1.
Matricaria discoidea
de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 6: 50. 1838.
Pineappleweed, disc mayweed, rayless chamomile, matricaire odorante
Chamomilla suaveolens
(Pursh) Rydberg;
C. discoidea
(de Candolle) J. Gay ex A. Braun;
Santolina suaveolens
Pursh 1813, not
Matricaria suaveolens
Linnaeus 1755
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.
2
n
= 18. [as
M. matricarioides
]
Flowering early summer—fall. Open areas, bare disturbed areas and rural or urban waste grounds, sometimes alkaline, roadsides, railroads, footpaths, cultivated and abandoned fields and gardens, irrigation ditches, stream banks, sandbars; 0—2700 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Kansas, Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; introduced in Eurasia, Australia.
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.
