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North dakota State University
NDSU Extension Service
The Thistles of North Dakota
W-1120, October 1996
Rodney G. Lym, Professor, Department of Plant Sciences
Katheryn M. Christianson, Research Specialist, Department
of Plant Sciences
Thistle is an old English name,
essentially the same in all languages, for a large group of
plants with a dubious reputation. In ancient history the thistle
represented part of the primeval curse on the earth in general,
and on man in particular. In Greek history Earth made the thistle
in a moment of grief for the loss of Daphnis, shepherd and
musician, poet and hunter. In Norse mythology Thor, the
thunderer, protected the plant, known as the lightning plant, and
all those that wore it from harm. The common cotton thistle or
Scotch thistle (Onopordum acanthium L.) has regal stature.
During the reign of Malcolm I of Scotland, Norsemen attempted to
capture the Staines Castle by wading across the moat in their
bare feet, only to find the moat dry and overgrown with thistle.
The painful cries of the warriors roused the castle guards and
the Norsemen were defeated. To commemorate this victory, the
flower became the emblem of Scotland. In some translations,
thistle is also the basis of Hans Christian Anderson's tale The
Wild Swans, where eleven princes were freed from their
entrapment as swans when their sister made shirts from thistle
and placed them on their backs.
Thistles in agriculture have a reputation as a sign of
untidiness and neglect, and are often found on good ground not
properly cared for. However, this unfortunate characteristic is
only true of a few invasive species and is not accurate for the
vast majority of native thistles which have many useful traits.
Europeans, Native Americans, and early settlers found many
thistle species edible as well as useful for medicinal purposes.
Thistle achenes as raw seeds are bitter but were often roasted
before being eaten. The young leaves of Canada, bull, and
plumeless thistle, with the spines removed, can be served as a
salad or cooked like spinach. The inner stem pith can be steamed
and served like asparagus, once the outer layer is peeled off.
The heads of these plants also can be used as a rennet to curdle
milk for cheese making.
Blessed thistle (Cnicus benedictus L.) is cultivated in
southern Europe and has the reputation of curing many ills,
including the plague. Extracts from milk thistle [Silybum
marianum (L.) Gaertn.] are sold in health food stores to
combat the liver diseases, hepatitis and cirrhosis. The extracts
contain silymarin, a compound that may inhibit toxins from
translocating across liver cell membranes. Thistle plumes,
especially musk thistle pappus, were used to make paper during
the 18th century.
Many native birds and insects utilize the various thistle
species as a food source and for materials to build nests.
Goldfinches feed on several thistle species, and bees utilize the
plants to make an especially sweet honey. Many butterfly larvae,
especially in the metalmark group, use thistle as their main or
only food source. Wasps, flies, and beetles feed on the pollen of
thistle flowers, which in turn provide a food source for other
wildlife.
Nine species of thistle are found in North Dakota, of which
five are native and one is considered rare. North Dakota has a
relatively low population of native thistles compared to most
western states, which commonly have 25 or more native thistle
species. Some plants referred to as thistles such as perennial
sowthistle (Sonchus arvensis L.) and Russian thistle (Salsola
iberica Sennen) are not true thistles, but rather are plants
with poorly chosen common names. Most native thistle species go
unnoticed. Only a few introduced thistles have become weedy
pests. There are approximately 160 native thistle species in
North America, with at least 110 species north of Mexico and 50
in Latin America south of the Mexican border.
Native North Dakota
Thistles
Of the five native thistle species in North Dakota, Flodman
and wavyleaf thistle are perennials, while tall, field, and swamp
thistle are biennials. Flodman thistle is the most common of
these plants and is found in all North Dakota counties, while
tall thistle is considered rare and is on the
threatened/endangered species list in some regions.
Figure 1. Distribution
of native thistles in North Dakota by county. A highlighted
county indicates one or more documented occurrences, although
the species may be found elsewhere.
