name of flowering cactus that begins with an "A"?

Answer 1

The following genera of cacti begin their name with letter 'A'

Acanthocalycium
Acanthocereus
Acharagma
Armatocereus
Arrojadoa
Arthrocereus
Astrophytum
Austrocactus
Austrocylindropuntia
Aztekium

The following is the list from other source-

Acanthocalycium Backeb.
Acanthocephala Backeb. = Parodia Speg.
Acanthocereus (Engelm. ex A.Berger) Britton & Rose
Acantholobivia Backeb. = Echinopsis Zucc.
Acanthopetalus Y.Ito = Echinopsis Zucc.
Acanthorhipsalis (K.Schum.) Britton & Rose = Lepismium Pfeiff.
Acanthorhipsalis Kimnach (SUH) = Lepismium Pfeiff.
Airampoa Fric = Opuntia Mill.
Akersia Buining = Cleistocactus Lem.
Ancistrocactus (K.Schum.) Britton & Rose = Sclerocactus Britton & Rose
Andenea Fric (SUI) = Echinopsis Zucc.
Anhalonium Lem. = Ariocarpus Scheidw.
Anisocereus Backeb. = Escontria Rose
Aporocactus Lem. = Disocactus Lindl.
Aporocereus Fric & Kreuz. (SUO) = Disocactus Lindl.
Arequipa Britton & Rose = Oreocereus (A.Berger) Riccob.
Arequipiopsis Kreuz. & Buining = Oreocereus (A.Berger) Riccob.
Ariocarpus Scheidw.
Armatocereus Backeb.
Arrojadoa Britton & Rose
Arthrocereus A.Berger & F.M.Knuth
Astrophyton Lawr. (SUO) = Astrophytum Lem.
Astrophytum Lem.
Aulacothele Monv. (SUI) = Coryphantha (Engelm.) Lem.
Aureilobivia Fric (SUI) = Echinopsis Zucc.
Austrocactus Britton & Rose
Austrocephalocereus Backeb. = Micranthocereus Backeb.
Austrocylindropuntia Backeb. = Opuntia Mill.
Aylostera Speg. = Rebutia K.Schum.
Aztekium Boed.
Azureocereus Akers & H.Johnson = Browningia Britton & Rose

Answer 2

Austrocephalocereus