blanketweed Syllabification: (blan·ket·weed)Pronunciation: /ˈblaNGkitˌwēd/Definition of blanketweed noun a common green freshwater alga that forms long unbranched filaments. It can be a problem in overenriched water and garden ponds. Genus Spirogyra, phylum Chlorophyta, kingdom Plantae (or Protista)