Weed Information: Toxicodendron rydbergii (poison-ivy, Rydberg's)
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Toxicodendron rydbergii (poison-ivy, Rydberg's)

Family: Anacardiaceae

Description

The taxonomy of this group is extremely difficult as the species have been placed in the genus Rhus as well as the genus Toxicodendron. There are also many subspecies and varieties, some of which seem to hybridize. The plants vary from low shrubs to climbing vines which helps to account for the fact that several species are referred to as both `poison-oak` and `poison-ivy.` An interesting fact is that both sensitivity and immunity vary with time as well as with individuals. In other words, someone who is immune today, may be susceptible tomorrow!

Characteristics

Flower Color
  • Yellow-green
  • Green
  • White
Inflorescence Type (How the flowers are arranged on the plant)
  • Axillary cluster
  • Panicle
Number of Petals
  • 5 petals
Petal Separation
  • Completely free to base
Petal Tip
  • Pointed
  • Rounded
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • 1 mm (.04 inch)
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
Flower Width (Head width in the Asteraceae)
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
Number of Sepals
  • 5 sepals
Sepal Separation
  • Completely free to base
Sepal Tip
  • Pointed
  • Rounded
Flower Sex
  • Bisexual (perfect)
Number of Styles
  • 1 style
Number of Stamens
  • 5 stamens
Stamens Attached to the Petals
  • Stamens NOT attached to the petals
Stamens Connate (united)
  • Filaments or anthers NOT united

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 1 carpel
  • 3 carpels
Ovary Position
  • Superior (hypogynous)
Fruit Type
  • Berry, white
  • Berry, yellow\orange\brown
Fruit Length at Maturity
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
Fruit Width at Maturity
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
  • 7 mm (.28 inch)
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • Alternate
Leaf Type
  • Trifoliolate (3 leaflets)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Pinnate
Petiole (leaf stem) Blade Ratio
  • Petiole 25% - 75% total length
Leaf Length (blade PLUS petiole)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
  • 2 - 4 dm (8.0 - 16.0 inches)
Leaf Width
  • 4 - 10 cm (1.6 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
  • 2 - 4 dm (8.0 - 16.0 inches)
Leaf or Leaflet Margin
  • Dentate
  • Undulate (sinuate, repand)
Leaf or Leaflet Blade Base
  • Acute (cuneate)
  • Rounded
Leaf or Leaflet Tip
  • Rounded (obtuse)
Leaf or Leaflet Blade Surface
  • Glabrous (NO hairs)
Succulence
  • Not succulent

Milky Juice
  • Juice milky
Woodiness
  • Woody
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
Life Cycle
  • Perennial
Growth Habit (while flowering)
  • Erect, columnar (narrow)
  • Erect, spherical (bushy)
  • Climbing vine
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)
  • 1 - 1.5 meters (3.3 - 5.0 feet)
  • 1.5 - 2.0 meters (5.0 - 6.6 feet)
Wind Dissemination
  • Not wind disseminated
Moisture Regime
  • Seasonally saturated
  • Mesic
  • Arid
Chlorophyll
  • Present

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

Root or Vegetative Propagule
  • Tap Root

US State
  • Connecticut
  • Illinois
  • Kansas
  • Massachusetts
  • Maine
  • Michigan
  • North Carolina
  • New Hampshire
  • New York
  • Ohio
  • Pennsylvania
  • Texas
  • Virginia
  • Wisconsin
  • West Virginia
  • Indiana
  • Maryland
  • Rhode Island
  • Vermont
  • Arizona
  • Colorado
  • Iowa
  • Idaho
  • Minnesota
  • Montana
  • North Dakota
  • New Mexico
  • Nevada
  • Oklahoma
  • Oregon
  • South Dakota
  • Utah
  • Washington
  • Wyoming
  • Nebraska
Canadian Province or Territory
  • British Columbia
  • New Brunswick
  • Nova Scotia
  • Ontario
  • Prince Edward Island
  • Quebec
  • Alberta
  • Manitoba
  • Saskatchewan
  • Yukon

  • Identification Guide to the Weeds of Quebec, 1999 (ISBN# 2-89457-174-7) See page: 214
  • South Dakota Weeds, 1967 South Dakota State University, See page: 119
  • South Dakota Weeds 2002 South Dakota Dept. of Ag. 523 E. Capitol, Foss Bldg. Pierre, South Dakota 57501 See page: 138
  • Weeds, 1955 (1980) Walter Conrad Muenscher, ISBN# 0-8014-1266-8 See page: 306
  • Weeds and Poisonous Plants of Wyoming and Utah 1987 (ISBN 0-941570-06-1) See page: 228
  • Weeds of Colorado, 1990 Cooperative Extension, Colorado State Univ. Bulletin 521A, See page: 103
  • Weeds of Nebraska and the Great Plains, 1994 (ISBN 0939870-00-4) See page: 44
  • Listed as a `Weed` by the Biota of North America Program, 2008 x
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