Key to the species groups of Microphorella in the Nearctic Region

1 Wing with R 1 vein short, terminating at or before midpoint of wing (Fig. 3); female syntergite 9+10 with acanthophorous setae (Figs 16, 17, 31, 32); male terminalia with right epandrial lamella greatly enlarged and comprising most of hypopygium in right lateral view (Figs 4, 11, 20), hypandrium reduced to narrow subtriangular band, only visible from left side of hypopygium (Figs 10, 19)...................................................................... M. breviradia species group

- Wing with R 1 vein long, terminating beyond midpoint of wing (Figs 25, 27); female syntergite 9+10 with acanthophorous spines (Figs 33, 34); male terminalia with right epandrial lamella smaller than hypandrium in right lateral view, hypandrium large and reniform, visible from both left and right side of hypopygium (Figs 26, 28, 30)............................ 2

2 Wing with vein CuA + CuP absent; male wing with long apicoventral seta on hind margin (Fig. 25); male fore tibia and tarsomere 1 with row of posterior comb-like setae; male mid trochanter and mid femur each with strong basiventral seta; hypopygium with elongate medial hypandrial projection and dorsal surstylar lobe with strong sickle-shaped seta (Fig. 26); female abdominal tergite 5 medially with some slender submarginal setae, tergite 6 mainly glaborous... M. chillcotti species group

- Wing with vein CuA + CuP extending slightly beyond cell cua, sometimes faint (Fig. 27); male wing without long apicoventral seta on hind margin; male fore tibia and tarsomere 1 without comb-like setae; male mid trochanter and mid femur each without strong basiventral seta; hypopygium without elongate medial hypandrial projection and dorsal surstylar lobe without strong sickle-shaped seta (Figs 28, 30); female abdominal tergite 5 or 6 usually with either stout median or stout marginal setae (Figs 34, 36)............................................................................................. 3

3 Male hind trochanter with spine-bearing tubercle (Fig. 29); male terminalia with bare hypandrium (Fig. 28); female abdominal tergite 5 usually with cluster of stout median setae (Figs 35, 36), female abdominal tergite 6 without row of stout marginal setae......................................................................... M. acroptera species group

- Male hind trochanter without spine-bearing tubercle; male terminalia with setose hypandrium (Fig. 30); female abdominal tergite 5 without cluster of stout median setae, female abdominal tergite 6 usually with row of stout marginal setae (Figs 33, 34).............................................................................. M. chiragra species group