Asterids: Asteraceae

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