Utricularia adamsii is a floating aquatic bladderwort known from Australia. It was described by Jobson in 2020 and was previous considered a form of U. aurea, although phylogenetic analysis shows a closer relationship with U. muelleri.
U. adamsii is fairly small, especially in comparison to its relative. The stems float in water, with whorls of red or green leaves that reach a diameter of around 4 cm. To support the inflorescence, the species grows an inflated structure that floats on the surface of the water. Each arm of the float comprises a fleshy zigzagging appendage around 3 cm in length, with small branches of leaves sprouting along its length. The flowers are roughly 1cm long and coloured yellow. The upper corolla lip is round, upright and often slightly hooded. The lower corolla lip is rounded and flared forwards, with a prominent bulbous palate region. Red striations are present on the palate and the upper corolla lip. The spur of the flower is longer than the lower corolla lip and thrust forwards under the lip. I observed the spur to have a sparse covering of indumenta.
The species has been recorded in tropical Northern Australia from Darwin to Cape York and is poorly collected, perhaps owing to the inaccessibility of many locations. I observed it twice in the NT, once in the flood plain of the Howard River east of Darwin and again in a shallow watershed near Jabiru in the Kakadu National Park. In Darwin, the plants grew in a seasonally flooded sandplain, which at the time was mostly dry. The plants were growing in a shallow ditch a few centimeters deep, formed by water seeping into a disused trail. In the Kakadu, the plants grew in a shallow grassy creek which again had receeded to a few centimeters in depth. At both locations, the substrate was dark and organic. Sympatric Utricularia included those adapted to wetter environments, such as U. circumvolua, U. involvens, and U. gibba. I observed flowering in the month of May, although the La Nina conditions earlier that year extended the rains.
On Cape York, I observed the species growing at the shallow periphery of a large wetland system within the tropical savannah habitat. The plants were flowering when the water receded to a few centimetres in depth. I was unable to search deeper areas of the lagoon due to an aversion to being eaten by crocodiles.
Utricularia adamsii bears a superficial resemblance to other floating bladderworts, which often have yellow blooms. It could especially be confused with U. gibba, which also has a long spur that is thrust forwards and flowers in receeded watersheds. U. adamsii can be distinguished by its long whorled stems and float structures (compared to simple stolons in U. gibba). A smaller general size and corolla spur longer than the lower corolla lip distinguishes it from U. aurea.
