Australian Fritillary (Argynnis hyperbius ssp. inconstans)
The Australian- or laced Fritillary was described in 1873, originally as a distinct species, but is now regarded as a subspecies of the Indian Fritillary (Argynnis hyperbius (L.)) (see photo). It is endemic to eastern Australia, where it is restricted to coastal areas of southern Queensland and northern New South Wales.
The species inhabited damp areas where the host plants of its larvae, Banks’ Violet (Viola banksii K. R. Thiele & Prober) and the Arrow-leaved Violet (Viola betonicifolia Sm.), were found growing abundantly.
Most of the sites that this species was known to inhabit, have been destroyed due to human activities, thus the populations broke down and disappeared completely; the very last known specimen was finally caught on April 17th, 2001, the Australian Fritillary is now most likely totally extinct.
 Trevor A. lambkin: Argynnis hyperbius inconsistans Butler, 1873 (Lepidoptera: Nymphalidae: Heliconiinae): a review of its collection history and biology. Australian Entomologist 44(4): 223-268. 2017
Bennett’s Seaweed is probably the first marine algae species that was officially declared extinct.
This very small red alga species was described in 1859, it may probably always only have occurred on two places within the harbor of Sydney at the coast of New South Wales, where it apparently was still quite common at the time when it was discovered.
The extinction of this species was caused by various human activities that led to a pollution of the water with suspended sediments which again were blocking the very fine clathrate branches of the algae, resulting in the inhibition of photosynthesis and causing the dead of the plants.
Pedicellate Broom Spurge (Amperea xiphoclada var. pedicellata)
This variety of the Broom Spurge (Amperea xiphoclada (Sieber ex Spreng.) Druce) is known only from the type material that was collected near Sydney, New South Wales; it differs from the nominate form (see photo below) by the prominently pedicellate female flowers.
Since this form was never found since, it is considered extinct.