Aa Baker, 1940 (mollusk)

Aa Reichenbach f., 1854 (orchid)

Aaaaba Bellamy, 2013 (buprestid beetle) When first described in 1864, the genus was named Alcinous, but that proved to be a junior homonym of pycnogonid genus. Charles Bellamy gave it the replacement name Aaaba in 2002, but that name also was already taken by a sponge: Aaaba de Laubenfels, 1936.

Aaadonta Solem, 1976 (endodontoid snail)

Aaages Barovksii, 1926 (coccinellid)

Aaata Semenov, 1906 (buprestid), de Laubenfels, 1930 (sponge)

Cavaticovelia aaa Gagne, 1975 (Hawaiian troglobitic mesoveliid) Described first as Speovelia aaa. Aaa is the Hawaiian word for lava tube. [Gagne & Howarth 1975, Pacific Insects 16(4):399-413]; moved to new genus by Polhemus?

Ada aa (orchid)

Aloe aageodonta Newton, 1993 (African plant)

Quercus aata Muller (Central American oak)

Zyzyxia (H. Robinson) Strother, 1991 (Asteraceae shrub) See also its entry under Interesting Stories.

Zyzza (cicadellid)

Zyzzyva Casey, 1922 (tropical American weevil)

Zyzzyx Pate, 1937 (wasp)

Zyzzyxdonta Solem, 1976 (endodontoid snail) with characters the extreme opposite of Aaadonta.

Zyzzyzus Stechow, 1921 (Coelenterata)

Apolysis zzyzxensis Evenhuis, 1985 (bombyliid fly) Named for the Desert Studies Area on Zzyzx Road, California.

Dikkops (South African burhinid bird) letters in alphabetical order.

Aegilops Hall, 1850 (mollusk; also a grass) The longest word with all its letters in alphabetical order.

chimps, sponge - Common words with letters in alphabetical and reverse-alphabetical order.