16-001014-02A (Ultimate SCMMP)

                                                                  Alligator weed

                                                                  Perennial rhizomatous herb that may grow
                                                                  as a terrestrial, emergent, or free-floating
                                                                  aquatic plant. Large mats of interwoven
                                                                  stems often form along the margins of
                                                                  constructed wetlands and may extend over
                                                                  the water surface.
     Photo: Geoff Sainty
                                                                  Distinguished by hollow stems with opposite
                                                                  leaves. Ball-shaped, white flower heads on
                                                                  stalks to about 9 cm, originating from the
                                                                  leaf-stem nodes.

                                                                  Note: Alligator weed can easily be confused
                                                                  with Ludwigia spp. (water primrose) and
                                                                  Persicaria spp. species (smartweeds).

                                                                  Flowering: December–April but will vary with
                                                                  location in Queensland

                                                                  Reproduction: Viable seed not recorded in
                                                                  Australia. Reproduces vegetatively via stem
                                                                  fragmentation, which can occur:

                                                                  • naturally at the end of the growing season
                                                                    from the feeding habit, and the plant’s
                                                                    reaction to the feeding habit, of the flea
                                                                    beetle Agasicles hygrophila

                                                                  • due to wave action or physical damage by
                                                                    boats and mowers

                                                                  Stem fragmentation can be increased by
                                                                  herbicide use.

                                                                  Control: Physical removal, chemical control,
                                                                  biological control



                                                                  Glush weed (Hygrophila costata)

                                                                  Semi-aquatic perennial herb that grows to 1 m
                                                                  high. May also scramble up through taller
                                                                  vegetation.

                                                                  Distinguished by 4-angled stems, leaves in
                                                                  opposite pairs, and white flowers to 1 cm long
                                                                  that grow in clusters at the leaf-stem junction.

                                                                  Flowering: All year

                                                                  Reproduction: Spreads by seeds and
                                                                  vegetatively by rooting at the nodes and
                                                                  fragments. Can produce roots from severed
                                                                  leaves.
     Photo: Geoff Sainty                                          Control: Physical removal, chemical control




62                         Maintaining Vegetated Stormwater Assets Version 1