Pineapple weed (Matricaria discoidea) is an 18th century introduction from northeast Asia that escaped from Kew Gardens into the wild in 1871 to become the fastest spreading invasive plant species of the 20th century.
It is a sturdy annual that likes disturbed ground. Once out in the wild, though, it did not find this a conveniently empty habitat in which to establish itself: like all successful invasive aliens, it will have crowded native plants out of its niche.
Thoroughly naturalised now, it grows alongside the reserve’s footpaths, in the gateways and in cracks in the car park, places where passing footfall and traffic create even more difficulties for competitor species. A century and a half on, it’s hard to tell what might have grown in these places if it were not for this energetic escapee.
 Pineapple weed by H. Zell (CC BY-SA 3.0) via Wikimedia Commons  Pineapple weed © Mike Pennington (CC BY-SA 2.0) geograph.org
Header image: Ian Bushell
Pineapple weed belongs to the Asteraceae family and, like all asters, has composite flowers but unlike most composites, it does not have ray florets. In a common daisy the ray florets are the white petals around the edge of the flower but here (see image1) those marginal petals are undeveloped, the merest shreds of white between the yellow disc florets and the green bracts which surround the flower.
The internet is undecided as to the origin of the species’ common name. Some authorities say it is named for the pineapple-shape of its flower, others say that the feathery leaves smell and taste like pineapple.
It is one of those plants that we see everywhere but take no notice of; in our gardens we call it a weed and grub it out without a second thought. Next time you see it, pause long enough to look at its extraordinary flowers and to rub the scented leaves between your fingers.