Flodman Thistle, Cirsium
flodmanii (3KB color map)
Field Thistle, Cirsium
discolor (3KB color map)
Wavyleaf Thistle,
Cirsium undulatum (3KB
color map)
Swamp Thistle, Cirsium
muticum (3KB color map)
Tall Thistle, Cirsium
altissimum (3KB color map)
Flodman thistle [Cirsium
flodmanii (Rydb.) Arthur]
Flodman thistle is more competitive than most other native
species, has the potential to infest large areas, and is found
throughout North Dakota (Figure 1 - 3KB color map). Flodman thistle is a deep-rooted
perennial (sometimes biennial) and grows 2 to 3 feet tall (Figure
2). The leaves are shiny green on top with slight pubescence and
are white and very pubescent below (Figure 3), alternate, rigid
and deeply lobed, and end in a spine. Each lobe has three points,
one of which sticks out at near right-angles giving them a
"flipping appearance", which is a helpful way to tell
this plant from the often similar appearing wavyleaf thistle
(Figure 4). The rosettes are often 4 to 6 inches in diameter with
oblong or lanceolate leaves which vary from very lobed to only
remotely lobed (Figure 5). The leaves are green to gray and
especially pubescent below.
Figure 2. Flodman
thistle flowering plant showing deeply toothed alternate
leaves and gray stem. (28KB color photo)
Figure 3. Underside of
Flodman thistle leaves which are gray and highly pubescent. (39KB color photo)
Figure 4. The nearly
upright or "flipping" lobes of Flodman thistle and
the shiny green upper-surface of the leaves, help distinguish
it from wavyleaf thistle. (30KB color
photo)
Figure 5. Flodman
thistle rosette with lance shaped leaves. (41KB
color photo)
The flowers are deep purple to pink, tube shaped and
approximately 1 inch long (Figure 6). The flower heads (involucre
bracts) have a strong yellow spine and a sticky secretion which
attracts and catches insects. Flodman thistle usually flowers
from mid-July through September. A white flowering form
occasionally is found in North Dakota (Figure 7). The achenes are
about 0.1 to 0.15 inches long, oval, vary from tan to brown and
have a conspicuous yellow collar (Figure
25a - 18KB color photo).
Figure 6. Flodman
thistle flower with strong yellow spine on the tube shaped
head. A sticky secretion attracts and catches insects. (31KB color photo)
Figure 7. A white
flowering form of Flodman thistle can be found in small
patches surrounded by the much more common purple flowering
form. (52KB color photo)
Flodman thistle is tolerant to high salt concentration in soil
but grows best under moist conditions, as most thistles do.
Flodman thistle can survive under drought conditions which gives
it a competitive advantage on semi-arid rangeland. The stems of
Flodman thistle can be peeled and eaten and were part of the
Native American diet.
Wavyleaf thistle [Cirsium
undulatum (Nutt.) Spreng.]
Wavyleaf thistle is often confused with Flodman thistle but is
a larger plant and generally is found in drier locations than
those occupied by Flodman thistle. Both species are perennials in
North Dakota. Generally, Flodman thistle is more common than
wavyleaf in eastern North Dakota, but wavyleaf gradually becomes
the predominate species in central and western portions of the
state (Figure 1 - 3KB
color map). Wavy-leaf thistle flowers from July to
September, which is a week or two earlier than Flodman thistle.
Wavyleaf thistle tends to be more spiny than Flodman thistle and
often grows to 4 feet in height (Figure 8).
Figure 8. Flowering
wavyleaf thistle plant which is very pubescent and gray in
color with leaves much less divided than Flodman thistle. (72KB color photo)
The leaves of wavyleaf thistle are alternate and tipped with
yellow spines. This thistle is sometimes called gray thistle
because it has a white cast. The surfaces are very pubescent and
the margins are strongly undulated or wavy (Figure 9). The leaves
are less deeply lobed than Flodman thistle. The stem of wavyleaf
thistle is very pubescent and generally thicker than Flodman
thistle (Figure 10). Rosette leaves also are very wavy and gray
in appearance (Figure 11), unlike Flodman thistle. The underside
of the rosette is especially pubescent.
Figure 9. Wavyleaf
thistle leaves are tipped with a yellow spine, similar to
Flodman thistle. However, the leaves of wavyleaf thistle are
very pubescent both above and below and undulated without the
"flipping" appearance of Flodman. (46KB color photo)
Figure 10. Stems of
wavyleaf thistle are very pubescent and thicker than Flodman
thistle. (30KB color photo)
Figure 11. Rosette of
wavyleaf thistle, which is also called gray thistle because
of the dense pubescence. (34KB color
photo)
The flowers of wavyleaf thistle are larger than Flodman,
usually more than 2 inches long (Figure 12). The large
globe-shaped heads contain glands that are tipped with strong
yellow spines. The flowers are most often pink or purple, but
there is a white flowered form, f. album Farwell. The
achenes are brown without a lighter apical band or with only a
very narrow lighter margin (Figure 25b
- 17KB color photo).
