T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Centaurea macrocephala (Giant knapweed)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Cynareae
Genus: Centaurea
Species: C. macrocephala
Binomial name: Centaurea macrocephala
Common names: Giant knapweed, Bighead knapweed, Yellow Hardhead, , Armenian basket flower, Pineapple Thistle, Lemon Fluff Knapweed, Globe centaurea, Yellow globe cornflower, Golden thistle

Centaurea macrocephala is a long-lived, herbaceous perennial that is native to Armenia, Turkey and the Caucasus Mountains. It is cultivated widely as an ornamental in temperate zone gardens. 

In New Zealand Centaurea macrocephala has the capability to become invasive and will become establish in natural areas where it will compete with native vegetation for nutrients and light. It will also out-compete grasses and other forage species, reducing food sources for wildlife and livestock. It reproduces by seed which can be spread by wind, passing animals, humans, vehicles or equipment. Many infestations that have occurred overseas are the result of garden escapees. A common practise is to use the flowers in dried arrangements, this facilitates seed dispersal. It is very difficult to remove once established.

Centaurea macrocephala is the largest Centaurea with several to many erect stems. The stems are un-branched or sparingly branched near the tips and grow 50-170 cm tall. The stems are covered with long soft hairs.
The leaves are broadly lance shaped, 10-38 cm long, and are slightly undulating with pointed tips and with margins that are smooth or shallowly dentate. The leaves which are rough to the touch are covered with short hairs and are dotted with resin glands.
The long lasting, bright yellow, thistle-like flowers are disc-shaped and can be up to 10 cm wide. The flowers are borne singly and composed of many yellow florets. The involucres (flower base) are 25-35 mm diameter and covered with 1-2 mm wide brown bracts having fringed edges, sometimes with weak spines. Flowers bloom mid-summer. The seeds are in-dehiscent, 7-8 mm long and with flattened bristles 5-8 mm long.

All parts of the plant are poisonous if ingested. Use caution when handling the plant as it has spines or sharp edges at certain times of the year and touching it may cause minor rashes. The pollen may cause allergic reactions such as hay fever.