Yellow Thistles & Similar Species

Yellow Star-thistle Downy Safflower Common Safflower Giant Knapweed

What are they?

These plants are all thistle-like members of the Asteraceae, the huge family that includes all plants with a clustered 'moptop' of flowers above a basal section of greenish or brownish, scale-like bracts called phyllaries. Many of these plants have spines on the leaves and at the tips of the phyllaries for protection from grazing animals.

Where are they found?

None of the species on this page is native to the UK, so if found, they are most likely to be on waste ground, roadsides banks or in urban places.

Identification

This is a rather variable collection of plants, brought together by a similarity in their yellow or cream-coloured flowers. However, they are very diverse in the appearance of their leaves. As with most members of the Asteraceae, always remember to check the appearance of the phyllaries at the base of the compound flower head.



Common Safflower      Carthamus tinctorius

Introduced from southern Europe. Occasionally included in sown 'wildflower' mixes or sometimes appearing spontaneously from spilt bird seed, but never becoming established. Flowers July to September. The basal part of the flowerhead is swollen and covered in broad, leaf-like phyllaries with spiked tips. Leaves are broadly oval and the whole plant is more or less hairless. The petals become deep, orange-brown as they wither after flowering.

Common Safflower Common Safflower Common Safflower Common Safflower
Habit
Flowerhead
Leaf
Seedhead


Downy Safflower      Carthamus lanatus

Introduced from southern Europe. Occasionally included in sown 'wildflower' mixes or sometimes appearing spontaneously from spilt bird seed, but never becoming established. Flowers July to September. The basal part of the flowerhead is swollen and covered in narrow, spike-like phyllaries. Leaves are strongly toothed or lobed and the whole plant has downy, white hairs.

Downy Safflower Downy Safflower
Habit
Flowerhead


Yellow Star-thistle      Centaurea solstitialis

Introduced from southern Europe. Formerly recorded quite regularly as an arable weed amd more recently as growing from birdseed, but there has been no records since the 1970s. Flowers July to September. A very slender and upright plant covered with grey-white hairs and with strongly winged stems. Flowerheads have three-spined tips to the phyllaries.

Yellow Star-thistle Yellow Star-thistle Yellow Star-thistle Yellow Star-thistle
Habit
Flowerhead


Giant Knapweed      Centaurea macrocephala

Introduced from the Caucasus as a garden ornamental and recorded in the region on just a handful of occasions, although seeming not to persist in the wild for long. Flowers July to September. A tall, large-flowered species, regularly growing to a metre in height.

Giant Knapweed Giant Knapweed Giant Knapweed Giant Knapweed
Habit
Flowerhead
Phyllaries
Leaf


Cabbage Thistle      Cirsium oleraceum

Introduced. A rare casual, recorded less than 10 times as a short-lived garden escape or throw-out. Flowers July to September. Mostly a soft-leaved species with single small spines at the tips of the leaf lobes. Phyllaries hairless and upright, the outer few with a small spine at the tip. Flowers pale yellowish-white.

Cabbage Thistle Cabbage Thistle Cabbage Thistle
Habit
Flowerheads
Leaf