Harpoonweed

The fully grown A. armata has sparse branches on which long stolons with harpoon-like hooks and erect shoots develop in all directions. The branches, stolons, and shoots ramify over and over again which give A. armata the thallus-like appearance. The ultimate branchlets are filamentous and composed of three cell rows whereas the larger branches consist of a central medullary filament and a gelatinous matrix surrounded by a cortex 3 – 6 cells thick. Gametophytes are terete and are around 200 mm in height. They form dense, pink intertwining clumps. A characteristic feature of this species is barbs, which attach the A. armata to the ocean benthic substrates.

A. armata is a species native to southern Australia and New Zealand (Southern hemisphere) and is thought to have slowly spread to the Northern hemisphere through the Mediterranean sea, as it is highly invasive. It can now also be found along the British Isles to Senegal as well. The first Mediterranean A. armata was reported in Algeria in 1923. When first found, it was considered abnormal to find A. armata in this location due to the high summer seawater surface temperatures along southern Mediterranean coasts. However, it was later found that the particular cool water temperatures that stay below 25 °C would allow the species to survive locally during the summer.

A. armata has a triphasic diplohaplontic heteromorphic life cycle. In this cycle, the three phases include: haploid carposporophyte, gametophyte and diploid zygote. Multiple phases of different morphology and ploidy contribute differently to the expansion potential of A. armata. Gametophytes of this species are microscopic carposoporophytes, which divide into tetrasporophytes that go through meiosis to be developed into the gametophyte. A. armata has two morphologically different stages of development– the gametophyte stage and the tetrasporophyte stage.

A. armata goes through haploid and gametophytic phases in a heteromorphic diplo-haplontic life cycle. The A. armata gametophyte grows into adult form and goes through fecundation to produce diploid carposporophyte; which, then, divide into tetrasporophyte that goes through meiosis to be developed into the gametophyte.