Cirsium, thistles |
The flower heads of thistles exclusively contain disc florets.
Cirsium rivulare, the brook thistle is common in southern Germany
In contrast to the genus Carduus the pappus is feathery
The morphological difference between the genera Cirsium and Carduus is relatively small: Cirsium species have fruits with feathery sailing hairs, whereas Carduus species have simple ones. The genus was described scientifically in 1754 by Philip Miller in his work Gardeners Dictionary.
Comprising at most 300 species, the genus is native to Eurasia, North Africa and North America and consists of annual, biannual or perennial herbaceous plants. The upright stem is sometimes spiny winged and slightly branched or simple. In Cirsium acaule the stems are often lacking. The basal leaves and the cauline leaves are thorny toothed and simple or one to three times pinnatipartite. The stem leaves are stalked to sessile and arranged alternate.
The flower heads are arranged solitary, clustered or in corymbose, spike-like or grape-like inflorescences. They contain only tubular flowers which are pink, purple, yellow or white. The floral tubes are 5-dentate, relatively long, slender, sometimes zygomorph and at the base without chaffy leaves. The florets are mostly hermaphrodite. Some species are dioecious. The flat or arched receptacle is densely covered with spines. The flower heads are surrounded by a tubular, ovoid or spherical involucre. The phyllaries are lance-shaped to ovate, upright, spreading or recurved, often mucronate and arranged imbricated in 5–20 rows.
After insect pollination (mostly by bees, bumblebees and butterflies) from the inferior ovary arises a slightly flattened, egg-shaped nut fruit (achene) with a lush and feathery pappus, consisting of 3–4 rows of flattened sailing hairs.
| Floral formula mostly: |
| * K=pappus [C(5) A5(connate)] G(2) inferior |
Historical publiations
Dioscorides und Pliny (1st century BC) wrote about "Kirsion" or "Cirsium" (possibly Carduus pycnocephala), it would be called great bugloss, because the stem leaves were similar to Anchusa but smaller and with soft spines at the margins. The purple flower heads would transform itself into a fringe of hair. Their roots would help against painful varicose veins.
Meaning of the species names
- arvense: lat. arvensis = of cultivated fields
- palustre: lat. paluster = of swampy grounds
- vulgare: lat. vulgaris = common
Interesting notes
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Cirsium oleraceum, the cabbage thistle can be used as wild a vegetable and is even cultivated in Japan.
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Cirsium arvense, the creeping thistle in agriculture is treated as a troublesome weed, which can spread quickly by means of stolons.