Asteraceae - Aster or Composite Family
Contents English Names Index
 
The Asteraceae are the largest family of vascular plants on the earth with over 1000 genera and 20,000 species worldwide. There are 2500 species alone in North America.
The family is easily recognized by clusters of flowers sitting on a head or receptacle. What appears to be a single flower is actually clusters of many small flowers, called ray flowers and disk flowers. The disk flowers grow in the center and the ray flowers around the outside. Some species like chicory and dandelions have only ray flowers, thistles have only disk flowers and species like sunflowers have both types. The lobes of the ray flowers are longer, expanded to resemble a single petal, and are called rays. The receptacle is covered on the outside with several bracts, together forming an involucre.
A tuft of fine hairs or bristles, called pappus, often grows from the top of the fruit. This may enlarge into a plume of hairs to aid in wind dispersal. The fruits themselves are dry and hard, a type known to botanists as achenes.
 
Guide to Identify Groups of Species of the Aster Family
FLOWERHEADS WHITE, WITH RAYS AND DISK FLOWERS
Achillea millefolium - Yarrow
Aromatic perennial, 10-80 cm tall. Plains, slopes, disturbed ground.
Flowerheads white, with 3-5 rays 3-6 mm long, many in flat-topped clusters.
Leaves alternate, fern-like, 2-3 times pinnately divided into fine segments.
Leucanthemum vulgare - Oxeye Daisy
Perennial 20-80 cm tall, stems single, often in colonies. Fields and roadsides.
Flowerheads white, about 5 cm wide, solitary, with 15-30 rays 1-2 cm long.
Leaves alternate, spoon-shaped, mostly hairless, narrowly lobed toothed.
Aster ericoides - Heath Aster
Stems 30-100 cm tall, often clustered. Open, wet or dry places in the valleys.
Flowerheads densely clustered on branches, with 15-25 white rays 3-8 mm long.
Leaves numerous, firm, linear, spine-tipped, 4-7 cm long and 4-5 mm wide.
FLOWERHEADS YELLOW, WITH RAYS AND DISK FLOWERS
Grindelia squarrosa - Curly Gumweed
Aromatic plant, 20-60 cm tall, hairless, with many banches. Dry, open places.
Flowerheads yellow, 2-3 cm wide, with sticky, backward curling involucral bracts.
Leaves alternate, oblong, 10-35 mm long, 6-12 mm wide, with resinous glands.
Helianthus annuus - Common Sunflower
Coarse annual, 40-200 cm tall. Open, dry or moderately moist areas, roadsides.
Flowerheads several, large with yellow rays around a large button of disk flowers.
Leaves alternate, egg- to heart-shaped with rough hairs and long stalks.
Ratibida columnifera - Prairie Coneflower
Stems 30-120 cm tall, usually several from base. Prairies, disturbed ground.
Flowerheads with 3-7 rays, the disc cluster raised to a tall, cylindrical column.
Leaves alternate, lance-shaped, deeply pinnately cut into 5-9 segments.
Senecio triangularis - Arrow-leaved Groundsel
Stems stout, unbranched, leafy, 30-150 cm tall. Moist places, mountains.
Flowerheads in a short cluster, with about 8 yellow rays 7-13 mm long.
Leaves alternate, elongate-triangular, stalked, sharp-toothed, nearly hairless.
Solidago gigantea - Giant Goldenrod
Plant robust, leafy, 30-150 cm tall. Moist, open to shaded places, valleys.
Flowerheads yellow, with 10-17 rays, 1-3 mm long, in dense clusters.
Leaves alternate, crowded, lance-shaped, usually sharply toothed, stalkless.
Arnica chamissonis - Leafy Arnica
Stems single, 20-100 cm tall, softly wavy-hairy. Moist meadows, mountains.
Flowerheads yellow, 3-5 cm across, with 10-16 rays. Bracts hair-tipped.
Leaves opposite, lance-shaped, hairy, in 5-10 pairs, clasping stem, short-hairy.
FLOWERS BLUE OR PINK, WITH RAYS AND DISK FLOWERS
Aster conspicuus - Showy Aster
Stems stout, unbranched, 30-100 cm tall. Open woods, foothills to montane.
Flowerheads blue-violet, with 12-35 rays, many in clusters. Involucre glandular.
Leaves alternate, firm, sharp-toothed, elliptic, 6-15 cm long and 2-6 cm wide.
Erigeron speciosus - Showy Fleabane
Stems often clustered, leafy, 15-80 cm tall. Open woods, foothills to montane.
Flowerheads blue, purple or pink, with 65-150 slender ray florets 9-18 mm long.
Leaves alternate, lance-shaped, hairless, entire, slightly clasping the stem.

FLOWERHEADS BLUE, WITH RAY FLOWERS ONLY

Lactuca tatarica - Blue Lettuce
Hairless plant, 20-100 cm tall. Meadows, thickets, plains to foothills.
Flowerheads blue, about 2 cm wide, with 18-50 rays, in open clusters.
Leaves alternate, narrowly lance-shaped, entire, the lower leaves with lobes.

