Question: Between Sidalcea and Backhousia, which genus can only be naturally found in Australia?

Context paragraphs:
Sarcosine: Sarcosine, also known as "N"-methylglycine, is an intermediate and byproduct in glycine synthesis and degradation.  Sarcosine is metabolized to glycine by the enzyme sarcosine dehydrogenase, while glycine-"N"-methyl transferase generates sarcosine from glycine.  Sarcosine is an amino acid derivative that is naturally found in muscles and other body tissues.  In the laboratory, it may be synthesized from chloroacetic acid and methylamine.  Sarcosine is found naturally as an intermediate in the metabolism of choline to glycine.  Sarcosine is sweet to the taste and dissolves in water.  It is used in manufacturing biodegradable surfactants and toothpastes as well as in other applications.

Malassezia: Malassezia (formerly known as Pityrosporum) is a genus of fungi.  Malassezia is naturally found on the skin surfaces of many animals, including humans.  In occasional opportunistic infections,

Cladosiphon okamuranus: Cladosiphon okamuranus (mozuku ) is a type of edible seaweed in the genus "Cladosiphon", naturally found in Okinawa, Japan.  Most mozuku is now farmed by locals, and sold to processing factories.  The main use of mozuku is as food, and as a source of one type of sulfated polysaccharide called Fucoidan, which is used as a cancer treatment aid and health supplement.

Backhousia citriodora: Backhousia citriodora (common names lemon myrtle, lemon scented myrtle, lemon scented ironwood) is a flowering plant in the family Myrtaceae, genus "Backhousia".  It is endemic to subtropical rainforests of central and south-eastern Queensland, Australia, with a natural distribution from Mackay to Brisbane.  Other common names are sweet verbena tree, sweet verbena myrtle, lemon scented verbena, and lemon scented backhousia.

Salmo: Salmo is a genus of fish in the salmon family Salmonidae that includes the European species of salmon and trout, among them the familiar Atlantic salmon "Salmo salar" and the brown trout "Salmo trutta".  The natural distribution of "Salmo" also extends to Northern Africa and to Western Asia around the Black Sea basin.  The single "Salmo" species naturally found in the Atlantic North America is the Atlantic salmon, whereas the salmon and trout of the Pacific basin belong to another genus, "Oncorhynchus".  The generic name "Salmo" derives from the Latin "salmō" (salmon).  The number of distinct species and subspecies in "Salmo" is a debated issue.  Atlantic salmon and brown trout are widespread species, while most of the other taxa are narrowly distributed forms endemic to single watersheds.

Backhousia: Backhousia is a genus of thirteen currently known species of flowering plants in the family Myrtaceae.  All the currently known species grow naturally only (endemic) in Australia in the rainforests and seasonally dry forests of Queensland, New South Wales and Western Australia.

Berberis aristata: Berberis aristata, also known as Indian barberry, "chutro" or tree turmeric, is a shrub belonging to the family Berberidaceae and the genus "Berberis".  The genus comprises approximately 450-500 species of deciduous evergreen shrubs and is found in the temperate and sub-tropical regions of Asia, Europe, and America.  "B. aristata" is native to the Himalayas in India and in Nepal.  It is also naturally found in the wet zone of Sri Lanka.

Phaleria octandra: Phaleria octandra is a shrub found in tropical Australia.  It is also naturally found in the New Guinea, Indonesia, Malaysia and the Solomon Islands.

Typhlops vermicularis: Typhlops vermicularis, the European blind snake or European worm snake, is a species of snake in the genus "Typhlops."  Despite its common name, the range of the European blind snake ranges from the Balkan Peninsula, the Aegean Islands, and Cyprus to Afghanistan.  The common name refers to how it is the only blindsnake of the genus "Typhlops" naturally found in Europe.  The only other blindsnake found in Europe is the brahminy blindsnake, or "flowerpot snake," "Ramphotyphlops braminus", where specimens have been discovered lurking in the soil at the Kew Gardens.

Sidalcea: Sidalcea is a genus (approx. 25 species) of the botanical family Malvaceae.  It contains several species of flower known generally as checkerblooms or checkermallows, or prairie mallows in the United Kingdom.  They can be annuals or perennials, some rhizomatous.  They are native to West and Central North America.

Supporting paragraphs: Sidalcea Backhousia
Answer: Backhousia