Cirsium occidentale
Encyclopedia
Cirsium occidentale, with the common name Cobwebby thistle, is a species of thistle
native throughout California
deserts, mountains, and valleys, and in western Nevada, southern Oregon, and southwestern Idaho. Unlike many introduced exotic thistles, this native species is not a troublesome weed.
are winged and spiny and the leaves are toothed or edged with triangular lobes.
The inflorescence
at the top of the whitish stem holds one to several flower heads
. Each head is somewhat spherical, covered in large phyllaries
with very long, spreading spines which are laced, often quite heavily, in fibers resembling cobwebs
.
The head is packed with disc florets which may be white to blood red to shades of purple. The largest flower heads exceed 8 centimetres (3.1 in) in diameter.
Varieties
There are several varieties which differ from each other. For example Cirsium occidentale var. compactum the compact cobwebby thistle, is a short, clumpy plant which grows only along the coast of the San Francisco Bay Area
and Central Coast of California
region.
Thistle
Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles often occur all over the plant – on surfaces such as those of the stem and flat parts of leaves. These are an adaptation that protects the...
native throughout California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
deserts, mountains, and valleys, and in western Nevada, southern Oregon, and southwestern Idaho. Unlike many introduced exotic thistles, this native species is not a troublesome weed.
Description
Cirsium occidentale may be short or quite tall, forming low clumps or towering to heights approaching 3 metres (9.8 ft). The leaves are dull gray-green to bright white due to a coating of hairs, and the most basal ones on large plants may be nearly 0.5 metres (1.6 ft) in length. The petiolesPetiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
are winged and spiny and the leaves are toothed or edged with triangular lobes.
The inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
at the top of the whitish stem holds one to several flower heads
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
. Each head is somewhat spherical, covered in large phyllaries
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
with very long, spreading spines which are laced, often quite heavily, in fibers resembling cobwebs
Spider web
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....
.
The head is packed with disc florets which may be white to blood red to shades of purple. The largest flower heads exceed 8 centimetres (3.1 in) in diameter.
Varieties
There are several varieties which differ from each other. For example Cirsium occidentale var. compactum the compact cobwebby thistle, is a short, clumpy plant which grows only along the coast of the San Francisco Bay Area
San Francisco Bay Area
The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...
and Central Coast of California
Central Coast of California
The Central Coast is an area of California, United States, roughly spanning the area between the Monterey Bay and Point Conception. It extends through Santa Cruz County, San Benito County, Monterey County, San Luis Obispo County, and Santa Barbara County...
region.