Figure 12. Large
globe-shaped head of wavyleaf thistle which can vary in color
from pink to wine-red. (25KB color photo)
Various Native American tribes used wavyleaf thistle to treat
gonorrhea and syphilis. The remedy involved drinking a tea made
from the plant and then elevating the body temperature to induce
sweating. If the patient were male, he had to run a mile then,
wrap himself in a blanket. A female patient just sat bundled in a
heavy blanket to induce sweating. Others have reported that a tea
from the roots can be made to treat diabetes and stomachache. The
roots were also boiled and used in soup.
Field thistle [Cirsium
discolor (Muhl. ex Willd.) Spreng.]
Field thistle has only been documented to occur in extreme
eastern North Dakota (Figure 1 - 3KB color map), although it is quite common in
Minnesota and most of eastern North America. Field thistle is
found by roadsides, in clearings and openings in wooded areas,
and in moist but not marshy locations. It generally grows 6 to 7
feet tall in North Dakota, but can reach heights up to 10 feet.
The tall plant and leaves that resemble oak leaves are two good
characteristics for identification of this plant in North Dakota
(Figure 13).
Figure 13. Field
thistle grows 6 to 7 feet tall in North Dakota and is usually
found on the edge of woods in the eastern part of the state.
Each stem has a single head. (52KB color
photo)
The stems of field thistle are woody, hollow, ribbed and green
to green-brown with little pubescence. The plant has many
branches, and each branch has a single flower head. The lower
leaves are large (10 by 20 inches) and deeply lobed, resembling
an oak leaf (Figure 14). The leaves are light green and shiny on
top, pubescent underneath, with very small unimpressive spines.
The leaves get progressively smaller toward the top of the plant.
The rosette leaves are similar in shape to stem leaves but grow
up to 12 inches long (Figure 15).
Figure 14. Leaves of
field thistle grow 10 to 20 inches long, have few spines, and
resemble an oak leaf. (28KB color photo)
Figure 15. The
initial leaves of a field thistle rosette are very large but
otherwise indistinguishable from other thistles until the
characteristic oak-leaf shape is exhibited. (23KB color photo)
The flowers are pink to lavender, rarely white in color, and
the heads are 1.5 to 2 inches wide by 1.5 inches in height
(Figures 16 and 17). Each flower head has about eight rows of
progressively longer bracts, the outer five rows of which have
0.25 inch long spines bent out and down. There are numerous
leaflike bracts around each flower head. The plant begins
flowering in late July through September. Achenes are 0.2 inches
long, light brown with darker stripes and a yellow apical collar
(Figure 25c - 19KB color
photo).
Figure 16. The common
pink head of field thistle has many short spines and is
surrounded by small very divided leaves which give the plant
an elegant appearance. (32KB color photo)
Figure 17. The white
flowering form of field thistle. (16KB
color photo)
Field thistle is closely related to tall thistle. North Dakota
is on the border of the ranges of both species. While they have
been found in the state, they are considered uncommon.
Swamp thistle (Cirsium
muticum Michx.)
As its name implies, swamp thistle is found in moist low-lying
woodland areas, thickets, and near rivers and especially wet
meadows. It is found in eastern North Dakota and in the Bottineau
area (Figure 1 - 3KB
color map). Swamp thistle is an elegant long-stemmed
flowering plant that usually grows 3 to 6 feet tall (Figure 18).
Swamp thistle has very few and weak spines on the leaf margins
and no spines around the flower head, which is an easy way to
tell it apart from field thistle and tall thistle.
Figure 18. Swamp
thistle grows in and near wooded areas and is difficult to
spot even when it flowers in mid-July. (22KB
color photo)
Swamp thistle is a biennial with a soft, hollow, and ribbed
stem green in color with fine hairs. The leaves are light green,
oblong with deep lobes to lanceolate, and the lobes usually are
tipped with a small weak spine and almost hairless (Figure 19).
The leaves are up to 10 inches long and 4 inches wide at the base
but become progressively smaller and more lanceolate towards the
tip (Figure 20). The rosette leaves are generally oblong and can
grow to 22 inches long and 8 inches wide.
