- Latin synonym: Tripleurospermum perforatum, Matricaria inodora, Matricaria perforata, Tripleurospermum maritimum ssp. inodorum
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Annual, often overwintering herb.
- Height: 20–80 cm (8–32 in.). Usually 1-stemmed. Stem erect–ascending, branching, glabrous, green.
- Flower: Single flower-like, usually 3–5 cm (1.2–2 in.) capitula, surrounded by involucral bracts. Capitula’s ray-florets white, tongue-like, tip shallowly 3-toothed; disc florets yellow, tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucral bracts different lengths, 1–1.5 mm (0.04–0.06 in.) broad, light brown–white margins. Disc stacked, full. Capitula 1–20 borne in a corymbose cluster.
- Leaves: Alternate, short-stalked–stalkless. Blade 2–3 times pinnately lobed (–with leaflets), glabrous, lobes (or leaflets) long, thread-like narrow, sharp-pointed.
- Fruit: Flattish, ridged achene, with 2 round–angular oil spots, tip sometimes with small, membranous ring.
- Habitat: Fields, fallow land, lawns, wasteland, roadsides, yards, gardens.
- Flowering time: June–October.
Scentless mayweed’s flower smells quite unpleasant to the human nose, but the plant’s pollinators would appear to hold a different opinion and its capitula attracts a host of different flies, bees and bumblebees. Pollination often gives a good result, and plants are quite able to produce tens of thousands of seeds. The record for a cypsela is a whopping 1,650,000! Despite efficient reproduction the species has only become abundant and noticeably spread in recent decades as the achenes have no flying hairs. Scentless mayweed became more common with the beginning of hay cultivation as its seeds would spread with Timothy-grass and clover, which have same-sized achenes. The seeds remain viable in the earth for years and a fair number survive the journey through a plant-eating animal’s digestive tract – although cattle would in any case appear to avoid eating the plant. Additionally, the plant is quite resistant to some weed-killers.
Scentless mayweed is a rare weed in crop fields and, although it is a little more common in hay fields, it is more commonly found in fallow fields, waste ground, newly sown lawns and roadsides that have been recently dug up. It also likes potato fields, vegetable patches and other similar culturally-influenced land. Scentless mayweed is sometimes called oxeye daisy in Finnish but the species are quite different and not easily confused: oxeye daisy’s leaves are entire while scentless mayweed’s are very finely lobed. The eye is usually drawn to the capitula, however, which look alike, and scentless mayweed has only recently become more common as oxeye daisy has become rarer.
Scentless mayweed grows on damp slopes on arable land and waste ground in central Finland, and its place is taken in northern Finland by the other sea mayweed subspecies T. maritimum spp. subpolare. This pair look so alike that the involucral bracts have to be examined to make a positive identification. Scentless mayweed’s involucral bracts narrow towards the tip and have a pale and narrow membranous margin, while the membranous margin on the broad, blunt involucral bracts of spp. subpolare is dark and wide. Scentless mayweed is also like scented mayweed (Matricaria chamomilla), and the best way to tell them apart is by the disc. On scentless mayweed it is initially shallowly conical, gradually changing to become semi-spherical, but it is not high-stacked and remains always full (on scented mayweed hollow). As their names suggest, there is also a clear difference in fragrance: scented mayweed has a pleasant aroma while scentless mayweed’s is almost absent.