- Latin synonym: Matricaria matricarioides, Matricaria suaveolens
- Name also: Pineapple Weed, Pineapple-weed, Rayless Mayweed, Wild Chamomile, Disc Mayweed
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Annual herb.
- Height: 5–30 cm (2–12 in.). Stem usually abundantly branching from top, glabrous–short-haired at top, dirty green, quite fleshy. Strong herb-like fragrance.
- Flower: Flowers Single flower-like approx. 5–9 mm (0.2–0.36 in.) capitula surrounded by involucral bracts. Capitula’s ray-florets lacking; disc florets lime green, tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucral bracts linear–elliptic, round-tipped, edges with broad membranous margins. Disc narrowly stacked, hollow. Capitula usually borne in a corymbose cluster.
- Leaves: Alternate, short-stalked–stalkless. Blade 2–3 times densely pinnately lobed–with leaflets. Lobes or leaflets almost linear, thicket, terminated by a short bristle.
- Fruit: Light brown, 3–4-ridged, 1.2–1.5 mm (0.48–0.6 in.) long achene, tip with shallow, pale, crown-like membranous ring (pappus).
- Habitat: Yards, gardens, paths, roadsides, cracks in the pavement, fields, wasteland, rubbish tips, fields, shores.
- Flowering time: July–September(–October).
Pineapple mayweed that can be found growing in every yard in Finland can trace its roots back to either north-east Asia or western North America. The species travelled to Europe in the middle of the 19th century. Plants began to be cultivated in botanic gardens as exotic new foreign species with different names until they escaped the gardener’s clutches. The species seems to have started out in Finland in much the same way: to our knowledge the first pineapple mayweed in Finland was grown in Kaisaniemi botanic garden in Helsinki in 1849, and it was classed as a mutation of scented mayweed. A year later it had already spread both west and east to Turku and Lappeenranta, and in less than 100 years it was in yards and on banks and waste ground all around Finland.
Pineapple mayweed’s trump card is the speed of its annual cycle: from seed to seed in less than 100 days. Each achene contains a good 5,000 seeds, and they germinate well. The achenes are very small and light: seven million of them would be required to make a kilo. They are sticky when wet and spread easily with passers-by, on shoes and with pets, and their small size lets them go unnoticed. Its spread is further helped by its durability: tough-stemmed pineapple mayweed can take a lot of abuse and rough handling. It is no wonder then that it is often the first to turn up in habitats that have recently been stripped of its vegetation, and it has colonized all the habitats that have a similar climate to its Pacific coast homeland, from Greenland to New Zealand. Pineapple mayweed continues to spread in Finland into more marginal habitats around wilderness huts and camp sites on hiking boots, and to the outer bird rocks of the archipelago with the birds.