Disc Mayweed

Foodplant / sap sucker
Brachycaudus helichrysi sucks sap of Matricaria discoidea

In Great Britain and/or Ireland:
Foodplant / parasite
sporangium of Paraperonospora leptosperma parasitises live Matricaria discoidea

Foodplant / parasite
Podosphaera fusca parasitises live 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.

Annuals, (1–)4–40(–50) cm; aromatic (pineapple odor when bruised). Stems 1–10+, usually erect or ascending, sometimes decumbent, branched from bases. Leaf blades (5–)10–65(–85) × 2–20 mm. Heads discoid, (1–)4–50(–300), usually borne singly, sometimes in open, corymbiform arrays. Peduncles 2–25(–30) mm (sometimes villous near heads). Involucres 2.5–3.8 mm. Phyllaries 29–47+ in 3 series, margins mostly entire. Receptacles 2.5–7.5 mm, ± acute or obtuse. Ray florets 0. Discs hemispheric to broadly ovoid, 4–7(–11) × 4–7.5(–10) mm. Disc florets 125–535+; corollas greenish yellow, 1.1–1.3 mm (± glandular), lobes 4(–5). Cypselae 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. 2n = 18. [as M. matricarioides]

Chamomilla suaveolens (Pursh) Rydberg; C. discoidea (de Candolle) J. Gay ex A. Braun; Santolina suaveolens Pursh 1813, not Matricaria suaveolens Linnaeus 1755

Chamomilla suaveolens (Pursh) Rydberg
Santolina suaveolens Pursh, Fl. Am. Sept. 520. 1814.
Artemisia matricarioides Less. Linnaea 6: 210. 1831.
Colula matricarioides Bong. Mem. Acad. St.-Petersb. VI. 2: 147. 1832.
Tanacelum suaveolens Hook. Fl. Bor. Am. 1: 327. 1833.
Matricaria discoidea DC. Prodr. 6: 50. 1837.
Tanacetum pauciflorum DC. Prodr. 6: 131. 1837. Not T. paiiciflorum Richards. 1823.
Matricaria tanacetoides Fisch. & Mey. Ind. Sem. Hort. Petrop. 7: 52. 1840.
Lepidanlhus suaveolens Nutt. Trans.' Am. Phil. Soc. II. 7: 397. 1841.
Ceuocline pauciflora C. Koch, Bot. Zeit. 1: 41. in part. 1843.
Lepidotheca suaveolens Nutt.; T. & G. Fl. N. Am. 2: 413, as synonym. 1843.
Tanaceiuyn matricarioides Less.; Ledeb. Fl. Ross. 2: 544. as synonym. 1846.
Akylopsis suaveolens Lehm. Ind. Sem. Hort. Hamb. 1850: 3. 1850.
Chamomilla discoidea J. Gay; A. Br. Bot. Zeit. 10: 650. 1S52.
Matricaria matricarioides Porter, Mem. Torrey Club S: 341. 1894.
Matricaria suaveolens Buch. Fl. Brem. ed. 4. 142. 1894. Not M. suaveolens L. 1755.
A leafy annual; stem !-3 dm. high, striate, branched, glabrous; leaves 2-4 cm. long, glabrous, bior tri-pinnatifid into short linear-filiform divisions; heads numerous, discoid; involucre saucer-shaped, 3 mm. high, 5-8 mm. broad; bracts in 2-3 series, subequal, elliptic, rounded at the apex, with white, scarious margins; receptacle conic, hollow; ray-flowers wanting; disk-corollas greenish-yellow, 1.5 mm. long; tube slightly longer than the campanulate throat; lobes 4, ovate; achenes greenish-brown, oblique, with 4 ribs on the inner side, smooth on the back and between the ribs; crown of the pappus minute or obsolete.
Type locality; Banks of the Kooskoosky [Clearwater River, Idaho).
Distribution: Native from Alaska to Montana, Arizona, and Lower California; naturalized eastward to Newfoundland, New Jersev, and Missouri; also in eastern Siberia; adventive in Europe.

Matricaria discoidea, commonly known as pineappleweed, wild chamomile, disc mayweed, and rayless mayweed, is an annual plant native to northeast Asia where it grows as a common herb of fields, gardens, and roadsides. It is in the family Asteraceae. The flowers exude a chamomile/pineapple aroma when crushed. They are edible and have been used in salads (although they may become bitter by the time the plant blooms) and to make herbal tea.