Ageratum houstonianum Mill. var. caeruleum

The wild type is a short-lived perennial, a somewhat untidy plant with blue flowers.  To 60cm.  It is mostly grown as an annual, with most cultivars being compact, mound-forming plants, 15-30cm tall, with numerous small, rounded flower clusters in shades of blue, red and white in summer.  [RHSE, Hortus].

Horticultural & Botanical History

Introduced to Europe in the early nineteenth century.  Johnson’s Dictionary gives a date of 1800 for A. caeruleum and 1822 for A. mexicanumAgeratum mexicanum was raised by Mr. Tate of the Sloane Street nursery from seeds brought from Mexico by Mr. Bullock.  [BM t.2524/1824].  A. mexicanum was recommended as a useful winter greenhouse plant in The Gardeners Chronicle.  [Gard. Chron. 1854]. 

History at Camden Park

Listed in the 1850 and 1857 catalogues [H.3/1850].  Ageratum houstonianum is well established as a weed in parts of Australia and interestingly grows wild throughout the site of John Bidwill’s garden at Tinana.


Ageratum caeruleum Hort. ex Poir. = Ageratum conyzoides L., synonym Eupatorium conyzoides (L.) E.H.L.Krause, a closely related plant.

Published Sep 09, 2009 - 04:53 PM | Last updated Feb 23, 2010 - 01:20 PM

Figured is a spindly shoot topped by an umbel of pale blue flowers.  Curtis's Botanical Magazine t.2524, 1824.

Ageratum houstonianum Mill. var. caeruleum | BM t.2524/1824 | BHL

More details about Ageratum houstonianum Mill. var. caeruleum
Family Asteraceae
Region of origin


  • Ageratum caeruleum Hort.
  • Ageratum conyzoides L. var. houstonianum (Mill.) T.R.Sahu
  • Ageratum mexicanum Sw. 
Common Name

Floss flower, Mexican ageratum, Ageratum

Name in the Camden Park Record

Ageratum caeruleum  

Confidence level high