BOT 360F - Families of Vascular Plants
ASTERACEAE (Cardueae) - Carduus nutans, Cirsium muticum, Arctium minus (Hill) Bernh. Heads are discoid, and homogamous (or there may be sterile outer florets). Spiny involucral bracts may deter herbivory, and can result in the entire capitulum (containing fruits on which pappus development may be minimal) being dispersed as a single unit (note the hooked spines on the tips of the involucral bracts of burdock, A. minus). Alternatively, the abundant growth of pappus hairs ("thistledown") results in dispersal of individual fruits on wind currents. Globe artichoke (Cynara scolymus) also belongs to this tribe.
Arctium minus (Hill) Bernh. (21603 bytes)
Arctium minus (burdock). 

Photo: R. Presgrave 1997 Royal Ontario Museum (TRT 3480)

Carduus nutans (nodding thistle). 

Photo: R. Presgrave 2004 Royal Ontario Museum (TRT 3480)

Cirsium muticum (swamp thistle). 

Photo: R. Presgrave 2004 Royal Ontario Museum (TRT 3480)

More images of Carduus nutans and Cirsium vulgare can be found HERE, including ones that show pollen grains on the stigmas in great detail (Brian Johnston MICscape article).  

Cynara scolymus, the globe artichoke, produces massive capitula. When blanched, the soft bases of the involucral bracts, as well as (after scraping away the immature flowers) the common receptacle, can be eaten (above).

Photos: (above) © 2005 T. A. Dickinson; (right) Gerald D. Carr, Botany Department, University of Hawaii


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