Aronia was originally put in the genus Pyrus. There is no official name, but some are using Photinia instead of Aronia. It is based on the publication Robertson, K.R., J.B. Phipps, J.R. Rohrer, and P.G. Smith. 1991. A synopsis of genera in Maloideae (Rosaceae). Systematic Botany 16: 376Â394.

According to one website:

Robertson et al. (1991) examined the Maloideae on a world-wide basis and revised generic classification. They found that North American chokeberries (Aronia) possessed similar floral and fruiting morphology to Photinia, previously considered to be a primarily Asian genus. The presence of dark glands along the midrib has been used as a defining character for the genus Aronia. These structures, however, are also found in Photinia, as well as Malus, Pyrus, and other genera (i.e., they do not uniquely define any genus).

What I find odd is that Robertson has a list of recommended shrubs on his website where he includes Black chokeberry, which he calls Aronia melanocarpa! He seems to be an expert on the Rose family though.

I guess that genetic data will proof Aronia to be part of Sorbus. Photinia I don't know enough.