Sunflower Family

California Aster © KKorbholz

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
Radiate Head (L), Ligulate Head (M), Discoid Head (R) © JMason

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. Asteraceae — Sunflower family characteristics [Illustration of flower heads, adapted]. 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