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• Asteraceae Group 3
• Iva
• Iva annua

Iva annua — rough marsh-elder

Facts

Not reaching farther north than Pennsylvania in its native range, rough marsh-elder is non-native in New England, but a common annual elsewhere in North America. Like ragweed, it is a source of allergenic airborne pollen. Rough marsh-elder was apparently cultivated by prehistoric Native Americans (Scioto Hopewell) as a seed crop, based on archeological remains documenting increases in achene size by 2000 BC.

Habitat

Anthropogenic (man-made or disturbed habitats)

Characteristics

• Flowers

  Bract color

  the bracts are not colored or tinged with pink, red or purple

  Bract cycle number

  there is one main cycle of bracts

  Bract margins

  there are fine hairs along the bract margins

  Bract outer side hair type

  the bracts are hairy, with simple hairs on their outer surface

  Bract outer side hairs

  the bracts are hairy on their outer surfaces

  Bract separation

  the bracts appear completely unconnected to one another on all flower heads

  Bract spines

  the bracts have no spines

  Bract texture

  the bracts have a similar texture to a leaf

  Bracts

  the bracts in separate cycles are similar or gradually changing from the outer to inner cycles

  Disk flower color

  white

  Disk flower lobe number

  5

  Disk flower proportions

  NA

  Disk flower reproductive parts

  the disk flower has either only pollen- or only seed-producing parts

  Disk flower shape

  the disk flower is tube-shaped (cylindrical), or gradually widening like a funnel

  Flower head number

  each flowering stem has four or more flower heads on it

  Flower head outer flowers

  at the outer edge of the flower head, the flowers have no enlarged lobe or strap, and are of similar size as those in the center of the disk

  Flower head platform

  the base has papery scales on it

  Flower head profile

  • the disk is flat or nearly flat across the top
  • the disk is rounded across the top

  Flower head shape

  the flower head is hemispherical (like the bottom half of a sphere)

  Flower type in flower heads

  the flower head has tubular disk flowers in the center and ray flowers, these often strap-shaped, around the periphery

  Height of flower head base

  1.5–4 mm

  Inflorescence branching (Solidago)

  NA

  Inflorescence shape

  • the flower heads grow in clusters from the axils of the branches or leaves
  • the inflorescence is not flat-topped but appears rounded, with some flower heads distinctly higher than others

  Number of bracts at flower head base

  3–15

  Ovary cross-section

  the ovary is compressed (flattened)

  Ovary hair type

  the ovary has hairs on it, but the hairs have no glands

  Ovary hairs

  the ovary has hairs on it

  Ovary profile

  in profile, the ovary is roughly egg-shaped, but widest above the middle

  Peduncle length

  0–1 mm

  Ray flower color

  NA

  Ray flower reproductive parts

  NA

  Ray flowers

  NA

  Reproductive system

  all the flowers on the plant contain both carpels and stamens

  Smaller bracts at base of bracts

  there is a cycle of much smaller bracts outside the cycle of larger and longer bracts

  Style branch number

  there are no obvious branches on the style

  Style branches

  the style branch is narrow at the tip, or the style branches are narrow at the tips

  Width of flower head base

  3–5 mm

• Fruits or seeds

  Number of pappus parts

  NA

  Ovary length in developed fruit

  2–3 mm

  Seed hair tuft bases

  NA

  Seed hair tuft color

  NA

  Seed hair tuft details

  NA

  Seed hair tuft tips

  NA

  Seed hairs uniform

  NA

  Seed tuft type

  there is no pappus on the ovary

  Top of disk flower ovary

  NA

  Tuft or plume on fruit

  NA

• Glands or sap

  Leaf blade glands

  the leaf blades have glandular (translucent) dots or scales

  Ovary glands

  there are glands on the ovary surface

• Growth form

  Growth form

  the plant has one or more free-standing stems

  Plant lifespan

  the plant is annual, it lacks evidence of previous years' growth

  Spines on plant

  the plant has no spines

• Leaves

  Hairs on underside of leaf blade

  the underside of the leaf is fuzzy or hairy

  Leaf arrangement

  • alternate: there is one leaf per node along the stem
  • opposite: there are two leaves per node along the stem

  Leaf blade base

  the leaf has a distinct petiole

  Leaf blade base shape

  • the base of the leaf blade is rounded
  • the base of the leaf blade is truncate (ends abruptly in a more or less straight line as though cut off)

  Leaf blade edges

  the edge of the leaf blade has teeth

  Leaf blade flatness

  the leaf is flat (planar) at the edges

  Leaf blade hairs

  the leaf blade has simple hairs with no glands, and not tangled or wooly

  Leaf blade length

  30–150 mm

  Leaf blade shape

  • the leaf blade is elliptic (widest near the middle and tapering at both ends)
  • the leaf blade is lanceolate (lance-shaped; widest below the middle and tapering at both ends)
  • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
  • the leaf blade is triangular, with the stalk or attachment point on one of the sides

  Leaf blade tip

  • the tip of the leaf blade is acuminate (tapers to a long, thin point)
  • the tip of the leaf blade is acute (sharply pointed)

  Leaf blade veins

  the leaf blade has one main vein running from the base towards the tip

  Leaf blade width

  8–80 mm

  Leaf disposition

  the leaves are nearly similar in size, prominence of teeth, and length of stalks throughout the stem

  Leaf spines

  there are no spines on the leaf edges

  Leaf stalk length

  5–30 mm

  Leaf type

  leaves are simple (i.e., lobed or unlobed but not separated into leaflets)

  Specific leaf type

  the leaves are simple (i.e., lobed or unlobed but not separated into leaflets

• Place

  Habitat

  terrestrial

  New England state

  • Maine
  • Massachusetts

  Specific habitat

  man-made or disturbed habitats

• Stem, shoot, branch

  Leaves on stem

  there is at least one full leaf above the base of the flowering stem

  Stem internode hair direction

  • NA
  • the hairs are pressed flat against the plant, pointing either towards the plant's tip or towards it's base
  • the hairs point mostly upwards to outwards

  Stem internode hair type

  • the hairs on the stem are plain, without glands or branches, and not tangled
  • the stem has no hairs between the nodes

  Stem internode hairs

  • the stem has hairs between the nodes
  • the stem has no hairs between the nodes

Wetland status

Occurs in wetlands or non-wetlands. (Wetland indicator code: FAC)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae