This subgenus consists of minute, slightly elongate bees that have mostly smooth and black or brown integument, sometimes with slightly bluish metallic reflections. Their body length ranges from 3–6 mm (Michener 2007).
(modified from Michener 2007)
Some species of Ceratina (Ceratinula) may be confused with Ceratina (Ceratina), and they have at times been included in the same subgenus (Hirashima 1971a; Michener 1965). Species of C. (Ceratinula) differ from typical species of C. (Ceratina) in their extensive smooth, impunctate areas. They often completely lack punctures on the paraocular area above the antenna and on the genae. C. (Ceratinula) also have forewings with the second submarginal cell narrowed anteriorly, nearly to a point. In addition, their distribution is different; C. (Ceratinula) has a primarily Neotropical distribution, while C. (Ceratina) has an African distribution.
Ceratina (Ceratinula) arizonensis have been observed visiting a number of plant families including: Apiaceae, Asteraceae, Boraginaceae, Epialtidae, Euphorbiaceae, Lamiaceae, Onagraceae, Papaveraceae, Polemoniaceae, Polygonaceae, Rhamnaceae, Scrophulariaceae, Tiliaceae (Daly 1973; Collevatti et al. 1998; Ascher & Pickering 2020).
Michener and Eickwort (1966) described an undeterrmined species of Ceratinula (similar to Ceratina rectangulifera, Schwarz & Michener) nesting in dead stems collected along a shady bank in Costa Rica. The nest was associated with 1 to 5 cells, burrows of about 2.5 mm in diameter, cells between 4 and 5.5 mm in length with partitions as thick as 0.5 to 0.75 mm, and with pollen masses attached to one side of the cell as in other species of Ceratina. Rehan et al. (2015) observed social nesting (in terms of nest reuse) in three Neotropical species of Ceratinula from Panama (C. buscki, C. tricolor and C. zeteki); however, they concluded that because this social behavior was rare, solitary nesting is likely an adaptive trait.
Ceratina (Ceratinula) includes 36 described species, two of which are known to occur in the U.S. (Ascher and Pickering 2020).
Ceratina (Ceratinula) arizonensis has been inadvertently introduced from the North America into Hawaii. It was first reported on Oahu in 1950 and has since established and spread to other Hawaiian islands (Hirashima 1971a).
Ceratinula have a subtropical to tropical distribution in the Western Hemisphere, occurring from the most southern states of the U.S., south through the tropics to Argentina (Michener 2007).