Figure 19. The leaves
of swamp thistle are nearly hairless and tipped with weak
spines. (16KB color photo)
Figure 20. Swamp
thistle stems are hollow and ribbed, leaves are sparse, and
heads can be found solitary or in clusters. (19KB color photo)
Swamp thistle flowers somewhat earlier than field thistle,
mid-July through early September. The heads are about 1.5 inches
across and bell shaped, and the bracts are sticky and gray to
white resembling cobwebs (Figure 21). The flowers are dark purple
to lavender, generally the color of red wine (rarely white) and
can be solitary or in clusters. The achenes are about 0.25 inches
long, narrow, and dark brown to black in color with a yellow
apical band (Figure 25d - 19KB color photo). The swamp metalmark butterfly
will lay eggs only on swamp thistle which is the caterpillar's
only food source.
Figure 21. A rapid
way to distinguish swamp thistle from field and tall thistle
is to squeeze the flower heads, which are spineless, while
the other species will leave a "sharp" impression.
Also, the swamp thistle involucre bracts resemble cobwebs. (25KB color photo)
Tall thistle [Cirsium
altissimum (L.) Spreng]
Tall thistle is closely related to field thistle and can be
difficult to distinguish. Tall thistle is found in Nebraska where
field thistle does not occur, and only field thistle, not tall
thistle, is found in Canada. Although both species have been
found in North Dakota (Figure 1 - 3KB color map), they are considered uncommon and
the characteristics that are used to distinguish these two
species blur in the northern Great Plains.
Tall thistle is a biennial that grows from 3 to 8 feet tall.
The stems are light green and freely branched (Figure 22). Most
leaves are lanceolate or long-ovate, tapered at the end and not
as deeply lobed as field thistle leaves. The leaves of tall
thistle more closely resemble dandelion leaves, compared to the
oak-leaf shape of field thistle (Figure 23). The leaves are green
on top, densely pubescent and white beneath, and 4 to 11 inches
long and 1.5 to 4 inches wide. Leaves near the base are largest
and gradually are smaller and more elliptical toward the top. The
leaves are alternate and toothed or with weak spines. Rosette
leaves are similar to the lower leaves of the bolted plant, large
and only slightly lobed.
Figure 22. Tall
thistle flowering plant with leaves resembling a dandelion,
light green freely branched stems, and solitary flowers at
the end of each branch. (35KB color photo)
Figure 23. Leaves of
tall thistle can be oval shaped or toothed, are pubescent
underneath, and shiny green on top with weak spines. (23KB color photo)
The heads are 1.5 to 2 inches long and 2 inches wide, mostly
solitary at the end of branches (Figure 24). The leaves
surrounding the heads are oblong and not divided as they are in
field thistle and have shorter spines. The flowers generally are
light purple but can be dark purple, rarely white, and flowering
occurs beginning in July to early September. The achenes are pale
to dark brown with a yellow apical ring with incomplete stripes,
0.15 to 0.25 inches long and 0.1 inch wide (Figure
25e - 18KB color photo). Wild turkeys
often feed on tall thistle seed in the fall.
Figure 24. Tall
thistle flowers have one or more long undivided leaves just
below the head. (29KB color photo)
Tall thistle is commonly found near woods, in open lowlands,
and near ditches and roads. It occasionally occurs on the slopes
of open prairies. Tall thistle has only been reported in eastern
North Dakota.
Figure 25. North Dakota
thistle achenes, commonly called seeds:
Invasive North
Dakota Thistles
Thistle species introduced from Europe and Eurasia often
spread rapidly and become weedy because the natural enemies that
keep the populations in check in their native habitat are not
found in North America. At least 19 thistle species have been
declared noxious according to state weed control laws or seed
laws in the United States. The most common noxious thistle
species include Canada, musk, bull, plumeless, and Scotch
thistles. All except Scotch thistle are found in North Dakota.
Consult North Dakota State University Extension Service Circular
W-799, Perennial and Biennial Thistle Control, for weed
control guidelines.
Figure 26. Distribution
of introduced thistles in North Dakota by county. A
highlighted county indicates one or more documented
occurrences, although the species may be found elsewhere.
Canada Thistle, Cirsium
arvense (3KB color image)
Musk Thistle, Carduus
nutans (3KB color image)
Bull Thistle, Cirsium
vulgare (3KB color image)
Plumeless Thistle,
Carduus acanthoides (3KB color
image)
Canada thistle [Cirsium
arvense (L.) Scop.]
