structural:expansion, stylistic:tone
Subspecies

There are about 30 subspecies in five to eight groups. These can be identified by the male plumage, namely presence or absence of a white neck-ring and/or a white superciliary stripe, the colour of the uppertail (rump) and wing coverts, and the colour of crown, chest, upper back, and flank feathers. As noted above, introduced populations have mixed the alleles of various races by various amounts, differing according to the original stock used for introductions and what natural selection according to climate and habitat has made of that.

An investigation into the genetic relationships of subspecies revealed that the earliest subspecies is likely to have been elegans, suggesting that the common pheasant originated from the forests of southeastern China. Initial divergence is thought to have occurred around 3.4 Mya. The lack of agreement between morphology-based subspecies delimitation and their genetic relationships is thought to be attributed to past isolation followed by more recent population mixing as the pheasant has expanded its range across the western Palaearctic.

Sometimes this species is split into the Central Asian common and the East Asian ring-necked pheasants, roughly separated by the arid and high mountainous regions of Turkestan. However, while the western and eastern populations probably were entirely separate during the Zyryanka glaciation when deserts were more extensive, this separation was not long enough for actual speciation to occur. Today, the largest variety of colour patterns is found where the western and eastern populations mix, as is to be expected. Females usually cannot be identified even to subspecies group with certainty.

Many subspecies are in danger of disappearing due to hybridisation with introduced birds. The last indigenous black-necked pheasant (P. c. colchicus) population in Europe survives in Greece in the delta of the river Nestos, where in 2012 the population was estimated 100–250 individuals.

The subspecies groups, going from west to east, and some notable subspecies are:

Within a maximum clade credibility mDNA gene tree, the most basal group is the elegans -group of the Eastern Clade, diverging from the green pheasant during the Calabrian, and diversifying in Middle Pleistocene around 0.7 million years ago, with the groups of the Western Clade splitting off from those of the Eastern Clade about 0.59 million years ago. While the subspecies of the Western Clade are well geographically separated from each other, the subspecies of the Eastern Clade often show clinal variation and large areas of intergradation. For example, clines connect pallasi-karpowi-torquatus-takatsukasae within the torquatus -group and kiangsuensis-alaschanicus-sohokhotensis-strauchi within the strauchi/vlangalii -group, with the degree of expression of white collar and superciliary stripe in both cases decreasing from north to south. The isolated form hagenbecki is very close to pallasi in phenotype, and has been traditionally treated within the torquatus -group until recently, when it was assigned in one study to the strauchi/vlangalii group. However, the origin of the corresponding feather samples as listed in GenBank is far away from the known distribution of subspecies hagenbecki, and the issue needs further clarification.