Gamochaeta pensylvanica



Gamochaeta pensylvanica

(Willd.) Cabrera 1961

pronounced: gam-oh-KEE-tuh pen-sill-VAY-nick-uh

(Asteraceae — the daisy family)

synonym — Gnaphalium pensylvanicum

Willd. 1809

pronounced: naf-FAY-lee-um pen-sill-VAY-nick-um

common names: cudweed, Pennsylvanian cudweed

Gamochaeta is from the Greek γαμος (gamos), a marriage, and χαιτη (chaité), long flowing hair, referring to the united bristles in the pappus. In the synonym, Gnaphalium is from γναφαλλιον (gnaphallion), the ancient Greek name for a plant (Achillea maritima) whose soft whitish leaves were used for stuffing pillows. The specific is rather misleading, as the plant is not native to Pennsylvania*, and in fact is barely naturalized there, but probably comes originally from South America. It has been introduced into Eurasia, Africa, Australia and North America. In recent years it has been seen more often than before in southern Europe, and occasionally as far north as the Netherlands. It was recorded as a weed in a greenhouse near Liege as early as 1891, but not observed as an urban weed until 2007. It is thought to have spread as a small seedling in nursery pots.

There is some doubt as to the correct name of the plant. Most authorities give it as above, but Kew Gardens, in the latest version (1.1) of The Plant List, reverses my order of scientific name and synonym.

This is a plant of exposed moist soils, road verges, railway tracks and waste land throughout much of the world. In Australia, it is mostly found throughout the eastern half of Queensland, down the coastal strip of NSW, and, more rarely, in coastal areas of Victoria, South Australia and Western Australia. On Magnetic Island, I have seen it only in a sparse colony by a Picnic Bay roadside.

Cudweed is an annual herb, procumbent to erect, that grows to about 20 cm tall. It has a taproot. There is a basal rosette of leaves, and also cauline ones. Leaves are simple, oblanceolate to spatulate, up to about 7 cm in length, the apex rounded to obtuse, and mucronate, the base attenuate, the upper surface green and glabrescent, the lower surface white-tomentose to woolly. They are alternate, one leaf per node along the stem. The blades have no teeth or lobes, but the margins are sinuate.

The plant forms many small greenish flower heads in dense or loose terminal spikes subtended by 3 or 4 leafy bracts. The involucral bracts are oblong-elliptic to obovate, green to straw-coloured, the margins and tips hyaline, woolly at the base. The achenes are obovate, straw-coloured to light brown, microscopically papillate; the pappus bristles cohere at the base, as mentioned earlier, are minutely barbellate, but are not persistent. Each head contains 3 or 4 disk florets, but no ray florets. The flowerheads appear chaffy or papery, usually brownish.

Occasional plants appear that are intermediate between Gamochæta pensylvania and G. antillana. The latter differs in that it has more erect stems, linear to oblanceolate basal and proximal cauline leaves, and more nearly continuous arrays of heads with linear to narrowly oblanceolate bracts.


* Purists should note that I have not made a spelling mistake in the specific. Despite the fact that Pennsylvania has a double ‘n’, the specific does not.


Photographs taken in Picnic Bay 2013
Page last updated 2nd January 2019