Though its name would indicate otherwise, Canada thistle is a
native of the Mediterranean region and southeast Europe. It
likely was introduced into North America in contaminated hay and
grain seed during early colonization in the 17th century. Canada
thistle also is found in China and Japan and has spread so
extensively that it is difficult to distinguish the plant's
original native range. Canada thistle has become very well
established in North America and is now considered a noxious weed
in at least 35 states and much of Canada. It is found throughout
North Dakota (Figure 26 - 3KB color map) and is considered naturalized.
Canada thistle has been classified into several varieties.
These varieties are distinguished mainly by leaf shape, size, and
abundance of leaf spines. Many ecotypes of Canada thistle also
exist and differ in growth, phenology, photoperiodism, and
susceptibility to herbicides and cultivation. A Canada thistle
variety has certain phenological characteristics but can be found
throughout the geographic range of the species, whereas an
ecotype differs from a variety because it is a population of
plants from a certain location or area with specific traits. For
example, leaf shape, head structure, and the number and size of
spines can differ with ecotype. Flower color can range from
purple to light lavender or even white (Figures 27 and 28). Stem
color also can differ from green to lavender (Figure 29).
However, plant response to herbicides or cultivation is not
related to any specific phenotypic variation. For instance, some
ecotypes are very resistant to herbicides and/or cultivation.
Figure 27.
Female purple flowering Canada thistle ecotype with a green
stem. (33KB color photo)
Figure 28. White
flowering form of Canada thistle which occurs in about 10% of
the population. (15KB color photo)
Figure 29. Canada
thistle ecotype with dark lavender stems and flowers. (34KB color photo)
Canada thistle grows best in the northern regions of North
America where temperature and rainfall are moderate. Canada
thistle rosettes (Figure 30) require at least 14 hours of
daylength to bolt and flower. Its growth is limited or stopped
when temperature exceed 85 degrees F for extended periods.
Although it will grow in a wide range of soils, Canada thistle
produces deeper roots in clay or muck soils than in sand or
gravel. The roots of Canada thistle have medicinal uses and have
been used to treat mouth diseases.
Figure 30. Canada
thistle rosette with spiny tips and shiny green wavy leaves. (15KB color photo)
Canada thistle usually grows 2 to 3 feet tall with alternate,
dark green leaves that vary in size (Figure 31). The leaves are
generally oblong, the length 3 to 5 times the width, usually
deeply lobed, and have spiny toothed edges. The leaf edge spines
vary in size and number according to variety. Canada thistle is a
perennial spreading both by seed and underground rhizomes. It
generally forms colonies and is found in cropland, roadsides, and
disturbed pasture soils. However, Canada thistle is not very
competitive in healthy turf.
Figure 31. Bolted
Canada thistle with alternate, waxy wavy leaves, and clusters
of flower heads. (31KB color photo)
Canada thistle is dioecious, that is male (Figure 32) and
female (Figure 27) flowers are produced
on different plants, so cross pollination is necessary for seed
production. Male flowers are often slightly smaller than female.
The flowers are numerous but small, usually less than 1 inch in
diameter. Canada thistle is the first thistle to flower in North
Dakota beginning in June through August. It is easily identified
by the small, numerous, clustered, often lilac colored and very
fragrant flowers. Involucre bracts are oval shaped with very
short spines.
Figure 32. Male
flower of Canada thistle with pollen-producing stamens. Heads
are usually less than 1 inch in diameter with short spines. (27KB color photo)
The flowers produce from 40 to 80 seeds per head. The smooth,
light brown to straw colored achenes are 0.1 to 0.2 inches long
with a conical point and are loosely attached to a tannish pappus
at the tip (Figure 25f - 20KB
color photo). Seeds mature rapidly, spread with pappus on
the wind, (Figure 33) and are able to germinate within 8 to 10
days after pollination.
Figure 33. Canada
thistle achenes are attached to a pappus which allows long
distance movement in the wind or on farm machinery, a major
method of movement to new areas. (29KB
color photo)
Red Admiral, viceroys and painted lady butterflies lay eggs on
Canada thistle, and the subsequent larvae feed on the leaves and
stems. However, only the painted lady butterfly builds up
populations high enough to eliminate an infestation. This
butterfly is generally found in southern states and will migrate
north only once every 8 to 11 years.
Bull thistle [Cirsium
vulgare (Savi) Tenore]
Bull thistle is the least serious of the introduced thistles
in North Dakota, and generally is found in the northern and
eastern counties of the state (Figure 26
- 3KB color map). Bull thistle is a
biennial and grows from a flat rosette of leaves the first year
to a flowering stem up to 5 feet tall the second (Figure 34).
