Family Description
The Aster family is a large group of dicotyledonous herbs, or occasionally shrubs, consisting of approximately 950 genera and 20,000 species with worldwide distribution, mostly in the temperate zone. Leaves are simple, often with deeply cut margins and sometimes strong aroma when crushed. Leaf arrangement is alternate or opposite, or occasionally whorled. Flowers are 5¬merous and borne in an involucrate head (capitula), which is borne solitary or in spikes, racemes, cymes, corymbs or panicles. The involucral bracts appear in one to several rows surrounding the head. These may be green and leaf-like, armed with a terminal spine or they may be petal-like. True flowers are small, unisexual or perfect with either the corolla having regular symmetry and 5 (rarely 4) lobes (the disk flowers), or flowers have irregular symmetry with a much enlarged lip (the ligulate or ray flowers). The ovary is inferior with the calyx much modified and sometimes producing bristles called the pappus. Subtending the individual florets on the receptacle surface are sometimes scale-like structures referred to as chaff. Five united anthers surround the terminally forked style. Head colors are in all shades, but yellow and purple predominate. Blooms are mostly produced in the summer and fall. The fruit is a single seeded, woody achene.
- heads (even though not all species have solitary daisy heads)
- united anthers surrounding the 2-branched style
- the achene
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The most characteristic features of the family are:
Plants in this family are easily grown, in fact many species are important weeds. They are best grown in sunny, well-drained sites. Propagation is primarily by seeds, cuttings or division with seeds germinating best with warm temperatures above 70°F. Various pests can affect these plants, but they are not considered especially sensitive to pest problems.
This large family is divided into two subfamlies - the Asteroideae subfamily has at least some tubular florets present in the head while the Lactucoideae subfamily has only ligulate flowers. These subfamlies are divided into a total of 12 tribes to further help define botanical relationships. Important genera belonging to this family include Achillea, Ageratum, Anaphalis, Antennaria, Anthemis, Arctotis, Artemisia, Aster, Bellis, Bidens, Boltonia, Brachycome, Calendula, Cassinia, Catananche, Centaurea, Chrysanthemum, Chrysogonum, Cichorium, Cladanthus, Coreopsis, Cosmos, Cotula, Crepis, Dahlia, Dimorphotheca, Dyssodia, Echinacea, Echinops, Emila, Erigeron, Eupatorium, Gaillardia, Gazania, Gerbera, Haplopappus, Helenium, Helianthus, Helichrysum, Heliopsis, Helipterum, Inula, Krigia, Leontopodium, Liatris, Ligularia, Onopordum, Pachystegia, Parthenium, Ratibida, Rudbeckia, Santolina, Sanvitalia, Senecio, Serratula, Silybum, Solidago, Stokesia, Tagetes, Tanacetum, Tithonia, Townsendia, Ursinia, Vernonia, Xeranthemum and Zinnia.
Typical aster flower in cross section (top); Achene with pappus (center left), Ray or Ligulate flower (center), and a Disk or Tubular flower (center right, much enlarged); Chrysanthemum morifolium (all ligulate flowers, bottom left), Santolina chamaecyparissus (all disk flowers, bottom center) and Helichrysum bracteatum (showy portion is the involcural bracts, bottom right).
Representative Species
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| Achillea filipendulina | Fernleaf Yarrow |
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| * | Achillea millefolium | Common Yarrow |
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| Artemisia spp. | Wormwood |
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| * | Ageratum houstonianum | Ageratum or Flossflower |
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| * | Calendula officinalis | Calendula |
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| Centaurea cyanus | Bachelor’s Button or Corn Flower |
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| * | Coreopsis grandiflora | Coreopsis or Tickseed |
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| * | Cosmos sulphureus | Garden Cosmos or Mexican Aster |
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| * | Cosmos bipinnatus | Orange or Yellow Cosmos |
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| * | Dendranthema x morifolium | Chrysanthemum |
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| Dahlia hybrids | Dahlia |
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| * | Echinaceae purpurea | Purple Coneflower |
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| * | Euryops chrysanthemoides | Daisy Shrub |
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| Farfugium japonicum | Leopard Plant or Ligularia |
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| Gaillardia x grandiflora | Blanket Flower |
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| * | Gazania rigens | Gazania |
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| * | Gerbera jamesonii | Gerbera |
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| * | Helianthus annuus | Sunflower |
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| * | Leucanthemum x superbum | Shasta Daisy |
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| * | Liatris spicata | Gayfeather |
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| Osteospermum x hybrida | South African Daisy or Cape Daisy |
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| * | Rudbeckia hirta | Annual Black-eyed Susan |
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| * | Rudbeckia fulgida | Perennial Black-eyed Susan |
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| * | Senecio cineraria | Dusty Miller |
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| Solidago spp. | Goldenrod |
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| * | Tagetes erecta | African Marigold |
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| * | Tagetes patula | French Marigold |
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| Wedelia trilobata | Wedelia |
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| * | Zinnia elegans | Zinnia |
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