Cape Sable Whiteweed


The journey of life
From flowers to airborne seeds
With a parachute.

A rare and endangered native species is our topic for this week.  The Cape Sable Whiteweed, Ageratum maritimum, is found in the saline soils of Monroe County, the Keys and nowhere else. A herbaceous perennial that grows from a buried rhizome to a height of 20 inches. Additional rooting occurs at leaf nodes that expand numerous bent stems into a cluster that forms a mat like colony. Opposite leaves are ovate to oblong about ½” in length. Leaf margins are toothed. The leaves are semi-succulent that stores water as a way to survive the sandy saline soils.

At the tip of the stems is a peduncle (flower stalk) that attaches to a cluster of pedicles     (stalks of individual flowers). Pedicles are all joined a single point on the peduncle forming an inflorescence called an umbel. Attached to the pedicles are flower heads made up of pinkish disk florets. There are no ray florets with this species, which is not uncommon with members of the Asteraceae family. There is, however, something different with this plant. There is a whitish bristle like appendage that grows from the tip of disk florets referred to as a pappi. The pappi acts as a parachute for windblown seeds.

In Florida there are three species in the genus Argeratum. Only the maritimum is native. The specimen in the photo is in my garden growing in the sandy saline soils of Fort Myers Beach.


Dorothy Rodwell