Although the seed readily germinate, survival is low, and the
plant is often found growing singularly or only scattered in
pastures and wooded areas. Distinguishing characteristics of bull
thistle are the leaves and the broad prickly wings that line the
stem (Figure 35). Leaf margins are deeply toothed, and toothed
again (double dentate) with prominent stiff spines. The leaves
have prickly hairs above, especially along the midvein, and are
cottony below. The stems are very pubescent with dark purple
veins (Figure 36). The plant appears bushy rather than the
candelabra appearance of plumeless or Canada thistle.
Figure 34. Bushy
appearance of bull thistle with spiny conical shaped flower
heads. The plant is generally found growing solitary in
pastures and woodlands. (34KB color photo)
Figure 35. Double
dentate leaf of bull thistle with long stiff spines at each
tooth, prickly pubescence along the leaf mid-vein and a
broadly winged stem. The wings run completely along the stems
unlike musk thistle. (22KB color photo)
Figure 36. Bull
thistle stems are very pubescent and have dark purple veins. (25KB color photo)
Bull thistle heads are usually found singularly at the end of
each stem branch (Figure 34). The flowers are gumdrop shaped,
large (usually 2 or 3 inches tall), with long, stiff,
yellow-tipped spines (Figure 37). Bull thistle flowers from July
to September, which is somewhat later than other thistles in the
region. The flowers are usually purple but a rare white flowering
variety has been collected in the region.
Figure 37. Common
purple and rare white flowering bull thistle. The heads look
like large gumdrops with long stiff and very sharp spines. (30KB color photo)
The achenes are 0.1 to 0.15 inches long, glossy light brown to
pale yellow or white with narrow dark brown stripes (Figure 25g - 20KB color
photo). The rosette leaves of bull thistle are deeply
lobed and very pubescent with dark purple ribs (Figure 38).
Native Americans used bull thistle to treat hemorrhoids, which
they likely learned from French fur trappers. Bull thistle is
often the thistle species referred to as an edible plant. Many
parts are edible from the root to the flower. The petals were
used as chewing gum or tobacco by Native Americans.
Figure 38. Deeply
lobed and very pubescent bull thistle rosette. (30KB color photo)
Musk thistle (Carduus nutans
L.)
Musk thistle likely is the most easily identified invasive
thistle in North Dakota, yet many people confuse this plant with
either bull thistle or plumeless thistle. Musk thistle often
grows in excess of 6 feet tall and has very large flower heads
that tend to droop (Figure 39). The head has very characteristic
brown bracts that resemble a pine cone (Figure 40). Musk thistle
is a winter annual or biennial and has been found in the northern
half of North Dakota in dry areas or sandy and rocky soils (Figure 26 - 3KB color map).
Two subspecies of musk thistle which differ in the size of the
flower head and in foliage texture and pubescence are known in
North Dakota.
Figure 39. Musk
thistle grows 6 to 8 feet tall and is often found in dry
pastures. (60KB color photo)
Figure 40. Musk
thistle flower head is characterized by large brown bracts
that resemble a pine cone and the tendency to nod or lean
because of the large size of the flower. (49KB
color photo)
Musk thistle stems are usually very branched with spiny wings;
however, the wings are interrupted and not complete along the
stem as with bull or plumeless thistle (Figure 41). The leaves
are oblong to lanceolate, lobed to four-fifths of the width with
slender spines on the margin (Figure 42). Each lobe ends in a
prominent white or yellow spine. The leaves are dark green on top
with light green midribs and often a white margin. There is
generally little pubescence underneath, which helps to
distinguish musk thistle from plumeless thistle. However, the
subspecies C. nutans subsp. macrocephalus (Desf.)
has very pubescent leaves.
Figure 41. Stems of
musk thistle have wings that do not extend completely up and
down the stem which is smooth elsewhere. The heads often are
2 to 3 inches in diameter. (48KB color
photo)
Figure 42. Musk
thistle leaves are dark green, generally with little or no
pubescence and deeply lobed with small but sharp spines. The
subspecies macrocephalus does have
pubescent leaves. (24KB color photo)
The heads are borne singularly at the end of the stem and
droop or nod (Figure 41). The heads are often 2 to 3 inches
across and generally deep rose to violet, rarely purple. The
bracts are very broad and the outer ones are bent downward. Musk
thistle flowers from July to late September. Animals, especially
horses, eat the flower heads of musk thistle. It is not uncommon
to see almost completely "headless" plants in a horse
pasture or where elk feed.
