MMM #16: Super Sweet, Proper Prickly Invader!
This is the 16th of a 17-cache series which will take you on a wonderful 6km looping trail up the deep Morton valley through Sunnydale and The Glen passing historical farm and residential buildings, industrial ruins, mill ponds and weirs, rich deciduous and pine woodlands, a reservoir, waterfall, low moorland, farm fields and then back down an old track and flower-festooned path into the village.
The cache, a camo-lidded 35mm film pot, is hidden further down Upwood Lane at a location where an unusual 4-gate arrangement forms an enclosed area - maybe for manipulating sheep movements?
Continuing with the common plants theme, another unmistakable - and very prickly - one you will have seen abundantly during your walk is the thistle - but which one?
Of the at least 17 (!) species (of which 10 are indigenous) occurring in Britain, the most common is the Creeping Thistle Cirsium arvense of which there are numerous varieties with slightly different features. The species name arvense is from Latin meaning 'of the field'.
It is a perennial member of the daisy family Asteraceae, native throughout Europe and western Asia, northern Africa and widely introduced elsewhere. It is also commonly known as Canada thistle, field thistle, lettuce from hell thistle, California thistle, corn thistle, cursed thistle, field thistle, green thistle, hard thistle, perennial thistle, prickly thistle, setose thistle, small-flowered thistle, way thistle, and stinger-needles. It grows in disturbed and grassy places.
It is good for pollinators that rely on nectar and is also was a top producer of nectar sugar in a 2016 study in Britain, with a 2nd place ranking for 'weeds' after Common Ragwort aka Stinking Willy (Senecio jacobaea).
It is a C3 carbon fixation plant. These originated during Mesozoic and Paleozoic eras, and tend to thrive in areas where sunlight intensity and temperatures are moderate, and ground water plentiful. They lose 97% of the water taken up through their roots to transpiration.
Creeping thistle is a herbaceous perennial plant growing up to 150 cm, forming extensive clonal colonies
from thickened roots that send up numerous erect shoots during the growing season (ie. clonal propagation). It is a ruderal species ie. growing on waste ground - as well as roadside verges, woodland edges, wasteland and field margins. It is a common weed of cultivation and many permanent pastures. Given its highly adaptive and fast-spreading nature, it is one of the world's worst invasive weeds with seriously detrimental effects on crop production.
Its complex underground network and consists of 4 types: 1) long, thick, horizontal roots, 2) long, thick, vertical roots which can reach up to 4m long (giving it great drought tolerance), 3) short, fine shoots, and 4) vertical, underground stems. As incorrectly stated in some sources it does not form rhizomes. Root buds form adventitiously on the thickened roots of creeping thistle, and give rise to new shoots. Shoots can also arise from the lateral buds on the underground portion of regular shoots, particularly if the shoots are cut off through mowing or when stem segments are buried.
Every plant species has a unique floral fragrance and its fragrance - which increases with age - contains compounds which attract both pollinators and florivores. Non-native honeybees are shown to have the highest visitation rate, following other bee species in the genera Halictus and Lasioglossum. Hover flies are also commonly seen pollinating the flower heads of this plant. Florivores like beetles and grasshoppers are commonly seen as well. The fragrance contains several compounds that attract diverse insects.
1-5 pinky-lilac flower heads (June to August) occur per branch, with plants in very favourable conditions producing up to 100 heads per shoot. Each head has about 100 florets. Average seed production per plant is about 1530 but this can vary from 1,000 to 40,000 depending on the number of flower stems and inflorescences.
More seeds are produced when male and female plants are closer together, as flowers are primarily insect-pollinated. It can bloom from seed in a year then subsequently the seeds produced can emerge in the following year.
The seeds are an important food for the goldfinch (aka thistle finch) and the linnet, and to a lesser extent for other finches. The seed down is used to line the nests of various birds.
Its foliage is used as a food by over 20 species of Lepidoptera, including the painted lady butterfly and the
engrailed moth, and several species of aphids. The flowers are visited by a wide variety of insects such as bees, moths, wasps and beetles (the generalised pollination syndrome).
It is widely considered a weed even where it is native, eg. in UK it is designated an 'injurious weed*' under the Weeds Act 1959 - one of only 5 species listed. See here for a detailed illustrated Government leaflet on Identification of Injurious Weeds. It is also a serious invasive species in many places where it has been introduced, usually accidentally as a contaminant in cereal crop seeds.
* a native species deemed to damage farming productivity
Uses: like other Cirsium species its roots are edible, but rarely used, not least because they may cause flatulence in some people. The taproot is considered the most nutritious part. The leaves are also edible, though the spines make their preparation for food too tedious to be worthwhile. The stalks, however, are also edible and more easily despined. Some gin distilleries use it as one of the many botanical forages used to flavour the gin. The feathery pappus is also used by the Cherokee to fletch blowgun darts.