Conyza ramosissima Cron.

Dwarf Horseweed

Conyza ramosissima plant2

Family - Asteraceae

Habit - Annual taprooted forb.

Stems - Spreading, sometimes with ascending tips, to 25 cm, usually highly branched, conspicuously pubescent with antrorse white hairs, the plant thus appearing canescent.

Conyza ramosissima stem2Stem and nodes.

Leaves - Alternate, simple, entire, sessile, 0.5-2.5 cm long, narrowly linear, moderately to densely appressed-hairy.

Conyza ramosissima leavesStems and leaves.

Inflorescences - short panicles, often dense and well developed but sometimes appearing as short racemes or loose clusters at the branch tips.

Conyza ramosissima inflorescenceInflorescence.

Heads - Radiate but very inconspicuously so. Involucre 1.5-3.0 mm long, narrowly cup-shaped or slightly bell-shaped or urn-shaped. Involucral bracts in 2-4 unequal, overlapping series, narrowly lanceolate to linear, the tip ascending, with a slender to relatively broad, green or brown central stripe, and with relatively slender, thin, pale margins, glabrous or sparsely appressed-hairy. Receptacle flat or nearly so, relatively smooth.

Conyza ramosissima headsFlowering heads.

Conyza ramosissima heads2

Ray flowers - 18-30, pistillate, the ligule pale pink to light purple.

Disk flowers - 3-8, perfect, yellow.

Fruits - Achenes 1.0-1.5 mm long, narrowly oblong in outline, flattened, the angles usually with inconspicuous nerves, the surface usually sparsely to moderately and minutely hairy, light tan to pale grayish brown.

Conyza ramosissima fruitsFruits.

Flowering - May - September.

Habitat - Fields, pastures, prairies, glades, lawns, sidewalks, roadsides, railroads, open disturbed areas.

Origin - Native to U.S.

Lookalikes - None.

Other info. - This low, nondescript species is often missed or ignored. Its appearance is the very antithesis of showy. It occurs throughout Missouri but is probably undercollected. Its distribution beyond Missouri is predominantly within the Midwest. It looks nothing at all like its sibling Conyza canadensis, being low and extensively branched rather than tall and erect, although the flowering heads of the two plants are very similar. A key character for identification is the strongly appressed, forward-pointing white hairs on the stem, which will unambiguously differentiate this species from any specimens of C. canadensis which may have been forced into a low, branched habit due to mowing. These hairs lend a grayish cast to the entire plant.

This species has a bitter taste and is avoided by livestock. It is highly disturbance adapted and can be sometimes be found growing in urban sidewalk cracks and other hostile environments. Another name for the plant is Erigeron divaricatus. Divaricatus means "widely spreading" and ramosissima means "much branched." Both names are highly appropriate.

Photographs taken at the Kansas City Zoo, 7-12-99, and in St. Louis, MO., 7-28-03 (DETenaglia); also near the Missouri Botanical Garden's Monsanto Building, St. Louis, MO, 7-23-2015 (SRTurner).


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