FLOWERHEADS YELLOW, WITH RAY FLOWERS ONLY

Lactuca serriola - Prickly Lettuce
30-150 cm tall, hairless, branching at sharp angles. Weed, disturbed areas.
Flowerheads 10-15 mm wide, with 13 to 27 ray florets, in open clusters.
Leaves alternate, pinnately lobed, prickly on the midrib beneath and on edges.
Tragopogon pratensis - Meadow Salsify
Stems 15-80 cm tall, hairless, not thick below the flowerhead. Open places.
Flowerheads yellow, 2-3 cm wide. Bracts narrow, not extending past the rays.
Leaves alternate, grass-like, linear, clasping stem, curved back at tips.
FLOWERHEADS SMALL AND COMPACT, WITH DISK FLOWERS ONLY
Anaphalis margaritacea - Pearly Everlasting
Leafy perennial, 20-60 cm tall. Forest openings, foothills-subalpine.
Flowerheads white, 7-10 mm wide, with papery bracts, in dense clusters.
Leaves alternate, lance-shaped to linear, entire, the edges often rolled under.
Antennaria rosea - Rosy Pussytoes
Mat-forming, slender perennial, 5-40 cm tall. Dry, open areas, plains-montane.
Flowerheads pink or white, 4-7 mm long, 5-10 growing in flat-topped clusters.
Leaves grey-hairy, alternate, few on stem. Basal leaves spoon-shaped.
Artemisia dracunculus - Tarragon
Hairless, 50-150 cm tall, stems several. Open, dry sites, plains-montane.
Flowerheads yellowish, 2-4 mm wide, in narrow, elongated, compound clusters.
Leaves alternate, lance-shaped to linear, 3-8 cm long, 2-10 mm wide, entire.
Artemisia ludoviciana - Western Mugwort
Aromatic plant, 30-100 cm tall, often in colonies. Open places, plains-montane.
Flowerheads yellowish and white-woolly, 3-5 mm wide, in tall, narrow clusters.
Leaves alternate, 3-11 cm long, lance-shaped to linear, toothless, white-woolly.
Tanacetum vulgare - Common Tansy
Plant aromatic, branched, 40-150 cm tall, often in patches. Disturbed areas.
Flowerheads yellow, 5-10 mm wide, with disk flowers only, in large clusters.
Leaves alternate, numerous, fern-like, twice pinnately cut into fine segments.
FLOWERHEADS PURPLE, SPINY, WITH DISK FLOWERS ONLY
Arctium minus - Common Burdock
Stout, coarse, branching biennial, up to 150 cm tall. Disturbed areas.
Flowerheads purple, round, bur-like, with hooks, 15-25 mm wide, clustered.
Leaves large, ovate to heart-shaped with thin, woolly hairs underneath.
Cirsium arvense - Canada Thistle or Creeping Thistle
Perennial, 30-150 cm tall. Stems leafy, branched, not winged. Disturbed areas.
Flowerheads pink to purple, 12-25 mm wide, on branched, spineless stalks.
Leaves alternate, lance-shaped, spiny-toothed, deeply pinnately lobed.
Cirsium vulgare - Bull Thistle
Biennial, 30-150 cm tall. Stems branched, spiny-winged. Disturbed areas.
Flowerheads pink to purple, 3-5 cm wide, on branched, spiny stalks.
Leaves alternate, lance-shaped, hairy, spiny-toothed, deeply pinnately lobed.
FLOWERS PURPLE, LONGER, WITH DISK FLOWERS ONLY
Centaurea maculosa - Spotted Knapweed
Rough-hairy, branched biennials. Noxious weeds in fields and roadsides.
Flowerheads pink-purple, 2-2.5 cm wide, with long disk florets, looking like rays.
Leaves alternate, pinnate with narrow lobes, or the reduced upper ones entire.
Liatris punctata - Blazingstar
Perennial, 10-40 cm tall, hairless with several stems. Dry, open areas, roadsides.
Flowerheads purple, with 4-6 large disk florets, in dense, tall and narrow clusters.
Leaves alternate, numerous, narrow, dotted with tiny pits, rough-hairy on edges.
Below is an alphabetical listing with links to presented species of the Aster family:
   
Scientific Name English Name
 

 

Achillea
Anaphalis
Antennaria
Arctium
Arnica
Artemisia
Aster
Centaurea
Cirsium
Erigeron
Grindelia
Helianthus
Lactuca
Leucanthemum
Liatris
Ratibida
Senecio
Solidago
Tanacetum
Tragopogon
Yarrow
Pearly Everlasting
Pussytoes
Burdock
Arnica
Sagebrush, Wormwood, Tarragon
Aster
Knapweed, Cornflower
Thistle
Fleabane
Gumweed
Sunflower
Lettuce
Daisy
Blazingstar, Gayfeather
Prairie Coneflower
Groundsel
Goldenrod
Tansy
Salsify
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