Buttonweeds
What are they?
The buttonweeds are a group of small and perhaps easily overlooked species that are members of the daisy family (Asteraceae). They are species that mostly evolved in the southern hemisphere and look rather different to our native plants, but closer inspection reveals features common to the daisy family. The button-like flowerheads are typical of the family in consisting of a flat disk upon which sits a mass of small, tightly packed, yellow florets, with the whole surounded beneath by small, green bracts called phyllaries. This arrangement is just like that of our Common Daisy and all that is missing is the ring of narrow, white petals (or ligules) around the outside.
Where are they found?
These species are relatively new arrivals to our region and are thus still rather uncommon. However, Yellow Buttonweed favours open ground in wetlands, while other species are appearing as urban weeds in pavement cracks or where spreading out vegetatively from neighbouring gardens.
Identification
Buttonweeds are low growing plants, often with creeping stems that root in at the nodes. They have pinnate or deeply lobed leaves and tiny flowers carried in tight, button-like heads. The species can be told apart fairly easily by flower colour, combined with details of the leaf shape and hairiness.
Yellow Buttonweed Cotula coronopifolia
Of uncertain origin but probably native to the southern hemisphere. A recent introduction to East Anglia, possibly from Europe where it is long-established as an invasive species. Becoming established in coastal grazing marshes in Norfolk and scattered elsewhere. Flowers July to August. Flowerheads relatively large for this group, growing up to 12mm in diameter; leaves with bases sheathing the stems and the whole plant is slightly succulent.
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Annual Buttonweed Cotula australis
Introduced to the UK from Australia and New Zealand with imported wool products but it is unclear how this species recently turned up in Norfolk as a pavement weed in North Walsham. Flowers July to August. A small, wiry-stemmed annual plant with tiny leaves that are typically on 1cm or so long. Flowerheads small, 3-7mm in diameter. A very easily overlooked plant which may prove to be present as an urban weed elsewhere in the region.
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Hairless Leptinella Cotula dioica
Introduced to the UK from New Zealand as a garden curiosity and recently found spreading onto roadsides from neighbouring properties in NE Norfolk. Flowers July to August. A creeping plant that forms lawn-like mats and spreads vegetatively, often without flowering. Leaves 2-3cm long, slightly succulent and distinctively covered in sunken glands. Despite the English name, the flower stems are quite hairy.
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Onehunga-weed Soliva sessilis
(Jo-Jo-weed, Bindi Weed, Lawn Burrweed). Introduced to the UK from South America, probably indirectly. First recorded in Hampshire in 1997 and first recorded in East Anglia in 2017. Currently known from East Suffolk and North Norfolk and, as elsewhere in the UK, appears to favour coastal campsites! Flowers July to August at least. A tiny, creeping plant that forms small tussocks, coming together to farm larger patches. Flowerheads just 4-10mm across, stalkless and with broadly ovate phyllaries surrounding the tiny florets. Flowereheads harbour small but sharp spines, rendering it painful to walk on in bare feet.
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