Tripleurospermum is a genus of flowering plants in the family Asteraceae, placed in the tribe Anthemideae (the chamomile tribe) within the order Asterales. The genus was described by Carl Heinrich Schultz Bipontinus (Sch.Bip.) in 1844. Commonly known as mayweeds, the roughly 40 recognised species are annual or perennial herbs distributed mainly across Europe and temperate Asia, with a smaller number of species native to North America and North Africa.
Plants in the genus are characterised by finely divided, lobed leaves composed of one to three opposite pairs of segments cut nearly to the midrib, giving them a feathery appearance. The flower heads bear white ray florets surrounding a yellow disc, superficially resembling chamomile or ox-eye daisy flowers. The most distinctive morphological feature is the fruit: an indehiscent, one-celled achene with three prominent ribs and two resinous glands at the base. This combination of characters distinguishes Tripleurospermum from the closely related genus Matricaria, whose fruits lack the three ribs and paired glands.
The genus is most closely allied to Matricaria, Heteromera, and Pyrethrum, and the boundaries between Tripleurospermum and Matricaria have long been disputed — some taxonomic treatments place all or most Tripleurospermum species within Matricaria. The type species is Tripleurospermum inodorum (L.) Sch.Bip., the scentless mayweed, which is now widely naturalized across North America, New Zealand, and other temperate regions, where it is regarded as a noxious agricultural weed. Another well-known member is Tripleurospermum maritimum, the sea mayweed, which occupies Arctic and sub-Arctic coastlines of both Eurasia and North America.
Etymology
The genus name Tripleurospermum derives from the Greek tri- (three), pleuron (rib or side), and sperma (seed), referring to the three-ribbed fruits that are a defining character of the genus.
Distribution
Tripleurospermum species occur mainly in Europe and temperate Asia, with a centre of diversity in Turkey, the Caucasus, and south-western Asia. A smaller number of species extend into North Africa and North America. T. maritimum (sea mayweed) is found along Arctic coasts of both Eurasia and North America, and T. subpolare occurs across Scandinavia and the Baltic region. T. inodorum (scentless mayweed) has been widely introduced outside its native Eurasian range and is naturalised in North America, New Zealand, and elsewhere, where it frequently colonises arable land and roadsides.
Ecology
Several species, notably Tripleurospermum inodorum, are pioneer plants of disturbed ground, thriving in arable fields, roadsides, and waste places. T. inodorum is considered a noxious agricultural weed in parts of North America. T. maritimum is adapted to coastal habitats including shingle beaches, cliff tops, and tidal margins along Arctic and sub-Arctic shores.
Taxonomy Notes
Tripleurospermum was established by Carl Heinrich Schultz Bipontinus (Sch.Bip.) in 1844 in his work Tanaceen (Tanacet. 31). The type species is Tripleurospermum inodorum (L.) Sch.Bip. Several synonymous genera have been applied to parts of this group, including Rhytidospermum, Dibothrospermum, Gastrosulum, Trallesia, and Chamomilla Godr. The genus is closely related to Matricaria, Heteromera, and Pyrethrum, and some authors treat Tripleurospermum species as members of Matricaria; GBIF recognises the genus as accepted within Asteraceae.
