WEED IDENTIFICATION Group 1

Asteraceae: Rhaponticum repens (Acroptilon repens)

List B

Russian knapweed

List B

Asteraceae: Cirsium arvense

List B

Canada thistle

List B

Asteraceae: Helianthus annuus

common sunflower

Asteraceae: Taraxacum officinale

dandelion

Asteraceae: Lactuca serriola

prickly lettuce

Amaranthaceae: Amaranthus palmeri

Palmer amaranth

Amaranthaceae: Amaranthus retroflexus

redroot pigweed

Boraginaceae: Cynoglossum officinale

List B

houndstongue

List B

(List B species)

Asteraceae: Rhaponticum repens (Acroptilon repens)

Russian knapweed

(List B species)

Asteraceae: Cirsium arvense

Canada thistle

Differences Between: Cirsium arvense & Rhaponticum repens

Knapweeds (Rhaponticum repens) lack the spiny leaves that thistles have (Cirsium arvense)

Asteraceae: Helianthus annuus

common sunflower

Asteraceae: Taraxacum officinale

dandelion

Asteraceae: Lactuca serriola

prickly lettuce

Amaranthaceae: Amaranthus palmeri

Palmer amaranth

Amaranthaceae: Amaranthus retroflexus

redroot pigweed

Boraginaceae: Cynoglossum officinale

houndstongue

Asteraceae - Compositae, the aster family

→ -Annual, biennial, perennial

Floral characteristics

-Head inflorescence: tiny florets combined together to make a singular head or disk

-Comprised of ray and disc florets

-Heads can be single or arranged in racemes, corymbs, or panicles.

Seeds and Fruit

-Achene or cypsela

Cotyledon

-Ovate or lance-shaped

Stems

-Herbaceous, cylindrical, typically with glandular hairs

Roots

-Can be a taproot or fibrous

Leaves

-Typically alternate or in a basal rosettes

-Can be simple or compound in shape

-Milky sap

Inflorescence Type

Amaranthaceae - the pigweed family

→Annual or Perennial

Floral characteristics

-Flowers are typically green with scarious bracts

-The inflorescence can be solitary, in spikes, heads or racemes

-Sepals and stamens typically in groups of 4-5.

-Stamens united by filaments 

Seeds

-Pyxis or utricle

-Rarely drupe or berries

Cotyledon

-Typically ovate in shape

-Dull green on the top of leaf and red underneath, hairless,

Stems

- Are typically herbaceous but sometimes woody, erect or straggling, branched

-Typically reddish tint to lower stems

Roots

-Typically a branched tap root

Leaves 

-Alternate or opposite

-Simple

Which of these weeds are native to Colorado?

Rhaponticum repens (Acroptilon repens)	Russian knapweed
Cirsium arvense	Canada thistle
Helianthus annuus	common sunflower
Taraxacum officinale	dandelion
Lactuca serriola	prickly lettuce
Amaranthus palmeri	Palmer amaranth
Amaranthus retroflexus	redroot pigweed
Cynoglossum officinale	houndstongue

Helianthus annuus → common sunflower

Amaranthus palmeri → Palmer amaranth

(Native to desert regions of the southwest US and northern Mexico)

Amaranthus retroflexus→ redroot pigweed

Cynoglossum officinale: houndstngue

Which weeds are naturalized to Colorado?

Rhaponticum repens (Acroptilon repens)	Russian knapweed
Cirsium arvense	Canada thistle
Helianthus annuus	common sunflower
Taraxacum officinale	dandelion
Lactuca serriola	prickly lettuce
Amaranthus palmeri	Palmer amaranth
Amaranthus retroflexus	redroot pigweed
Cynoglossum officinale	houndstongue

Taraxacum officinale→ dandelioln

Was introduced to the US as a food crop but is now considered naturalized and a weed in most areas

Palmer amaranth (Amaranthus palmeri) : defining features

redroot pigweed (Amaranthus retroflexus) : defining features

Rhaponticum repens (Acroptilon repens)

Russian knapweed

Cirsium arvense
Canada Thistle

Taraxacum officinale
dandelion

Lactuca serriola

prickly lettuce

Amaranthus palmeri
Palmer amaranth

Amaranthus retroflexus
redroot pigweed

Cynoglossum officinale

houndstongue

Helianthus annuus

common sunflower

What weeds (in Group 1) belong to the Asteraceae family?

