1	Calypter margin and hairs dark brown. Eye always bare or with sparse setulae	2
–	Calypter margin and hairs white. Eye almost always setulose dorsomedially	3
2	Fronto-orbital plate and parafacial broad and easily viewed laterally. Gena highest posteriorly. Four ori. Abdomen with light coppery tint. Wing length 2.8–3.6 mm. Basiphallus forming complete ring (Figs 269, 270). Distiphallus broad and stout	M.burgessi (Malloch)
–	Fronto-orbital plate and parafacial narrow, inconspicuous laterally. Gena highest at midpoint. Two ori. Abdomen with green metallic sheen. Wing length 1.9–2.3 mm. Basiphallus U-shaped (Figs 291, 292). Distiphallus thin and gracile	M.minimoides Spencer
3	Gena at its highest near anterior margin of eye (Figs 52, 53). Distiphallus with dark distolateral plate and prominent dorsomedial process	M.buccalis Spencer
–	Gena highest near midpoint of eye. Distiphallus not as above	4
4	Four fronto-orbital setae; anterior 2 pairs (ori) very widely spaced (Fig. 57). Surstylus sometimes with elongate tubercle-like setae (Figs 318, 319). Proepiphallus narrow, straight and V-shaped. Basiphallus open ventrally	M.virens group (5)
–	Usually more than 4 fronto-orbital setae, at least on one side; distance between anterior setae not much larger than distance between any other pair of setae. Tubercle-like setae on surstylus all short. Proepiphallus rounded laterally, upcurved anteriorly and usually with separate halves. Basiphallus sometimes forming a ring	10
5	Head (seen laterally) broadest near middle, i.e., without bulging frons. Fronto-orbital plate relatively narrow, slightly wider behind midpoint. Seen laterally, distiphallus gradually tapering apically and with 1 pair of posteromedial bulges/carinae dorsomedially (Fig. 287)	M.matricarioides Spencer
–	Head (seen laterally) usually broadest dorsally, with fronto-orbital plate bulging anterodorsally. Fronto-orbital plate usually swollen medially and narrowed anteriorly. Distiphallus abruptly widened on basal 1/2 and without clear posteromedial bulge	6
6	Wing length 1.8–2.6 mm. Fronto-orbital plate often 1/3 or 1/4 width of frons (Fig. 56). Distiphallus relatively short and squat	7
–	Wing length 2.5–3.5 mm. Fronto-orbital plate swollen to only 1/4 width of frons (Fig. 54), never 1/3. Distiphallus more elongate	8
7	Fronto-orbital plate (seen dorsally) swollen medially, usually at least 1/3 width of frons (sometimes 1/4 width). Male orbital setulae conspicuously long and bushy compared to setulae on eyes (Fig. 57). Wing length 1.8–2.4 mm. Surstylus narrow and with elongate tubercle-like setae (Figs 318, 319). Mesophallus longer, held slightly away from distiphallus. Distiphallus slender apically (Figs 322, 323)	M.virens (Loew)
–	Fronto-orbital plate swollen to only ¼ width of frons, never 1/3. Male orbital setulae slightly longer than ommatrichia, sometimes barely so, relatively sparse. Wing length 1.8–2.6 mm. Surstylus broader and with only short tubercle-like setae at apex (Fig. 297). Mesophallus slender, held close to distiphallus. Distiphallus bulging laterally along distal surface (Figs 299, 300)	M.splendida Frick
8	Notum and abdomen with green shine that may sometimes also be partially coppery. Distal edge of surstylus ~ 1/3 height of epandrium. Basiphallus overlapping base of distiphallus (Figs 326, 327). Large, dark distoventral plate of distiphallus (viewed laterally) continuing past point of insertion of mesophallus	M.virginiensis Spencer
–	Notum with green to bluish tint. Abdomen green (M.vernoniae bronze-green in IN and blue in MN). Distal edge of surstylus at least 1/2 height of epandrium. Basiphallus separate from distiphallus, if only slightly. Dark distoventral plate of distiphallus (viewed laterally) never continuing past point of insertion of mesophallus	9
9	Orbital setulae much longer than ommatrichia, relatively bushy. Notum with blue tint that may become greenish posteriorly (entirely green in IN). Distiphallus gradually narrowing apically; distal section straight (seen laterally); basal section smooth; with inner spinulose patch. Phallophorus longer than wide (Figs 306, 307)	M.vernoniae Steyskal
