Annuals, 10-150 cm. Leaf blades: bases ± clasping, faces usually both hirtellous to villous and ± gland-ular-viscid; proximal broadly spatulate to oblong, 20-50 × 10-20 mm, obscurely lobed or coarsely toothed; distal oblong to elliptic, 10-20 × 3-10 mm, coarsely toothed from near bases or entire. Heads in racemiform-paniculiform arrays. Involucres 2.5-3+ mm. Receptacles 2-3 mm diam. Pistillate florets 60-100+; corollas: lengths ± 1 / 2 styles, laminae 0. Disc florets 5-20. Cypselae pale tan, 0.5-1 mm, glabrous or sparsely strigillose (hairs 0.05-0.1 mm), sometimes stipitate- or sessile-glandular; pappi fragile or readily falling, of 10-30 whitish bristles in 1 series, (2.5-)3.5-4 mm. 2n = 18.
Flowering year round, mostly fall. Stream banks, roadsides, other disturbed sites, clays or sands, often alkaline soils; -60-1800 m; Ariz., Calif., Colo., Nev., N.Mex., Tex., Utah; Mexico.
J. M. Kingsbury (1964) reported Laënneciacoulteri (as Conyza coulteri) to be toxic to livestock.
FNA 2006, Wiggins 1964, Kearney and Peebles 1969, Heil et al. 2013
Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Annual herbs, 10-100 cm tall, from a taproot; stems glandular or covered with sticky hairs which resemble spider's webs (arachnoid). Leaves: When plant is young, leaves form a densely hairy basal rosette; after plant bolts, the leaves are alternate along the stem, mostly sessile and clasping; blades oblong, 2-5 cm long and 5-15 mm wide, many of them are irregularly toothed, especially near the base. Flowers: Flower heads small, whitish, disciform, arranged in a cylindric or broader panicle; involucres turbinate, 3 mm diameter, the bracts (phyllaries) in 2-5 series, with narrow hyaline margins; 60-100 pistillate florets ring the edges of the flower head in several series, these have whitish corollas and lack ligules (ray petals); disc florets 5-20 per flower head, whitish. Fruits: Achenes less than 1 mm long; topped with a pappus of 10-30 fragile and easily deciduous whitish bristles. Ecology: Found in ditch banks, dry stream-beds and disturbed sites, from 1,500-9,000ft (500-2743 m); flowers September-October. Distribution: CA, s NV, s UT, CO, AZ, NM, w TX; south to c MEX. Notes: An annual that can get quite tall and can be weedy; often very sticky-glandular with clasping, toothed leaves and small white flower heads surrounded by green phyllaries. Similar to its congener L. schiedeana but that species has leaf margins with small teeth, lobes, or no teeth (L. coulteri has larger coarser teeth); narrower leaves 2-8 mm wide (5-15 mm wide in L. coulteri); and the pistillate florets in the flower heads have ligules (i.e. ray petals, which L. coulteri lacks). Ethnobotany: Unknown Etymology: Laennecia is from the Greek lenos, for wooly hair, referring to the hairs covering the leaves and stems; coulteri is named for John Merle Coulter (1851-1928) an American botanist. Synonyms: Conyza coulteri Editor: SBuckley 2010, FSCoburn 2014, AHazelton 2017