bull thistle (Cirsium vulgare)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

COMMON NAMES:
Scottish Thistle
bull thistle
common thistle
spear thistle

 

SCIENTIFIC SYNONYMS:
Ascalea lanceata Hill
Ascalea lanceolata (L.) Hill
Carduus divaricatus
Carduus firmus Steud.
Carduus lanceolatus L.
Carduus vulgaris Savi
Chamaepeuce firma DC.
Cirsium abyssinicum Sch. Bip. ex A. Rich.
Cirsium auriculatum Camus ex Beleze
Cirsium balearicum (Willk.) Porta
Cirsium balearicum Willk.
Cirsium britannicum Scop.
Cirsium dubium Lojac.
Cirsium firmum (C.Presl) Arcang.
Cirsium fraternum DC.
Cirsium lanceolatum (L.) Scop.
Cirsium lanigerum Nägeli
Cirsium leucanicum Lojac.
Cirsium linkii Nyman
Cirsium longespinosum Tod. ex Nyman
Cirsium microcephalum Lange
Cirsium mielichhoferi Saut.
Cirsium misilmerense Ces. & al.
Cirsium spurium Delastre
Cirsium strigosum (Hoffmanns. & Link) Cout.
Cnicus firmus J.Presl & C.Presl
Cnicus lanceolatus (L.) Willd.
Cnicus rectus hort.par. ex DC.
Cnicus strigosus Hoffmanns. & Link
Cynara lanceata Stokes
Eriolepis lanceolata (L.) Cass.

 

CONFIRMATION STATUS: Pending confirmation.

 

TAXONOMY: The currently accepted scientific name of bull thistle is
Cirsium vulgare (Savi) Ten. This is a very spiny thistle that can become
quite tall. It is easily distinguished from many of the native thistles by the
prickly bracts at the base of the flowerheads. These large bracts curl
outward and narrow into sharp points, while the bracts of native thistles
are appressed together and resemble green fish scales (fine spines are
usually present on the outer bracts for some native species). The leaf
undersides of the bull thistle are light green or whitish green, while the
leaf undersides for some native thistles, such as Cirsium discolor (pas-
ture thistle) and Cirsium altissimum (tall thistle), are powdery white in
appearance. Other native thistles, however, don't have this latter char-

acteristic. The bull thistle also has spines on its stems (from the decurrent

extensions of the leaves), while the stems of native thistles are spineless.

 

NATIVE STATUS: Introduced, United States and Canada.

 

GENERAL BOTANICAL CHARACTERISTICS:

 

Habit: This adventive plant is an obligatory biennial that forms a rosette

of leaves during the first year, and bolts upward during the second year to

produce flowers. It forms occasional side stems, but remains erect in stat-

ure, reaching 3-6' in height. The stout stems are light green, somewhat

angular, and covered with dense white hairs.

 

Leaves: The alternate leaves are up to 7" long and 2" across. In outline,
they are lanceolate in shape, but deeply pinnatifid. The widely spaced lobes
narrow into points that are individually armed with a pale yellow spine.
Some of the upper leaves near the flowerheads may be lanceolate or linear,
but remain unlobed. Across the surface of the leaves, there are short white
hairs and scattered small spines. The upper surface is dark green, while the
lower surface is light green. At the base of each leaf, there are a pair of
narrow wings that are dark green and decurrent against the stem. These
wings are extensions of the leaves and arm the stems with spines up to ¼"
long.

 

Flowers: The upper stems terminate in flowerheads of purplish pink to

purple flowers. Each flowerhead is 1½–2" across and contains numerous

disk florets, but no ray florets. Each disk floret is long and tubular, but

becomes divided into 5 long thread-like lobes. This provides the flower-

head with a showy hair-like appearance. At the base of each flowerhead,

are numerous green bracts that taper into stiff points that curl outward and

are quite prickly. Among these bracts are cobwebby hairs in the back-

ground.

 

Fruit/Seeds: They are replaced by achenes with large tufts of white hair.

These achenes are long, slender, and slightly ribbed. They are dispersed

by the wind.

 

Roots: The root system consists of a stout taproot that runs deep into the

ground. This plants spreads by reseeding itself and occasionally forms

colonies.

 

REGENERATION PROCESS: Seedlings appear from autumn to April
and they do not begin to flower until their second year of growth. Flowers
are produced from July to September, and are pollinated by long-tongued
bees, hover-flies and butterflies. Individual plants can produce a great
abundance of seed, which have a high germination and survival rate (After
the seeds have been produced, the flowering stems die back). Thus, this
plant can be quite aggressive. Because the seeds remain viable for only
1-2 years, one control strategy consists of destroying individual plants
before they reach the flowering stage. It is possible for a plant to reestab-
lish itself if a portion of the taproot remains in the ground.

 

HABITAT TYPES: It is adventive from Eurasia, and has existed in
the United States since the 19th century, if not earlier. Habitats include
pastures, abandoned fields, fence rows, areas along roadsides and rail-

roads, cut-over woods, and miscellaneous waste areas. This species
prefers disturbed areas and is not common in high quality natural habi-

tats. This thistle usually grows in full sun under moist to dry conditions.

It prefers a fertile soil that consists of loam, clay loam, or that is slightly
stony. Occasionally the foliage is affected by mildew during the summer
or fall. Individual plants can produce a great abundance of seed, which
have a high germination and survival rate. Thus, this plant can be quite
aggressive. Because the seeds remain viable for only 1-2 years, one con-

trol strategy consists of destroying individual plants before they reach
the flowering stage. It is possible for a plant to reestablish itself if a por-

tion of the taproot remains in the ground.

 

SITE CHARACTERISTICS: Bull thistle usually grows in full sun under

moist to dry conditions. It prefers a fertile soil that consists of loam, clay

loam, or that is slightly stony. Occasionally the foliage is affected by mil-

dew during the summer or fall.

 

SEASONAL DEVELOPMENT: The blooming period occurs from mid-

to late summer (July to September) and lasts about 3-4 weeks, after which
the florets wither away.

 

GENERAL DISTRIBUTION: An invasive from Eruasia, bull thistle is

found in every state in the United States and has been reported in most

Canadian provinces.

 

SKY MEADOWS DISTRIBUTION: To be determined.

 

IMPORTANCE AND USES: The nectar and pollen of the flowers attract
many kinds of long-tongued bees, including bumblebees, large leaf-cutting
bees, miner bees, and epeoline cuckoo bees. The flower nectar also attracts
butterflies (especially swallowtails), skippers, and bee flies. Green metallic
bees and other halictid bees may collect pollen from the flowers, but they
are non-pollinating. The caterpillars of the butterfly Vanessa cardui (paint-

ed lady) feed on the foliage. There are also many moth species with cater-

pillars that consume various parts of thistles. The seeds are eaten by gold-

finches and the clay-colored sparrow. Goldfinches also use the tufts of
hair as construction material for their little nests. Mammalian herbivores
don't eat the bull thistle because it is heavily armed with spines. Even in
overgrazed pastures where cattle and sheep have little to eat, the bull thistle
is one of the few plants that is left alone. It can increase in heavily grazed
pastures.

 

 

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