Sunflower Family

Asteraceae (ass-ter-AY-see-ee)

Iconic Features

• Composite heads of many flowers
• Disk and/or straplike flowers

Description (Jepson)

• Eudicotyledons (eudicots) – a major lineage of flowering plants including most plants traditionally described as dicots and generally characterized by
  • 2 seed leaves (dicotyledon)
  • Netted (reticulate) leaf venation
  • Flower parts in fours and fives
  • Pollen grains with 3 pores (tricolpate)
  • Vascular bundles in stem arranged in a ring
  • Taproot system
• Mostly annuals and herbaceous perennials
  • Also can be shrubs, vines, and trees
• Leaves
  • Simple (not divided into leaflets) to compound (divided into leaflets)
  • Basal and/or cauline (on the stem)
  • Alternate (1 leaf at each junction with stem) or opposite (2 leaves at each junction with stem) or, rarely, whorled (3 or more leaves at each junction with stem)
• Flowers
  • Inflorescence (flower arrangement) is in densely packed heads (capitulum/a) of dozens to hundreds of individual flowers
    • Heads may appear singly or in a variety of secondary arrangements
  • Flowerheads come in 4 basic forms (with many variations)
    • Radiate Heads have both disk and ray flowers (e.g. mule’s ears)
      • 5-lobed star- or tube-shaped disk flowers cluster in the center
      • 3-lobed strap-like ray flowers rim the edge
    • Ligulate (Liguliflorous) Heads have only 5-lobed, strap-like flowers (e.g. dandelion)
    • Discoid Heads have only 5-lobed star- or tube-shaped disk flowers (e.g. mugwort)
    • Disciform Heads have disk and disk-like flowers (e.g. everlasting)
      • 5-lobed star- or tube-shaped disk flowers cluster in the center
      • Disk-like flowers with minute or missing rays rim the edge
  • Flowers are protandrous (male flower parts mature before female parts) and employ a strategy of secondary pollen presentation
    • Anthers (pollen-producing part of the stamen/male structure) are fused into a column facing toward and surrounding the pistil (female flower part)
    • When still immature, the style (pistil stalk) elongates, pushing ripe pollen up through the anther column to present to pollinators
    • When the flower’s own pollen is depleted, the style splits to receive pollen from other flowers
    • This strategy is believed to reduce the chance of self-pollination
  • Sepals (protective covering for bud) are absent or modified into a pappus, composed of bristles or scales (e.g. the tufts of a dandelion seed)
  • Ovary inferior (below the attachment of other flower parts)
  • Composite head is usually held in a whorl of bracts (modified leaves), called an involucre
    • Individual bract is called a phyllary
    • Phyllaries (pattern, shape, ranks, etc.) is often diagnostic
  • Individual flowers lack stems; instead they are attached to a platform called a receptacle
• Fruit is an achene (a single-seeded, dry fruit that does not split open), often with pappus attached to aid dispersal

Notes

• Approximately 23,000 species worldwide, in many habitats
  • Largest family of vascular plants in California (Jepson eFlora) and of eudicots globally
  • Found everywhere except Antarctica and the extreme Arctic
• Great variety of horticultural, economic, and medicinal uses
• Scientific name from the included genus Aster, from the Greek for “star”
  • An early name for this family was Compositae because what appears to be an individual flower is actually a composite of flowers, as in a bouquet
  • Other common names are the Daisy or Composite family
• Due to its size, the Sunflower family is traditionally broken into a number of subgroups, including tribes; here are some tribes and representative plants
  • Mayweed Tribe (Anthemideae) – yarrow (Achillea millefolium), sagebrush (Artemisia species), pineapple weed (Chamomilla sauveolens)
  • Aster Tribe (Astereae) – asters (Aster species), gumplants (Grindelia species), coyote brush (Baccharis pilularis)
  • Chicory Tribe (Cichorieae) – California dandelion (Agoseris grandiflora), hawkweeds (Hieracium species), silver puffs (Uropappus lindleyi)
  • Thistle Tribe (Cynareae) – star-thistles (Centaurea species), Italian thistle (Carduus pycnocephalus)
  • Sunflower Tribe (Heliantheae) – mule ears (Wyethia species), tarweeds (Madia species), goldfields (Lasthenia species)
  • Everlasting Tribe (Inuleae) – cudweed (Pseudognaphalium californicum), stinkwort (Dittrichia graveolens)
• Represented by 94 species at Edgewood

See General References

Specific References

Candeias, M. 2019, Sep. 22. An intriguing way of presenting one’s pollen. In Defense of Plants.

Mason, J. 2004. [Sunflower family flower-head illustrations, adapted]. In T. Corelli, Flowering Plants of Edgewood Natural Preserve (2nd. ed.). Monocot Press, Half Moon Bay, California. (c) CC BY NC 3.0.

Browse Some Edgewood Plants in this Family