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Alligator Weed

Alternanthera sp. (most likely A. philoxeroides)

Description:

I think this may be Alligator Weed (Alternanthera philoxeroides), an invasive species in the Australian ecosystem. Native to South America. Can be semi-aquatic, aquatic, or terrestrial herbaceous plant that produces roots at its stem joints. Stems are often hollow when growing in water, and form dense mats of vegetation out over the water surface. Its oppositely arranged leaves are almost stalkless and elongated in shape (2-14 cm long and 1-4 cm wide), although they appear to be quite rounded when young.

Habitat:

Spotted at Cormorant Bay at Lake Wivenhoe Dam, to the west of Brisbane. Freshwater lake. Sunny, exposed location, subject to wind and wave action. Surrounding area is dense native bushland.

Notes:

You'll notice in the first image that the new leaves form a small rosette, and this led me to think the spotting was Water Lettuce (Pistia stratiotes) which also occurs in the Brisbane area. https://weeds.brisbane.qld.gov.au/weeds/... However, the leaves on this species are quite thick, have ridges that run from leaf base to tip, and it's a free-floating plant with feathery roots that dangle below the water surface. It doesn't have stems like Alligator Weed. I didn't see much of this weed around the lake's edge, and this cluster was quite small, so most likely quite young. No flowers yet which would have made ID much easier. Leaves will most likely become longer and more pointed as the plant ages.

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Neil Ross
Spotted by
Neil Ross

Caboolture, QLD, Australia

Spotted on Jun 8, 2018
Submitted on Jun 9, 2018

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