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Key to Aphaenogaster species in the southeastern US (from Creighton 1950; Umphrey 1996)
1  

Antennal scape with a conspicuous lobe which extends rearward along the basal fourth or fifth of the scape
...2
  Antennal scape without a basal lobe or, if a small lobe is present, it projects forward and does not involve the basal fifth of the scape
...3
2(1)    Lobe of the scape, seen from the side, flat and thin, its length usually not more than one-fifth the length of the scape
  Lobe of scape, seen from the side, thick, its upper face forming an obtusely projecting angle in the middle, its length usually one-fourth the length of the scape or longer 
3(1)    Basal quarter of the gastric segment with delicate striae which spread fan-wise from the attachment of the postpetiole
  Gaster without basal striae, or if striae are present they do not spread fan-wise and are limited to the basal eighth of the segment
...4
4(3)  Outer face of the frontal lobe bearing a flange which projects rearward in the form of a tooth
  Outer face of the frontal lobe without a toothed flange
...5
5(4)  Postpetiole broader than long and suboval in shape; propodeal spines longer than the dorsal face of the propodeum
  Postpetiole as long as broad or longer than broad, globular or like a truncated cone in shape; propodeal spines, when present, shorter than the dorsal face of the propodeum
...6
6(5) Propodeum unarmed, rounded or angular but without distinct teeth or spines (coastal or sandy areas)
  Propodeum armed with distinct teeth or spines
...7
7(6)  Middle of pronotum with very feeble sculpture, its surface strongly shining; propodeal spines very slender
 

Entire pronotum heavily shagreened or densely sculptured, its surface opaque or subopaque; propodeal spines not notably slender

...8
The remaining species in the fulva-rudis-texana group are difficult to identify to species, with A. fulva generally being the easiest. Many people simply identify them to this group. Some of the information in these couplets is from old sources and the accuracy is, perhaps, questionable. There are some other undescribed forms not included in this key, and not recorded from either AL or MS that are mentioned in Umphrey's paper that could be found in this area, though they are less likely to be.
8(7)      

Anterior edge of the mesonotum rising abruptly above the adjacent portion of the pronotum, the transverse welt thus formed distinctly concave in the middle (as viewed from front to back); propodeal spines at least as long as the declivious face of the propodeum and strongly directed upwards; lateral striations usually present on fore coxae; queens with transverse striae on mesopleura; concolorous reddish brown, including appendages (nest in rotting wood and sometimes soil)
  Anterior edge of mesonotum not abruptly elevated above pronotum, or if slightly elevated, then not concave (as seen front to back); spines typically shorter and directed posteriorly; fore coxae with or without lateral striations; queens lacking transverse striae on mesopleura; color variable
...9
9(8)  Head of the worker, regardless of size, approximately one-third longer than broad; color yellow brown to brown
...10
  Head of the largest workers (mandibles excluded) not more than one-sixth longer than broad; head of the smaller workers approximately one-fifth longer than broad; color light brown to piceous
...11
10(9)   Large workers 5.5 mm in length; female 7 mm in length; color yellow to dark brown; mandibles shinier and smoother (the only reliable records in the Southeast of this species are from Arkansas)
  Large workers 4.5 mm in length; female 5.5 mm in length; color yellow brown to reddish, legs yellowish and shining (including coxae); mandibles with longitudinal carinulae present (common in woods, nests in soil) (can't tell apart A. carolinensis Wheeler from A. N19, a form described by Umphrey (1996). with morphological characters; chromosome work is needed to differentiate these two forms. However since A. N19 has not been described as a true species, I am calling ours A. carolinensis for now ).
11(9)  Eyes with 13-15 facets in greatest diameter (eyes are obviously bigger than eyes of rudis and picea when compared); propodeal spines slightly incurved when seen from above and directed back; dorsum of the propodeum with very coarse, transverse rugules; color light to dark brown or piceous, especially the gaster (found in southern portions of the Coastal Plain and along the Mississippi River in MS and probably LA)
  Eyes with 10-11 facets in greatest diameter; propodeal spines divergent when seen from above; transverse rugae on the dorsum of the propodeum feeble and often replaced by punctures (found in higher elevations, rocky or mountainous habitats)
...12
12(11)

All antennal segments concolorous reddish brown; the area between the eye and the frontal lobe with reticulate rugae that are not obscured by the interrugal sculpture; pronotum often crossed with transverse rugules; color light brown to dark medium brown (lower elevations of eastern mountains)

  The four apical antennal segments reddish brown, contrasting with the dark brownish to blackish color of the remainder of antenna; the area between the eye and frontal lobe densely punctate with the punctures largely obscuring or replacing the rugae; pronotum evenly punctato-granulose, without transverse rugules; coloration dark brown to piceous (mountainous or rocky habitats at higher elevations)