(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna Bidentiseta Branchitergaliae
Heptagennota Pentamerotarsata Radulapalpata 
- Stenonema/fg1)

Nomen hierarchicum: Stenonema/fg1 [f:2004; g:1933] (incl. Stenacron, Macdunnoa

In circumscription fits:

— grex subgenn. Stenonema: Kluge 1988: 287

— gen. Stenonema Traver 1933: 173

— Stenonema/fg1: Kluge 2004: 173

References. Traver 1933: *; – Needham & Traver & Hsu 1935: *; – Spieth 1947: *; – Lewis 1974: ; – Tshernova 1976: *; – Kluge 1988: *; – 1993: *; – 2004: * * * *.

Autapomorphies of Stenonema/fg1.

(1) Superlingua [curved laterally – see Heptagenia/f5=g4 (1)] is especially sharply curved and stretched laterally; by its form differs from any other taxon among Heptagenia/f5=g4 (Kluge 1988: Fig.16).

(2) On tergalii I–VI costal rib is lost, and anal rib [initially situated on anal margin – see Branchitergaliae (3)] is situated at a distance from anal margin, being especially long and nearly straight (Kluge 2004: Fig.56:O). Unique apomorphy.

(3) Tergalii VII are vestigial, lack fibrillose ventral lobe, thus fibrillose lobe [see Branchitergaliae (3)] is present on tergalii I–VI only. Non-unique apomorphy (see Index of characters [1.3.59]); among Heptagenia/f5=g4 fibrillose lobe of tergalius VII is lost also in Kageronia and majority of Ecdyonurus/fg1.

Characters of Stenonema/fg1 of unclear phylogenetic status.

(4) Glossae [initially pyramidal – see Radulapalpata (1)] with straight or slightly curved inner margin, with distal half flattened, as dorsal edge is approximated to median edge (Kluge 2004: Fig.56:I-J,N). The same in Heptagenia/f8=g7; probably, synapomorphy.

Variable characters of Stenonema/fg1. In selected species of Stenacron and Stenonema/fg3 in imago and subimago on fore tarsus 1st segment can be shortened (like in Heptagenia/f8=g7) or not shortened.

Size. Fore wing length 6–16 mm.

Distribution. North and Central America (dominate in Eastern Nearctic).

The taxon Stenonema/fg1 is divided into:

1. Stenacron

2. Macdunnoa

3. Stenonema/fg2

3.1. Stenonema/fg3

3.2. Maccaffertium