 3″ wide. They are tapered at the base to the petiole and tapered to a sharp point at the tip. The margins are sharply toothed and occasionally shallowly and irregularly lobed. The upper surface is hairless or has scattered coarse hairs. The lower surface is hairless to moderately hairy. The leaves become shorter, narrower, more deeply lobed, and on shorter petioles as they ascend the stem. Upper leaves are stalkless and sometimes partially surround (clasp) the stem at the base. The leaves are dry, not succulent.

The inflorescence is a rounded or elongated arrangement two to twenty ⅓″ to ⅔″ long flower heads in a branched cluster (panicle) at the end of the stem and smaller panicles in the upper leaf axils. Each flower head is subtended by 1 to 6 minute, green, ascending and inward-curved modified leaves (bractlets). The whorl of bracts (involucre) at the base of the flower head is smooth, cylinder-shaped, ⅜″ to ⅝″long, 3 ⁄16″ to 5 ⁄16″wide, and conspicuously expanded at the base. It consists of usually 21 bracts (phyllaries) in two series. The outer series of 4 to 7 phyllaries are minute and entirely green. The inner series of 9 to 15 phyllaries are erect, lance-shaped to linear, flat above, and mostly green but with thin, dry margins that are not green. There are 10 to 100 outer female (pistillate) disk florets and no ray florets. The pistillate florets are ⅜″ to ⅝″long, tubular, thread-like, and whitish to pale yellow. Each one has 4 or 5 erect, triangular lobes. There are also 10 to 20 or more inner florets, most having both male and female parts (perfect), some having just male parts (staminate). The inner florets are whitish to pale yellow or pinkish, and have erect to spreading, narrowly egg-shaped lobes.

The fruit is a dry, brown or purple, 1 ⁄16″ to ⅛″ long (2 to 3 mm) seed capsule (cypsela).

2′ to 8′

Whitish to pale yellow

Moist to dry. Woodland openings, power lines, railroads, roadside ditches, and disturbed areas. Light shade to full sun.

July to October

Sources

2, 3, 4, 5, 7, 22, 24, 28, 29, 30.

Native

Common and widespread

Pilewort

Location: Albany, NY

Location: Cass County