Al Schneider's Rocky Mountains Plant Descriptions

Creeping Thistle
Cirsium arvense
Aster family (Asteraceae)

An invasive plant introduced to North America from Eurasia, Creeping Thistle (once called Canada Thistle) is often found in large patches having spread by deep . The plant is a favorite food of the Painted Lady butterfly caterpillar. The Bull Thistle (C. vulgare) and Musk, or Nodding Thistle (Carduus nutans) are two other introduced thistles. They have spiny-winged stems, cut leaves with bristly hairs, and larger, showier flowerheads than those of Creeping Thistle.

In 1753 Linnaeus named this species, a native of Eurasia, "Serratula arvensis," and it was renamed "Cirsium arvense" in 1772. "Arvense" is Latin for "of fields." "Cirsium," is Greek for "dilated vein" from the bygone belief that a thistle distillate opens clogged veins. We now know that only Draino does that.


©2010 Matt Lavin

Description

Non-native , 2-5' tall, that forms colonies from its root system. Leaves are sharply or and waxy with spiny tips, , usually stalkless, and commonly white-woolly on the undersides. Cylindrical pink-purple flowerheads arise from branches. Flowers are numerous on open, spineless stalks. Flowerheads are comprised of flowers only. Unlike other thistles the male and female flowers appear on separate plants. , , are borne on numerous, feathery white-brown hairs.

Field Marks

Pink flowerheads and irregular leaves with on margins only.

© Al Schneider

lobe -- Being divided by clefts.

achene -- a type of simple dry fruit produced by many species of flowering plants. For example, a rose hip holds a few achenes.

A herb is a plant whose stems die back to the ground in the winter.

ribbed -- having prominent, narrow parallel protrusions that extend over most of its length or circumference.

pappus -- Small scales, bristles or hairs at the top of the seed in Asteraceae. For example, dandelion parachutes. Plural: pappi.

terminal -- Located at the end (the tip or the apex).

spine -- a stiff, sharp structure formed by the modification of a plant organ that contains vascular tissue. A spine can be formed by a latteral branch, a modified leaf or a thorn.

Like the teeth on a saw, leaves and other surfaces can have toothed edges.

fruit -- any seed-bearing structure in flowering plants. It is formed from the ovary after flowering.

pinnate -- A compound leaf with two rows of leaflets.

disc flowers are those in the center of a sunflower or daisy. Not a ray flower.

rhizome -- root-like stems that may either grow horizontally at the soil surface or in other orientations underground.

alternate -- leaves alternate along the main stem and are attached singly.

A perennial plant lives and blooms for many years.