Family: Asteraceae
Scientific Name: Ageratum corymbosum 
Common Name: Ageratum corymbosum, Flattop Ageratum
Pronunciation:
(ad-jur-RAY-tum)(kor-rim-BOW-sum)
plant type:
Annuals
Hardiness zone:
9-10
Sunlight:
sun to part sun
Moisture:
average, tolerates drought once established
Soil & Site:
average
Media:
Temperature:
roots are reported to be hardy to 15 degrees F
Flowers:
6 inch, fluffy violet-blue flower heads borne on branching stalks
Foliage:
starts green and changes to purple
Dimensions:
cam reach 1 foot high by 3 feet spread in warmer climates
Maintenance:
Propagation:
seeds
Origin & History:
Native to northeast Mexico, west Texas and Arizona. (syn Ageratum guatemalense)
Notes & Reference:
I took the pictures of this plant many years ago at a "I can't remember which Botanic garden" Not a lot of info on this plant
Photos: