Reprinted with permission from the University of Nebraska State Museum from:
Ribble, D. W. 1968. Revisions of two subgenera of Andrena, Micrandrena Ashmead and Derandrena new subgenus (Hymenoptera: Apoidea). Bulletin of the University of Nebraska State Museum 8: 1-124.
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Andrena viridissima is an isolated species, and also like hermosa, viridissima is most closely related to the vandykei group (the reasons for the subgeneric assignment of hermosa apply equally well here). However, viridissima and hermosa appear less related to each other than each is to the vandykei group. In any case, separate lines of divergence are indicated. About the only characters the two species have in common not shared with the vandykei group are: genal process absent, metallic reflections (these are very weak in hermosa), widened genital capsule and widened sternum eight. Andrena viridissima can be separated from members of the vandykei group by: strong metallic blue-green reflections, groove crossing the posterior pronotal lobe ending in the dorsal margin of the posterior pronotal lobe, humeral angle appears lacking in the female (often very weak in the vandykei group), wide male labrum with a strong labral process, bifurcate male sternum eight (one specimen lacks this bifurcation), male gena elevated near posterior margin and gena lacking a process below the mandible.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 7.1 mm; width of mesothorax, 2.1 mm; wing length from tegula, 5.5 mm; facial length/width, 0.94; foveal length/width, 3.45.
INTEGUMENTAL COLOR. — Body and legs with bright blue-green metallic reflections; clypeus with golden and purple reflections; flagellum orange-brown below; color otherwise as in vandykei.
STRUCTURE. — Head as in vandykei except: scape much longer than flagellar segments 1-4; flagellar segment 1 much longer than 2 and 3 together; mandible and subapical mandibular tooth not sharply pointed; galea with fine reticular shagreening; maxillary palpus with segments in ratio of about 1.3:1.6:1.1:1.4:1.0:1.4; labial palpus with segments in ratio of about 1.7:1.0:1.0:1.3, segment 4 flattened; labral process nearly half as wide and two-thirds as long as entire labrum, expanded at base, apex truncate; clypeus with distinct reticular shagreening over entire surface; supraclypeal area sculptured about like clypeus; genal area in side view as wide as eye; vertex extending past lateral ocellus by less than one ocellar width; facial fovea reaching dorsal margin of eye, dorsally two-thirds width of eye, narrowly rounded below.
Mesosoma as in vandykei except: humeral angle indistinct, suture crossing base of posterior pronotal lobe extending to dorsal margin of lobe; scutellum sculptured like center of mesoscutum; enclosure of propodeum with shagreening not becoming granular towards base; hind tibia slightly widened, nearly twice as wide as basitarsus; serrate part of anterior tibial spur half as long as entire spur; wings with pterostigma large, nearly twice as wide as prestigma; first transverse cubital vein ending about three vein widths from pterostigma.
Metasoma as in vandykei except edges of pygidial plate upturned.
VESTITURE. — Hairs as in vandykei except: hairs of middle leg and hind tarsus white; center of tergum 1 and to some extent tergum 2 with long hairs; apical abdominal fasciae on terga 2-4, interrupted medially on 2 and 3, complete on 4.
MALE. MEASUREMENTS AND RATIOS. — Length, 6.2 mm; width of mesothorax, 1.4 mm; wing length from tegula, 4.6 mm; facial length/width, 0.90; flagellar segment 1/segment 2, 1.75.
INTEGUMENTAL COLOR. — Body and legs with bright blue-green metallic reflections; clypeus yellow except extreme basally and laterally, with lateral hyaline spot on each side; flagellum orange-brown below; color otherwise as in vandykei.
STRUCTURE. — Head as in vandykei except: scape much shorter than flagellar segments 1-3; segment 1 one and three-fourths times as long as 2, one and one-fourth times as long as 3; segment 2 slightly tapered towards base; eye about three and one-half times as long as broad in anterior view, inner eye margins slightly convergent below; mandible and subapical mandibular tooth less pointed than in vandykei; maxillary palpus with segments in ratio of about 1.1:1.3:1.1:1.1:1.0:1.4; labial palpus with segments in ratio of about 1.4:1.0:1.2:1.8; labrum two and two-thirds as wide as long, rounded laterally, process protruding much above surface of labrum, reniform in anterior view when labrum is extended forward; clypeus twice as broad as long, protruding beyond lower margin of eye by half width of eye in lateral view, entire clypeus with weak reticular shagreening, punctures moderate in size, weak, far apart, becoming closer and more distinct laterally; genal area slightly wider than eye, posteriorly coming to broadly rounded angle, just anterior to angle surface elevated, no process below mandible; vertex moderately elevated along posterior margin behind ocelli, but elevated more abruptly than in vandykei, vertex extending past lateral ocellus by one ocellar distance; face above antennal fossae with some fine, irregular rugae.
Mesosoma as in vandykei except: pronotum with suture extending vertically from leg base extending across posterior lobe ending in dorsal margin behind humeral angle.
Metasoma as in vandykei except sternum 6 emarginate.
Sternum 7 emarginate at apex, producing two rounded lobes, each lobe bearing several, mostly branched setae, sternum unshagreened (fig. 118). Sternum 8 with apical half convex, base expanded into large, broad plate (fig. 119); apex much expanded, bifurcate; shaft short, bent downward and then posteriorly; sternum with apical half setose, setae branched, few setae reaching slightly beyond apex. Gonocoxite broad, bent downward; gonoforceps expanded near middle, dorsal surface with several weakly branched setae; dorsal lobes wide, long. Penis valve bent downward, apex moderate in width, rounded in side view, moderately expanded medially, dorsal part with basal lamellae (figs. 115-117).
VESTITURE. — Hairs as in vandykei except: chocolate brown hairs on head and thorax less conspicuous; apical abdominal fasciae weak, absent on tergum 1.
VARIATION. — A few males are much larger (up to 5.5 mm, wing length from tegula) than the allotype. These larger males were collected with specimens of more normal size. The large specimens are more hairy than the allotype (this is especially noticeable on the sterna). One large specimen is very hairy, has a small yellow maculation on each parocular area and lacks the hyaline spots on the clypeus. Some other specimens have the yellow maculation on the parocular areas, sometimes this maculation is only on one side of the face. Often the yellow clypeal maculation is reduced above the hyaline spot and at times the spot and the dark clypeal base are confluent. The male from Baja California, normal in other respects, has the apex of sternum eight emarginate rather than bifurcate.