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Asterids:
Asteraceae
Asterids
• Very large, diverse group
• 10 orders, many families
• Apomorphies:– iridoid compounds– sympetalous corolla– ovules: one integument and the
megasporangium is generally one cell thick
Asteraceae• Probably the most evolved of the families• Two types of flowers
– Ray– Disk
• Herbs in our area, but can be trees in tropics• Very diverse: 19,000 species world-wide• Many flowers on the head inflorescence• Old name is compositae – b/c a composite
of flowers
Asteraceae
•Inflorescence a head (capitulum): (usu.) many flowers arising from a compound receptacle, subtended by inflorescence bracts: involucral bracts or phyllaries, collectively termed the involucre.
• Calyx modified as pappus.
• Fruit an achene.
Floral Formula
Asteraceae – World-wide
Typical Asteraceae Flower
ligulate / ray disk
Cross-section of Asteraceae Flower
More detail on disk flower
Note the chaff – bracts below each individual flower
Fruits are achenes
Sunflower “seeds” = achenes
Echinacea sp. – praire cone flower
Liatris flowers
Close-up of achene fruit with pappus
Taraxacum officinale
Close-up of Taraxacum head
Taraxacum fruits
Close-up of Taraxacum flower
Five types of heads:
1) discoid, with only disk flowers;
2) disciform, with central disk flowers and marginal, eligulate female flowers;
3) radiate, with central (bisexual or male) disk flowers and peripheral (female or sterile) ray flowers;
4) ligulate, with all ray flowers (typically with 5-toothed corolla apices);
5) bilabiate, with all bilabiate flowers.
Bilabiate flower
Acourtia microcephala Trixis californica
posterior lip anterior lip
Ray flowers (heads ligulate = all rays)
Rafinesquia neomexicana Malacothrix californica
ligulate corolla
Disk flower: heads discoid
Palafoxia arida Psathyrotes ramosissima
disk corolla
Chaenactis gabriuscula
Disk flowers: heads disciform(2 types of disk fls.,
same or different heads)
male heads
Ambrosia chamissonis
female heads
Xylorhiza orcuttii Encelia farinosa
Heads radiate: inner disk & outer ray fls.
ray flowers disk flowers
Encelia californica
ovary
Some heads are "chaffy"
chaff : bracts subtending flowers
disk flower
Involucre morphology
one whorl two whorls many whorls
Senecio vulgaris Coreopsis maritima Encelia californica
Circium vulgare Silybum marianum
Phyllaries spiny
Involucre morphology
Phyllaries spiny & squarrose
Pappus: modified calyx
Pappus: modified calyx
capillary bristles: barbellate
capillary bristles: plumose
beak
capillary bristles, borne atop "beak"
Asteraceae
• Because the family is so large, it is divided into two Subfamilies which are then divided into tribes: 12 to 17 in the whole family
• Aster = Subfamily Asteroideae– Six tribes we’ll see
• Dandelion = Subfamily Cichorioideae– One tribe
Tribes of the Aster Subfamily
• Heliantheae
• Asterae
• Anthemideae
• Senecioneae
• Gnaphalieae
• Eupatorieae
• Cynareae
Tribe Heliantheae – Sunflower tribe
• Opposite leaves
• Very resinous
• Bracts attached to individual flowers (chaffy receptacle)
• Both types of flowers
• Sunflower (Helianthus) and Echinacea
Heliantheae
Tribe Asterae – Aster Tribe
• No bracts at the bottom of individual flowers
• Example is genus Aster, generally fewer than 20 “petals” or ligulate flowers
• Similar to above tribe, but without resinChrysothamnus (Rabbitbrush or chico)
• Another important genus is Erigeron aka fleabane daisy
Chyrsothamnus sp. rabbitbrush
Erigeron elatior
Tribe Anthemideae – Chamomile Tribe
• Multiple layers of phyllaries of different lengths
• Richly aromatic
• Thin, dry, and translucent (i.e. scarious) bracts surrounding the flower base
• Artemisia (sagebrush is in this tribe)
• Achillea, Chrysanthemum
Involucre morphology
one whorl two whorls many whorls
Senecio vulgaris Coreopsis maritima Encelia californica
Chrysanthemum
Achillea millefolium - yarrow
Tribe Senecioneae – Senecio or Groundsel Tribe
– Silky pappus around each flower
• Pappus is usually pure white and very abundant
• Usually naked receptacle
• Senecio
Senecio triangularis
Tribe Gnaphalieae – Everlasting Tribe
• Also has scarious bracts around flower base
• No ligulate flowers, only tubular flowers
• Example is cudweed or everlasting (Gnaphalium)
Pussytoes in Gnaphalieae
Tribe Eupatorieae – Boneset Tribe
• “Baseball bat stigmas”
• No ligulate flowers
• Usually naked receptacle
• Snakeweed, Gutierrezia
• Liatris, common ornamental
Gutierrezia sarothrae – broom snakeweed
Liatris punctata
Dandelion Subfamily - Cichorioideae
• The Dandelion Subfamily
• Strap shaped ligulate “petals”
• No tubular flowers
• Dandelions (Taraxacum)
• Lettuce (Lactuca)
• Includes Cardueae Tribe
Lactuca serriola – prickly lettuce
Tribe Cynareae or Cardueae (in your book) – Artichoke Tribe
• Head inside a cluster of tightly compressed bracts• Like an artichoke, which is in this tribe, we eat the
bracts!• No ligulate flowers• Many bristles on receptacle (spines inside
artichoke)• Many thistles are in this tribe, Cirsium and also
knapweeds, Centaurea• Cynara is artichoke• Name for genus Carduus
Artichoke - Cynara scolymus
Cirsium scariosum
Cirsium arvense
Argyroxiphium sandwicense, Silversword endemic toMaui
Argyroxiphium sandwicense, Silversword
Maui