Key characteristics

The large variety of thistles present in New Zealand include

Almost all of these are weeds of pasture. Below are their key characteristics.

Nodding thistle (Carduus nutans)

• Flower heads are nodding (droopy), usually red-purple, globose. Those on the main stem are usually 2 – 6 cm across but are smaller on side stems. They are solitary, and the stalks just below the flower head are bare
• Leaf margins are spiny, as are the ‘wings’ on the stems
• Leaves are dark green, deeply divided into triangular lobes with spiny tips, and do not have large, distinct white markings, although the leaf margins are white at the base of the marginal spines
• Flower stalks arise from rosette of leaves in either the first or second year
• Seeds have thistle down which helps in seed dispersal.

Californian thistle (Cirsium arvense)

• Perennial thistle with underground creeping roots from which many shoots emerge
• Slender flower stems up to 1 m tall with a cluster of flowers at the top, usually occurring in small or large patches
• Flowers December to February with purple or mauve (very rarely white) flower heads, each 1.5 to 2.5 cm long
• Leaves hairless on the upper side and paler underneath, with shallow notches between triangular, spiny lobes
• Male and female flowers on separate plants; the male flower head is always shorter and less urn-shaped than the female flower head
• Patches of Californian thistles are often a single plant, the flower stems all rising from the same roots. The whole patch often has flowers of the same colour and these are either male or female.

Scotch thistle (Cirsium vulgare)

• Erect, branched flowering stems can be up to 1.5 m tall and arise from a large rosette of leaves fairly flat to the ground. The rosette has a large taproot
• Flowers from November to March producing large reddish-purple flower heads which grow solitary or in clusters of two or three heads
• Outer bracts of the flower heads are slightly hairy with strong, sharp spines up to 4 mm long
• Leaves are large (up to 30 cm x 10 cm), dark green, with prickly hairs on the upper surface and white cottony hair on the lower surface
• Flowering plants can appear very bushy late in the summer and in autumn
• Seeds each have a feathery pappus (thistledown), which may assist dispersal by wind
• Very common in New Zealand’s pastures, wastelands, forests and roadsides.

Plumeless thistle (Carduus acanthoides)

• Very similar in appearance to nodding thistle, particularly in the rosette stage
• Flower heads are purple, small and erect (don’t droop or ‘nod’), and do not have backwards curving bracts
• Very common in the Waikato but also found in similar habitats to nodding thistle across   the North Island and occasionally in Canterbury.

Cotton thistle (Onopordum acanthium)

• Biennial thistle with a taproot, growing up to 1.5 m tall with large, erect, red-purple single flower heads, which can be solitary or in clusters
• Leaves are similar to Scotch thistle, but larger and a blue-grey colour. They are covered with a mat of woolly hairs, especially on the lower surface of the leaves
• Flowers December to February then produces seeds about 5 mm long covered in a rough to touch pappus
• Stems are broadly-winged and covered in white cottony hairs
• Usually found only in South Island, mostly along roadsides.

Marsh thistle (Cirsium palustre)

• Biennial thistle growing up to 1.5 m tall, with a fibrous root system
• Individual flowerheads are small (about 1 cm diameter) and grow in clusters of up to ten on one short stalk
• Leaves are similar to Scotch thistle, but narrower and more finely divided
• Flowers November to February before producing seeds with a feathery pappus
• Stems are branched towards the top with fine cobweb-like hairs and spiny wings
• Common in damp areas of pasture and wasteland, also common in high rainfall areas of the North Island and occasionally found in the South Island.

Saffron thistle (Carthamus lanatus)

• Annual thistle that starts out as a taprooted rosette which in spring produces stems up to 50 cm tall. These are branched and hairy, but not winged, and have solitary flower heads each about 2 cm in diameter
• Flowers have saffron-yellow petals and relatively soft (not prickly) leaves, but there are vicious spines around the flowerheads
• Leaves are dark green and glossy with sharp tipped (but not prickly) lobes that are cut half way to the midrib. Leaves are stalkless, narrowly triangular in shape and up to cm long by 3 cm wide
• Flowers January to April, followed by seed heads. Seeds are quite large and do not have an obvious pappus (thistledown)
• Native to Europe, this thistle is now found in New Zealand pastures, wastelands, roadsides and railways. Seeds are a common component of birdseed and as a result the thistle is often found round chicken coops.

Winged thistle (Carduus tenuiflorus)

• Annual plants start life as a tap-rooted rosette
• Tall (to 1 m) erect, spiny, branched, winged stems bearing at the top dense clusters of three to eight stalkless, smallish (up to 1.5 cm wide) flower heads
• Most seeds germinate in autumn, and the plant produces flowering stems in spring
• Flowers appear between November and December, followed by seed heads with small brown seeds each with a simple pappus 10 – 12 mm long
• Leaves are spiny, deeply lobed and up to 30 cm long by 15 cm wide. Upper surface is green and underside cottony
• Plants are often found in very dense patches
• Common throughout both the North and South Islands, this thistle invades pastures, roadsides and wastelands, especially in places where pasture cover was poor or damaged the previous autumn.

Slender winged thistle (Carduus pycnocephalus)

• Very similar to winged thistle in all aspects, although flowerheads are in smaller clusters of only two or three, and are on short stalks and the involucralbracts around the flowerhead have a raised midrib in the upper half as opposed to just the upper thirds in winged thistles
• Flower heads are cylindrical, about 1 cm across in clusters of one to three, and the flowers are red, purple or mauve and fall when mature
• Stem wings are narrower between the clusters of teeth
• Very similar in appearance to winged thistle but usually appears to be more slender. Individual plants can be hard to classify as one species or the other
• Often occurs in patches along with winged thistle, and its distribution is similar.

Star thistle (Centaurea calcitrapa)

• Biennial thistle that starts life as a taprooted rosette, and produces, between November and March, an erect, branched and hairy flower stem up to 60 cm tall
• Leaves are divided into many lobes and have bristles but are not prickly
• Produces pink-purple flowerheads between November and April, the flowers being about 8 mm in diameter with vicious yellow spines around the heads
• Common in parts of the North and South Islands in pastures, waste places and roadsides.

Variegated thistle (Silybum marianum)

• Most characteristic feature is the very large and very spiny seed head, although the large-leafed rosettes, with white veins on the upper surface of the leaf are also distinctive
• Flower heads are large, with reddish purple petals, and are surrounded by very sharp, long spines
• Seeds germinate mostly in the autumn but can also germinate at other times of the year. After germination very large leafy rosettes are formed. In November or December these rosettes produce very large (up to 2 m tall) flower stems that, in December to March, produce the large flowerheads
• Flower stems are branched towards the top, but do not have wings running up them
• Lobes of the leaves are tipped with long, sharp spines
• Plants often occur in large, dense colonies
• Leaves can be toxic to livestock
• This thistle used to be much more common before the introduction of the first phenoxy herbicides, to which it is very sensitive.