• You are here:
• Full Key
• All other flowering non-woody plants
• Daisies, goldenrods, and other aster family plants
• Parthenium hysterophorus

Parthenium hysterophorus — Santa Maria feverfew

Facts

Santa Maria feverfew is probably native to Mexico, Central America and parts of South America, but it has expanded its range around the world. It has become one of the most feared weeds on earth due to its health effects on humans and cattle (asthma, bronchits, dermatitis, and hay fever), as well as its allellopathic (toxic, growth-inhibiting) effects on other plants, including crops. Nevertheless, it is often used in herbal medicine to treat conditions including tuberculosis, dysentery and ague, and animal studies have shown antitumor activity in mice. It is uncommon in New England.

Habitat

Anthropogenic (man-made or disturbed habitats), meadows and fields

Characteristics

• Flowers

  Bract cycle number

  there are two main cycles of bracts

  Bract outer side hairs

  the bracts are not hairy on their outer surfaces

  Bract separation

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

  Bract texture

  • the bracts appear thin, flexible and nearly translucent
  • the bracts have a similar texture to a leaf

  Disk flower color

  • white
  • yellow

  Disk flower lobe number

  5

  Disk flower number

  • 11-20
  • 21-50
  • more than 50

  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

  Disk width

  3–5 mm

  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, each flower has a single enlarged lobe or strap

  Flower head platform

  the base has papery scales on it

  Flower head position

  some or all the flower heads are grouped in clusters of two or more

  Flower head profile

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

  Flower head shape

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

  Flower head width

  4–5 mm

  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

  3–12 mm

  Inflorescence branching (Solidago)

  NA

  Inflorescence shape

  • the inflorescence is flat-topped in profile
  • the inflorescence is not flat-topped but appears rounded, with some flower heads distinctly higher than others

  Number of bracts at flower head base

  10–16

  Ovary cross-section

  • the ovary has five or more corners in cross-section
  • the ovary is compressed (flattened)

  Ovary profile

  • in profile, the ovary is another shape
  • in profile, the ovary is lance-shaped, but widest above the middle
  • in profile, the ovary is roughly egg-shaped, but widest above the middle

  Peduncle hairs

  the peduncles are hairy

  Peduncle length

  1–15 mm

  Peduncle orientation

  the flower heads are held upright, or slightly angled outwards

  Ray flower color

  • white
  • yellow

  Ray flower reproductive parts

  the ray flowers have carpels or stamens, but not both

  Ray flowers

  6-10

  Ray length

  2.5–4 mm

  Reproductive system

  the flowers on the plant may have either carpels or stamens, but always in separate flowers

  Style branch number

  the style has one branch

  Swelling at base of flower head

  the peduncles are not swollen, or only slightly

  Width of flower head base

  3–12 mm

• Fruits or seeds

  Dispersal unit

  the seeds fall off or are dispersed separately from one another

  Number of pappus parts

  • 0
  • 3

  Ovary length in developed fruit

  1.5–3.5 mm

  Seed hair tuft bases

  NA

  Seed hair tuft color

  NA

  Seed hair tuft details

  NA

  Seed hair tuft length

  0.5–1 mm

  Seed hair tuft tips

  NA

  Seed hairs uniform

  NA

  Seed tuft scale number

  0–3

  Seed tuft type

  the pappus is made of flat scales that are not split or frayed at the tips

  Top of disk flower ovary

  NA

  Tuft or plume on fruit

  there is no plume, or the plume is made up of scales, awns, a crown, or a rim

• Glands or sap

  Leaf blade glands

  the leaf blades have glandular (translucent) dots or scales

  Sap

  the sap is clear and watery

• 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

  Underground organs

  there are only slender roots on the plant

• Leaves

  Final leaf segment length (compound lvs only)

  3–50 mm

  Final leaf segment width (compound lvs only)

  2–15 mm

  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
  • basal: the leaves are growing only at the base of the plant

  Leaf blade base

  • the leaf has a distinct petiole
  • the leaf has no petiole

  Leaf blade base shape

  the base of the leaf blade is cuneate (wedge-shaped, tapers to the base with relatively straight, converging edges), or narrow

  Leaf blade edges

  • the edge of the leaf blade has lobes, or it has both teeth and lobes
  • the edge of the leaf blade has no teeth or lobes

  Leaf blade hairs

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

  Leaf blade length

  30–180 mm

  Leaf blade shape

  the leaf blade is oblanceolate (lance-shaped, but with the widest point above the middle of the leaf blade)

  Leaf blade veins

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

  Leaf blade width

  10–90 mm

  Leaf disposition

  • the leaves are nearly similar in size, prominence of teeth, and length of stalks throughout the stem
  • the lower leaves are larger, toothier, and/or on longer stalks than the upper leaves

  Leaf spines

  there are no spines on the leaf edges

  Leaf stalk

  • the leaves have leaf stalks
  • the leaves have no leaf stalks, but attach directly to the stem

  Leaf stalk length

  Up to 20 mm

  Leaf type

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

  Leaflet number

  0

  Specific leaf type

  • the leaf has a row of two or more lobes on each side of the central axis
  • the leaf has a row of two or more lobes on each side of the central axis, and each lobe itself has rows of lobes on each side of the lobe's central axis

• Place

  Habitat

  terrestrial

  New England state

  • Connecticut
  • Massachusetts

  Specific habitat

  • man-made or disturbed habitats
  • meadows or fields

• Stem, shoot, branch

  Stem internode hair direction

  the hairs are pressed flat against the plant, pointing either towards the plant's tip or towards it's base

  Stem internode hair type

  at least some of the hairs on the stem are tangled, matted or woolly

  Stem internode hairs

  the stem has hairs between the nodes

Wetland status

Occurs only in non-wetlands. (Wetland indicator code: UPL)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae