Annuals, 15-50+ cm; internodes mostly 15-30+ mm. Leaf blades oval or elliptic to obovate, 15-35+ × 8-25+ mm. Phyllaries 5, linear, 15-25+ mm. Florets mostly 30-50+; corollas greenish to purplish, 9-12.5 mm. Cypselae 9-12 mm; pappi: longer bristles 7-10 mm. 2n = 22. Flowering late summer-fall. Ephemerally wet sites in desert mountains; 1000-1500 m; Ariz., N.Mex., Tex.; Mexico; West Indies (Antilles); Central America; South America.
Kearney and Peebles 1969, McDougall 1973, Shreve and Wiggins, 1964
Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Herbaceous annuals, to 1 m tall, herbage glabrous, with translucent oil glands. Leaves: Opposite below, alternate above, broadly oval to obovate, petiolate, thin, pale green, weakly sinuate, with conspicuous transparent oil glands along the margins. Flowers: Heads discoid, disk corollas white with purple throats and lanceolate lobes, perfect, the receptacle naked, involucres cylindric to turbinate, phyllaries linear, equal, 5-9, in a single series, with 2 rows of oil glands, the heads solitary at branch tips. Fruits: Achenes dark brown or black, slender, elongate, angled, striate, and hispidulous, 12-13 mm long. Pappus of numerous scabrous, capillary bristles; flowering August-October. Ecology: Rocky canyons, slopes, and outwash fans; 3,500-5,000 ft (1067-1524 m) Distribution: Arizona; Mexico. Notes: Distinguished first by the strong scent emitted from the crushed plant, especially under your feet when tromping through abundant stands. It is an erect annual with broad, ovate leaves with shallow lobes, the heads are also distinct, being of fused phyllaries, which become constricted at the top, forcing a poof of stigmas resembling a mohawk. This species has 52 synonyms! In the common older texts of the southwest, look for it under Porophyllum macrocephalum. Differentiate this species from P. gracile by the annual plants, oval to obovate, thin, green leaves, and apically thickened peduncles of P. ruderale. P. gracile has linear to filiform leaves, perennial habit, woody bases, and non-thickened peduncles. Ethnobotany: Unknown Etymology: Porophyllum is from Greek poros, a passage or pore, and phyllon, leaf, a reference to the translucent glands on the leaf, while ruderale means growing in waste places. Synonyms: Porophyllum ruderale subsp. macrocephalum Editor: LCrumbacher 2011, FSCoburn 2015
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