The average musk thistle plant produces more than 10,000 seeds
per plant and under favorable conditions may produce 120,000
seeds per plant. The achenes are 0.15 to 0.2 inches long, glossy,
light brown with stripes and a light apical rim (Figure 25h - 16KB color
photo). Rosettes are dark green with a light green midrib
and often grow 2 feet in diameter or more (Figure 43). The
rosette leaves are usually smooth and lacking pubescence.
Figure 43. Musk
thistle rosette which often grows 2 feet or more in diameter.
(68KB color photo)
Plumeless thistle (Carduus
acanthoides L.)
Plumeless thistle tends to be shorter than other invasive
thistles and generally reaches 1 to 4 feet tall (Figure 44).
Plumeless thistle is a winter annual or biennial and is generally
found only in eastern North Dakota (Figure
26 - 3KB color map). Plumeless thistle
can become very weedy and form dense colonies, especially along
waterways, ditches, and roadsides in summers following wet falls.
Plumeless thistle is seldom found in cultivated fields, even when
infestations are nearby in roadsides or pastures.
Figure 44. Flowering
plumeless thistle showing spiny winged stems that completely
extend up and down the stem unlike musk thistle. (39KB color photo)
Plumeless thistle stems are winged and very branched giving
the plant a candelabrum appearance (Figure 44). The wings are
very spiny and are continuous along the stem and not interrupted
like musk thistle (Figure 45). The leaves are more deeply lobed
and narrower thanmusk thistle and very pubescent underneath
(Figure 46). Each lobe has one to three pointed marginal spines
which are short but very sharp (Figure 47).
Figure 45. Plumeless
thistle is very branched and very spiny, the most prickly of
all the thistles in North Dakota. (26KB
color photo)
Figure 46. Plumeless
thistle leaves are more deeply lobed than musk thistle and
have much more pubescence. (28KB color
photo)
Figure 47. Each leaf
lobe of plumeless thistle has one to three very sharp stiff
spines with a white margin that resembles holly. (26KB color photo)
The heads are small (0.5 to 1 inch in diameter) but very
numerous and pink to purple in color or very rarely white (Figure
48). The bracts beneath the flowers are very narrow and resemble
spines. The heads can be singular or in clusters of 2 to 5. The
achenes are small, grey to light brown with a distinct, light
apical collar and slightly curved (Figure
25i - 20KB color photo). Plumeless
thistle flowers from May to August.
Figure 48. Plumeless
thistle head with short, very sharp spines on the bracts. (38KB color photo)
Rosettes of plumeless thistle resemble those of musk thistle,
except they are more deeply lobed and much more pubescent (Figure
49). Plumeless thistle rosettes have wavy leaves with yellow
spines along the white-colored leaf margins.
Figure 49. Plumeless
thistle rosette, which is similar in appearance to musk
thistle except much more pubescent, especially on the
underside of the leaves. (67KB color
photo)
Major References
Densmore, F. 1974. How Indians use wild plants for food,
medicine and crafts. Dover Publications Inc. New York, NY 10014.
Great Plains Flora Association. 1977. Atlas of the flora of
the Great Plains. Iowa State University Press. Ames, IA 50010.
Great Plains Flora Association. 1986. The flora of the Great
Plains. University Press of Kansas. Lawrence, KS 66049.
Kindscher, K. 1987. Edible wild plants of the prairie: an
ethnobotanical guide. University Press of Kansas, Lawrence, KS
66049.
Kindscher, K. 1992. Medicinal wild plants of the prairie: an
ethnobotanical guide. University Press of Kansas, Lawrence, KS
66049.
Moore, R. J., and C. Frankton. 1974. The thistles of Canada.
Canada Dept. of Ag. Monogr. 10. Ottawa, Canada K1A 0C7.
Steiner, R. P. 1986. Folk medicine: the art and the science.
American Chemical Society. Washington, D.C. 20541.
Western Society of Weed Science. 1991. Weeds of the West.
Pioneer of Jackson Hole, Jackson, WY 83001.
All photographs by Rodney G. Lym.
W-1120, October 1996
NDSU Extension Service, North Dakota State University of
Agriculture and Applied Science, and U.S. Department of
Agriculture cooperating. Sharon D. Anderson, Director, Fargo,
North Dakota. Distributed in furtherance of the Acts of Congress
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