The green rosella's underparts, neck and head are yellow, with a red band above the beak and violet-blue cheeks.

Common and widespread across Tasmania, the green rosella is rated as least concern on the International Union for Conservation of Nature (IUCN)'s Red List of Endangered species.

A green rosella specimen was collected in Adventure Bay, Tasmania, by ship's surgeon William Anderson on the third voyage of James Cook between 26 and 30 January 1777.

[3] Anderson collected many bird specimens while tasked as the expedition's naturalist, although he died of tuberculosis in 1778 before the return home.

[2] English naturalist John Latham saw it there and wrote about the green rosella in his 1780s work A General Synopsis of Birds.

It was left to German naturalist Johann Friedrich Gmelin to describe the species, which he did as Psittacus caledonicus in the 13th edition of Systema Naturae in 1788.

[5] In 1820, German naturalist Heinrich Kuhl described a specimen that Robert Brown had collected from northwestern King Island on 23 April 1802 during Matthew Flinders' circumnavigation of Australia, naming it Psittacus brownii in honour of its collector.

[6] He based it on the description of la Perruche à large queue, "the long-tailed parrot" by French naturalist François Levaillant in his 1805 work Histoire Naturelle des Perroquets.

[9] Irish zoologist Nicholas Aylward Vigors established the genus Platycercus in 1825, based on the distinctive architecture of the feathers in the tail and wing, including P. flavigaster and P. brownii within it.

[12] Mathews did feel the King Island form was distinctive, being larger and having more red in the plumage than Tasmanian populations and so described it as P. c. henriettae in 1915.

[15] English zoologist John Gould called it the yellow-bellied parakeet, and early Tasmanian settlers knew it as the hill parrot.

[21] The adult green rosella has a yellow head and underparts with blue cheeks and red band on the forehead and upper lores.

Although possibly locally nomadic in places, the green rosella is sedentary; even birds at higher altitudes do not migrate.

It has become rare on King Island, due to land clearing and possibly competition with the introduced common starling (Sturnus vulgaris) for nesting sites.

[23] These include temperate Southern beech rainforest (where it generally keeps to the canopy), wet and dry sclerophyll forest, woodland, Melaleuca shrubland, coastal heath, dwarf alpine conifer forest, sedgeland, buttongrass moors, tussock grassland, as well as fields, orchards and urban parks and gardens.

[29] The tree chosen is generally a eucalypt such as Tasmanian bluegum, manna gum or mountain ash (E. regnans), or myrtle beech.

[22] They leave the nest four to five weeks after hatching and join up with other young birds in flocks, though rely on their parents for food for another fortnight after fledging.

[28] The green rosella is predominantly herbivorous, with the seeds of grasses and trees—especially eucalypts—forming the bulk of its diet; other items eaten include the seed of the soft tree fern (Dicksonia antarctica), cranberry heath (Astroloma humifusum), myrtle beech (Lophozonia cunninghamii), Australian blackwood (Acacia melanoxylon),[28] silver wattle (Acacia dealbata)[31] and buttercups (Ranunculus),[28] berries, nuts and fruit, as well as flowers and new buds of southern sassafras (Atherosperma moschatum), mānuka (Leptospermum scoparium), shining tea-tree (Leptospermum nitidum), swamp honey-myrtle (Melaleuca squamea), Tasmanian bluegum (Eucalyptus globulus), Smithton peppermint (Eucalyptus nitida), messmate stringybark (Eucalyptus obliqua), snow gum (Eucalyptus pauciflora), manna gum (Eucalyptus viminalis), small-fruit hakea (Hakea microcarpa) and native plum (Cenarrhenes nitida).

[24] When feeding, they generally hold food items in their left feet and extract edible parts or break and discard nut shells with their beaks.

[28] Gould noted that early Tasmanian settlers regarded the abundant green rosella highly as food; he agreed that it was very tasty after trying it himself.

[1] The King Island subspecies is listed under the Environment Protection and Biodiversity Conservation Act 1999 as vulnerable,[32] and its population thought to number fewer than 500 birds.

[33] Around 70% of King Island's native vegetation has been cleared, and the remainder is highly fragmented and at risk of too-frequent bushfires.

[36] The species has a reputation for being apathetic and vulnerable to weight gain in captivity; hence it is recommended to be kept in a large aviary of at least 5 m (15 ft) long to keep it active, and to be fed little or no sunflower seeds.