–	Orbital setulae short, as long as ommatrichia. Notum with faint green tint. Abdomen shiny green. Distiphallus only wide near base, with remainder long and curved (seen laterally); basal section strongly convoluted; inner spinulose patch strongly reduced to absent. Phallophorus higher than long (Fig. 312)	M.vernoniana Steyskal
10	Large and stout-bodied; wing length 3.0–5.0 mm. Three or 4 ori, rarely 2. Abdomen often with blue metallic shine, at least posteriorly. Distiphallus stout and broad. No space between apex of basiphallus and base of distiphallus	11
–	Smaller and more slender; wing length 2.8–3.4 mm. Two or 3 ori. Abdomen blue, green, or coppery. Distiphallus small and slender. Membranous space between basiphallus and base of distiphallus distinct	12
11	Ocellar tubercle with thin strip of setulae extending to base of postocellar. Eye bare. Three dorsocentral setae. First flagellomere as high as gena. Postpronotum with large orange spots anteriorly and laterally. Presutural scutum with faint, narrow pruinose strips medially. Distiphallus broad and rounded with dorsomedial process; internal surface minutely tuberculate; ventrolateral tubules stout and broadly looped; outer surface not sculptured (Figs 275, 276). Basiphallus broad medially, and thin and ill-defined laterally. Metepiphallus without spines	M.diantherae (Malloch)
–	Setulae restricted to anterior 1/2 of ocellar tubercle. Eye setulose. Two or 3 dorsocentral setae. First flagellomere narrower than gena. Postpronotum without orange spots. Scutum without pruinose strips. Distiphallus longer than wide with stout base and long ventromedial plate; with one pair of spinulose internal structures; ventrolateral tubules nearly indistinct laterally; with sculptured lateral surface (Figs 283, 284). Metepiphallus with spines	M.glyptos sp. nov.
12	Distiphallus separated from basiphallus by much more than height of basiphallus (Figs 257, 258)	M.angelicae (Frost)
–	Distiphallus separated from basiphallus by less than height of basiphallus	13
13	Wing length 2.8–3.4 mm. Mid tibia with 2 posteromedial setae. Apex of distiphallus sharply upturned (Figs 303, 304). Basiphallus forming complete ring	M.subvirens (Malloch)
–	Wing length 2.1–2.8 mm, sometimes up to 3.1 mm. Mid tibia with 1 or 2 posteromedial setae. Distiphallus not upcurved apically. Basiphallus U-shaped	14
14	Surstylus relatively small and angled with posterior corner slightly produced. Ventromedial tubules on distiphallus shallowly to strongly looping below main body of distiphallus (Figs 293, 294). Distiphallus separated from phallophorus by height of basiphallus; sides of distiphallus flared outwards towards apex when viewed ventrally, and gradually narrowed apically when viewed laterally. Distal margin of ejaculatory apodeme pointed	M.rutella sp. nov.
–	Surstylus more robust with distal margin broad and straight with posterior corner shallow. Ventromedial tubules on distiphallus held closely against distiphallus. Distiphallus separated from phallophorus by nearly 2 × height of basiphallus; abruptly narrowed on distal 1/2 (seen laterally); shape gently tapering (viewed ventrally). Distal margin of ejaculatory apodeme rounded	15
15	Wing length 2.6–2.7 mm. Ocellar triangle nearly reaching lunule or ending at medial ori. Eye height divided by gena height 5.3. Notum and abdomen faintly greenish. Mid tibia with 1 medial seta. Epandrium deeper dorsally (Fig. 277). Distiphallus (viewed laterally) with strong medial bulge before a strong apical constriction (Fig. 279)	M.eoflacensis sp. nov.
–	Wing length 2.6–3.0 mm. Fronto-orbital plate ending at anterior ors or posterior ori. Eye height divided by gena height 3.8–4.8. Notum more evenly and strongly greenish, and abdomen with very strong green shine. Mid tibia with 1 long and 1 shorter medial seta. Epandrium shallower dorsally (Fig. 261). Distiphallus (viewed laterally) more broadly bulging medially and very gently sloping to apex, not sharply constricted (Fig. 263)	M.brunkei sp. nov.