Matricaria discoidea
disc mayweed, matricaire odorante, pineapple weed, rayless chamomile
1–10+, usually erect or ascending, sometimes decumbent, branched from bases.
blades (5–)10–65(–85) × 2–20 mm.
2–25(–30) mm (sometimes villous near heads).
2.5–3.8 mm.
2.5–7.5 mm, ± acute or obtuse.
0.
125–535+;
corollas greenish yellow, 1.1–1.3 mm (± glandular), lobes 4(–5).
29–47+ in 3 series, margins mostly entire.
discoid, (1–)4–50(–300), usually borne singly, sometimes in open, corymbiform arrays.
pale brown to tan, ± cylindric-obconic (asymmetric, abaxially ± gibbous distally), 1.15–1.5 mm, ribs white (lateral 2 each with reddish brown mucilage gland along ± entire length, glands sometimes distally expanded, abaxial 1–2 weak, sometimes each with elongate mucilaginous gland), faces not glandular;
pappi coroniform, entire.
hemispheric to broadly ovoid, 4–7(–11) × 4–7.5(–10) mm.
= 18.
Matricaria discoidea
Matricaria discoidea has been used as a medicinal and aromatic plant by Native American tribes (D. E. Moerman 1998). It also is considered a weed, and it is resistant to a photosystem II inhibitor herbicide in the United Kingdom (www.weedscience.org). It is a northwestern North American native that has spread to eastern and northern North America and elsewhere (E. McClintock 1993b; E. G. Voss 1972–1996, vol. 3; A. Cronquist 1994). NatureServe (www.natureserve.org) and Natural Resources Conservation Service (plants.usda.gov) erroneously present M. discoidea as introduced on the continent. Its natural habitat is ill-defined because the species has become ruderal even in its native range. For discussion of the nomenclature of this taxon, see S. Rauschert (1974); K. N. Gandhi and R. D. Thomas (1991); Cronquist; and Voss.
“Matricaria matricarioides (Lessing) Porter” cannot be applied to the American taxon; M. matricarioides was originally published as Artemisia matricarioides Lessing, a new name for Tanacetum pauciflorum Richardson (see S. Rauschert 1974), itself a synonym of T. huronense Nuttall. W. Greuter (pers. comm.), who accepts M. discodea, considers Rauschert’s treating Artemisia matricarioides as homotypic with T. pauciflorum as equivalent to a lectotype designation.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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