"Robust, branching herb to 4 m high, sometimes woody at base, hirsute to subglabrous. Leaves alternate, narrowly linear to subovate, 1–15 cm long, attenuate, cuneate at base; subsessile or with petiole to 2 cm long." (Flora of Australia)

"Capsule terete, 2–4.5 cm long" (Flora of Australia)

We have looked at Ludwigia octovalis after enquiries for seed appeared. The taxon is widespread in Queensland. Difficulty arises because of its similarity with the weedy exotics, Ludwigia peruviana and Ludwigia longifolia. Herbaria for the earlier species in Queensland are restricted to near Brisbane while latter species in Queensland are currently restricted in range to a few sites near Brisbane, the Gold Coast and Cairns. However, it is possible the weedy species may now be present further afield. Capsule differences should be helpful. L. peruviana is described as, "Capsule sharply 4-angled, 1–2 cm long" (Flora of Australia). As shown above, the capsule for L. octovalis is terete and 2-4.5cm long. A treatment for L. longifolia is not yet available.

https://profiles.ala.org.au/opus/foa/profile/Ludwigia%20octovalvis

https://profiles.ala.org.au/opus/foa/profile/Ludwigia%20peruviana

https://bie.ala.org.au/species/https://id.biodiversity.org.au/node/apni/2910049#overview

https://keyserver.lucidcentral.org/key-server/data/08050103-0a0e-4e01-8a03-040d0c020e0a/media/Html/Ludwigia_octovalvis.htm