Asteraceae-Thistle-Cirsium2017-08-16T14:24:24+00:00

Asteraceae: Sunflower Family – Cynareae (Thistle) Tribe: Cirsium

The Sunflower family is a very large family with over 25,000 members.  Botanists subdivide the family into a number of tribes of which 14 are represented in Monterey County, one of these, the Heliantheae or Sunflower tribe, being further broken down into subtribes of which 9 are represented in Monterey County. The Cynareae (Thistle tribe) has 8 genera present in California all of them alien and many invasive except for certain Cirsium which will be found on this page (along with one alien and invasive member of the genus).

Indian Thistle – Cirsium brevistylum

Blooms:

Mar–Aug

Plant Height:

3–35 dm

Flower Size:

Large

Origin:

Native

Habitat:

Moist, shaded or partly-shaded places

Notes:

The most characteristic feature of this thistle lies in the leaves which immediately subtend and sometimes surround the flower head.  This makes it easy to distinguish from the cobwebby thistles (sp. occidentale) which have long, leafless peduncles.

California / Bigelow Thistle – Cirsium occidentale var. californicum

Blooms:

Apr–July

Plant Height:

5–20 dm

Flower Size:

Large

Origin:

Native

Habitat:

Dry slopes

Notes:

The varieties of Cirsium occidentale all have more or less densely cobwebby heads and long, generally leafless peduncles.  Subtle differences in the form of the phyllaries (all spine-tipped in this genus), the color of the flowers and the degree of cobwebbiness separate the varieties.  This variety has a paler head — pink, lavender or white and the heads are more loosely clustered on long stems which are often totally naked for at least 15 cm below the heads. The phyllaries tend to be spreading or upward-curving like those of Cobwebby Thistle (var. occidentale) and range from glabrous to densely cobwebby, sometimes with a sticky resinous ridge.

Snowy Thistle – Cirsium occidentale var. candidissimum

Blooms:

Apr–Sept

Plant Height:

4–20 dm

Flower Size:

Large

Origin:

Native

Habitat:

Dry slopes, generally near coast

Notes:

The varieties of Cirsium occidentale all have more or less densely cobwebby heads and long, generally leafless peduncles.  Subtle differences in the form of the phyllaries (all spine-tipped in this genus), the color of the flowers and the degree of cobwebbiness separate the varieties.  The red to reddish-purple flowers of this variety are most similar to Venus Thistle (var. venustum) with spreading or down-curving phyllaries but the leaves, stem and heads are distinguished by their extraordinarily dense, white-tomentose cobwebbiness. Only the spiny tips of the phyllaries are without the cobwebbiness.

Cobwebby Thistle – Cirsium occidentale var. occidentale

Blooms:

Mar–July

Plant Height:

3–15 dm

Flower Size:

Large

Origin:

Native

Habitat:

Higher slopes, near coast and occasionally inland

Notes:

The varieties of Cirsium occidentale all have more or less densely cobwebby heads and long, generally leafless peduncles.  Subtle differences in the form of the phyllaries (all spine-tipped in this genus), the color of the flowers and the degree of cobwebbiness separate the varieties.  The red to purple-magenta (occasionally white) flowers of this variety are similar to those of Venus Thistle (var. venustum) but this variety is distinguished  by its phyllaries which are spreading or upward-curving. Stems are tomentose and leaves deeply lobed with undulating margins lined with prickles and spines.

Venus Thistle – Cirsium occidentale var. venustum

Blooms:

May–July

Plant Height:

5–30 dm

Flower Size:

Large

Origin:

Native

Habitat:

Mainly inland

Notes:

The varieties of Cirsium occidentale all have more or less densely cobwebby heads and long, generally leafless peduncles.  Subtle differences in the form of the phyllaries (all spine-tipped in this genus), the color of the flowers and the degree of cobwebbiness separate the varieties.  The red-pink to red flowers of this variety are most similar to Cobwebby Thistle (var. occidentale) except for the consistently redder color and the spreading or down-curving phyllaries.  Cobwebbiness is present but not  especially prominent in this variety.

Brownie Thistle – Cirsium quercetorum

Blooms:

Apr–Aug

Plant Height:

5–20 dm

Flower Size:

Large

Origin:

Native

Habitat:

Open places

Notes:

Unlike other members of this genus, this is a low-growing plant with a single flower head on a short peduncle.  Flowers may be white or purple and are surrounded by a rosette of distinctly spiny leaves.  Phyllaries are generally glabrous.  Pappus bristles are feathery and straw-colored to brownish, hence the plant’s common name.

Bull Thistle – Cirsium vulgare

Blooms:

May–Oct

Plant Height:

3–20 dm

Flower Size:

Large

Origin:

Europe

Invasive?

Yes – moderate

Habitat:

Disurbed places

Notes:

Unlike the other Cirsium species on this page, this is alien and invasive — and later blooming.  It has a large, round to vase-shape head and purple (occasionally white) flowers.  Leaves are large with long sharp spines at their tips and they extend up the stem to just below the flower head.