• Rhaponticum repens (Russian knapweed)

• Cirsium arvense (Canada thistle)

• Helianthus annuus (common sunflower)

• Taraxacum officinale (dandelion)

• Lactuca serriola (prickly lettuce)

What weeds (in Group1) belong to the Amaranthaceae family?

• Amaranthus palmeri (Palmer amaranth)

• Amaranthus retroflexus (redroot pigweed)

What weeds (in Group1) belong to the Boraginaceae family?

• Cynoglossum officinale (houndstongue)

Which weeds (Group 1) are List B species?

• Rhaponticum repens (Russian knapweed)

• Cirsium arvense (Canada Thistle)

• Cynoglossum officinale (houndstongue)

Rhaponticum repens: Identification

Russian knapweed

• Perennial
• Root crowns have a brown to black, scaly appearance

• Reproduce by adventitious buds on roots

• Allelopathic compounds prevent plant competition (not proven)

• Research shows that roots can survive 75+ years underground

Cirsium arvense: Identification

Canada thistle

• Creeping roots (rhizomes)

•Flowers are pink to purple

•Spineless, scaleless bracts

•Leaves have spiny toothed margins

Helianthus annuus: Identification

common sunflower

• Annual

• Leaves are large,ovate to triangular, sandpapery and up to 12 in. long

• Stems erect, coarse, branched, stiff and upright

• Can be 5-10 ft. tall

Taraxacum officinale: Identification

dandelion

• Perennial

• Leaves are clustered in a rosette at the base of the plant; margins are deeply serrated

• Stems hollow, hairless

• Strong taproot is capable of penetrating the soil to a depth of 10-15 ft.

• Flowering stalks terminate in an inflorescence that contains 100 to 300 ray flowers

• Each ray flower grows singly on the stem. (Not to be confused with ‘false dandelions’ which have many flowers per stem)

Lactuca serriola: Identification

prickly lettuce

• Annual
• Leaves alternate

• Conspicuous, white midvein; underside of the vein covered with many prickles

• Stems 1.5-6 ft. tall; erect,branches, with white latex sap

• Flowers yellow with dark blue stripe on lower side

Amaranthus palmeri: Identification

Palmer amaranth

• Annual

• Dioecious (male & female plants)

• Petiole length is longer than the leaf

• Leaves are ovate or diamond shape

• Some leaves have “V” shaped watermark

• Stems erect, branching and hairless

• Usually 6-8 ft. tall

Amaranthus retroflexus: Identification

redroot pigweed

● Annual, taproot

● Monoecious

● Leaves delta to lance-shaped; leaf margin: entire
● Fine hairs on stem

● Prominent veins often reddish

● Upper portion of root are red to pink

● Average height 3 ft, max. height 10 ft

Cynoglossum officinale: Identification

houndstongue

● Biennial forb

● Purple flower

● Reproduces by seed

● Stem is erect, stout, heavy,single flowering stem.

● Thick, black woody taproot.

● Seeds 1/3 in long with, with outer surface covered with short barbs.

● Contains alkaloids (may cause liver cells to stop reproducing).

What weeds (i n Group 1) are List B species?

• Rhaponticum repens → (Russian knapweed)

• Cirsium arvense → (Canada thistle)

• Cynoglossum officinale→ (houndstongue)

What is a List B Species?

Weeds in Colorado that are established in some areas of the state but not yet widespread across the entire state. For these species, management strategies, which are determined by the Colorado Commissioner of Agriculture, involve eradication in uninfested areas and containment or suppression in more established areas to prevent further spread