Weed Information: Asclepias subverticillata (milkweed, western whorled)
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Asclepias subverticillata (milkweed, western whorled)

Family: Asclepiadaceae

Description

This species is easily distinguished from the other western milkweeds by its narrow (1-5) mm linear leaves and white flowers but is very similar to eastern whorled milkweed (Asclepias verticillata). It can be distinguished from Asclepias verticillata by the presence of branches in the axillary inflorescences of this species.

Characteristics

Flower Color
  • Green
  • Purple
  • White
  • Multi-colored
Inflorescence Type (How the flowers are arranged on the plant)
  • Simple umbel
Number of Petals
  • 5 petals
Petal Separation
  • United at base only (<25% length)
  • United from 25% - 75% length
Petal Tip
  • Pointed
  • Rounded
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
  • 8 mm (.32 inch)
Flower Width (Head width in the Asteraceae)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
Number of Sepals
  • 5 sepals
Sepal Separation
  • Completely free to base
  • United at base < 25% length
Sepal Tip
  • Pointed
Flower Sex
  • Bisexual (perfect)
Number of Styles
  • 1 style
Number of Stamens
  • 5 stamens
Stamens Attached to the Petals
  • Stamens attached to the petals
Stamens Connate (united)
  • Filaments united, monodelphous

Carpel Separation
  • Carpels united (or one)
  • Carpels separated
Number of Carpels
  • 2 carpels
Ovary Position
  • Superior (hypogynous)
Fruit Type
  • Follicle
Fruit Length at Maturity
  • 6.0 cm (2.4 inches)
  • 7.0 cm (2.8 inches)
  • 8.0 cm (3.2 inches)
  • 9.0 cm (3.6 inches)
  • 1.0 dm (4.0 inches)
  • 1.5 dm (6.0 inches)
Fruit Width at Maturity
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
  • 8 mm (.32 inch)
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • Whorled 3 per node
  • Whorled 4 per node
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Pinnate
Petiole (leaf stem) Blade Ratio
  • Petiole absent (leaf sessile)
Leaf Length (blade PLUS petiole)
  • 2 - 4 cm (.80 - 1.60 inches)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
Leaf Width
  • 1 - 5 mm (.04 - .20 inch)
Leaf Shape (simple leaves only)
  • Linear or filiform
Succulence
  • Succulent
Leaf or Leaflet Margin
  • Entire
Leaf or Leaflet Blade Base
  • Acute (cuneate)
  • Acuminate (attenuate)
Leaf or Leaflet Tip
  • Acute
Leaf or Leaflet Blade Surface
  • Glabrous (NO hairs)
  • Puberulent

Milky Juice
  • Juice milky
Woodiness
  • Herbaceous
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
Life Cycle
  • Perennial
Growth Habit (while flowering)
  • Erect, columnar (narrow)
Plant Height at Maturity
  • 4 - 6 dm (1.3 - 2.0 feet)
  • 6 - 8 dm (2.0 - 2.6 feet)
  • 8 - 10 dm (2.6 - 3.3 feet)
Wind Dissemination
  • Fruit, seed, or spore wind borne
Moisture Regime
  • Seasonally saturated
  • Mesic
Chlorophyll
  • Present

Stem Cross Section
  • Round
Flowering Stem Leaves
  • Stem uniformly leafy
Main Stem Branches
  • Main stem branched

Root or Vegetative Propagule
  • Rhizomatous

US State
  • Kansas
  • Missouri
  • Texas
  • Arizona
  • Colorado
  • New Mexico
  • Nevada
  • Oklahoma
  • Utah

  • An Illustrated Guide To Arizona Weeds, 1972 (ISBN 0-8165-0288-9) 338 pages. See page: 228
  • Field Guide To The Common Weeds Of Kansas, 1983 (ISBN 0-7006-0233-X) See page: 83
  • Weed Seeds of the Great Plains, 1993 University of Kansas# 92-125-B ISBN# 0-7006-0651-3 See index #: 141
  • Weeds, 1955 (1980) Walter Conrad Muenscher, ISBN# 0-8014-1266-8 See page: 343
  • Weeds of Colorado, 1990 Cooperative Extension, Colorado State Univ. Bulletin 521A, See page: 115
  • Weeds of the West, 1992 (ISBN 0941570-13-4) See page: 40
  • Weeds of the West, 2000 (ISBN 0941570-13-4) See page: 40
  • Weeds of Utah, 1971 UAES Special Report 21, See page: 66
  • Listed as a `Weed` by the Biota of North America Program, 2008 X
  • Listed in the WSSA Composite List of Weeds X
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