Weeds - Identification of Injurious Weeds (PB4192)

CREEPING THISTLE
Cirsium arvense

Mature plant (Maggy Milner)

Young plant

Cirsium arvense

Creeping Thistle

A, a lower stem leaf; B, upper part of a female plant; C, flowering heads from male plant; D, upper part of male flower, partly cut away to show the stamens; E, upper part of female flower, partly cut away to show the stamens. Not to scale.

Young plant:

Seedling plants form small rosettes with a pair of opposite simple and unstalked oval cotyledon leaves. Paired light green true leaves are arranged at right angles to the cotyledons. These have wavy edges, weak spines and the upper surface supports hairs or weak bristles. Plantlets regenerating from root fragments more closely resemble the adult plant.

Adult plant:

The adult plant forms an extensive root system which can be exposed on digging. The flowering stems extend 30- 100cm or more in height from the shoots which emerge out of the rootstock each spring. These stems lack spines, wings, furrows or ridges.

The leaves are elongated and narrow with a wavy and strongly spined margin. The upper surfaces are quite glossy or waxy, whilst undersides are cottony or downy. There are separate male and female plants which can be distinguished by their different flower structures. Loose clusters of purple flower heads, each between 1.5 and 2.5cm long and around 1cm wide, are borne on the branched stems, from the end of June each year. The flowering stems die back after producing seeds.

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