Crematogaster

Ward, Philip S. & Blaimer, Bonnie B., 2022, Taxonomy in the phylogenomic era: species boundaries and phylogenetic relationships among North American ants of the Crematogaster scutellaris group (Formicidae: Hymenoptera), Zoological Journal of the Linnean Society 194, pp. 893-937 : 903-907

Following Buren (1968), the nominate subgenus of Crematogaster , represented in the Nearctic region by the Crematogaster scutellaris group, is divided by geography into those species occurring in eastern and western North America, here defined arbitrarily as east and west of 102°W longitude. Only two species ( C. cerasi and C. punctulata ) occur in both regions. The last portion of the key (couplets 31–35) covers the six species of Crematogaster (Orthocrema) occurring in the United States and is based on Longino (2003) and Shattuck & Cover (2016). Two other Neotropical species of the subgenus Orthocrema , C. sotobosque Longino, 2003 and C. curvispinosa Mayr, 1862, have been reported from the United States ( Morgan & Mackay, 2017), but we do not consider these records credible.

1. Petiole as wide as, or wider than, long and broadened anteriorly ( Fig. 3A ); postpetiole bilobed, wider than long and with distinct median sulcus; Crematogaster (Crematogaster) .........................................................2

- Petiole rectangular or ovorectangular, longer than wide and not widened anteriorly ( Fig. 3B ); postpetiole subglobular and lacking a distinct median sulcus, except in one species (C. corvina); Crematogaster (Orthocrema) ....................................................................................................................................................31

2. Species occurring in the western United States, west of 102°W .................................................................... 3

- Species occurring east of 102°W in the United States and Canada.............................................................22

3. Mesosoma dorsum densely reticulate-foveolate and opaque, with some overlying rugulae in larger workers; declivitous face of propodeum completely covered with reticulate-foveolate sculpture ( Fig. 4A ); seta-bearing posterolateral extremity of petiole in form of small acute tooth; standing pilosity short and stout, relatively sparse on mesosoma (MSC 4–12), but abundant on gaster (A4SC 48–80) ( Fig. 13A ); relatively small species (HW 0.73–1.02), with broad petiole ( PTW /HW 0.37–0.41) ( Fig. 13C ); Arizona, New Mexico and Mexico........................................................................................................................................................ C. dentinodis

- Mesosoma sculpture variable, but declivitous face of propodeum usually weakly reticulate and sublucid, or smooth and shining ( Fig. 4B ); seta-bearing posterolateral extremity of petiole usually blunter and not in the form of a small acute tooth; standing pilosity almost never in the combination of sparse on the mesosoma and abundant on the gaster, but if this condition applies (see couplet 4 below) then larger, on average (HW 0.96–1.27), with narrow petiole ( PTW /HW 0.32–0.34) ............................................................. 4

4. Mesosoma predominantly reticulate-foveolate and opaque, with overlying rugulae ( Fig. 14C ); promesonotum with short, standing hairs that grade into, and are sometimes difficult to distinguish from, uplifted pubescence (MSC 6–24); gaster with abundant, short, standing pilosity (A4SC 38–70) ( Fig. 14A ); larger species (HW 0.96–1.27) with moderately long scapes (SI 0.74–0.83, SL/HL 0.82–0.92) and propodeal spines (SPL/HW 0.20–0.23) and narrow postpetiole ( PPW /HW 0.27–0.30) ( Fig. 14C ); southern Arizona, Sonora .............................................................................................................................................................. C. vetusta

- Sculpture and pilosity variable but not in the above combination; if standing pilosity abundant on gaster (A4SC> 35) then species smaller, on average (HW 0.71–1.10), and either with more conspicuous mesosomal pilosity (MSC 16–30) and broader postpetiole ( PPW /HW 0.29–0.35) (C. navajoa, C. punctulata ) or mesosoma with reticulate-striate sculpture and scapes shorter (SL/HL 0.73–0.81) ( C. marioni )............ 5

5. Standing pilosity abundant, present on most of the dorsal surface of the mesosoma and gaster (MSC 16–30, A4SC 20–55) ( Figs 5A , 15A ); scape and legs of moderate length relative to mesosoma length (SL/ WL 0.69–0.82, MtFL /WL 0.77–0.85) ................................................................................................................6

- Standing pilosity varying from sparse to common, but not present on the entire dorsal surface of the mesosoma and gaster (MSC 0–15, A4SC 0–38), if present on mesosoma dorsum then usually confined to the pronotal humeri and the mesonotal declivity ( Fig. 5B ); rarely (some workers of C. marioni ) one or two standing hairs on middle of promesonotum but in that case scape and legs short relative to mesosoma length (SL/WL 0.64–0.69, MtFL /WL 0.72–0.76) ..............................................................................................7

20. Upper-third of head predominantly smooth and shiny, with relatively coarse punctures (> 0.01 mm diameter); standing pilosity long and abundant, especially on the gaster (A4SC 14–30) ( Fig. 29A ); longest postpetiolar seta about two-thirds of postpetiole width ( PP-SL / PPW 0.59–0.75) ( Fig. 10A ; see also Fig. 40 ); west Texas, New Mexico, Arizona and adjacent Mexico........................................................... C. browni - Upper-third of head with smaller punctures (<0.01 mm diameter) and often with greater incursion of finely reticulate surface sculpture; standing pilosity shorter and less abundant on gaster (A4SC 4–16) ( Fig. 30A ); longest postpetiolar seta about one-half of postpetiole width or less ( PP-SL / PPW 0.38–0.54) ( Fig. 10B ).....21

21. Standing pilosity present on pronotal humeri and on mesonotal declivity (MSC 6–13) ( Figs 5B , 30A ); scape relatively long (SI 0.82–0.89); propodeal spines short (SPL/HW 0.18–0.22); Colorado and Utah to northern Mexico........................................................................................................................... C. emeryana - Standing pilosity on mesosoma restricted to pronotal humeri (MSC 2–7) ( Fig. 31A ); scapes shorter (SI 0.72–0.81); propodeal spines longer (SPL/HW 0.22–0.25); eastern Canada, south to Florida and west to the Great Plains and Rocky Mountain foothills................................................................................ C. cerasi

22. Promesonotum with distinct rugulose sculpture, imparting a vermiculate (worm-like) appearance ( Fig. 32C ); small species (HW 0.67–0.85), with short scapes and legs (SI 0.72–0.78, MtFL /HW 0.79–0.84) ( Fig. 32B ); propodeal spines short and stout (SPL/WL 0.15–0.19), inwardly curved and directed posterad (SPTD/HW 0.39–0.48) ( Figs 32A, 32C ); swamp-inhabiting species from south-eastern United States.................................................................................................................................................... C. vermiculata - Promesonotum lacking distinct rugulose-vermiculate sculpture; other characters variable ...................23

23. Pronotum with smooth or weakly sculptured median impression, flanked on each side by ruguloreticulate sculpture; in anterior view median impression of pronotum enhancing the distinctness of the median carina of the mesonotum (likened to a gun sight); small, dark-coloured arboreal species (HW 0.88–1.06) with conspicuous standing pilosity on mesosoma and gaster (MSC 12–17, A4SC 20–40) ( Fig. 33A, C ); south-eastern Texas, north-eastern Mexico..................................................................................... C. rifelna - Pronotum without a smooth median depression, flanked by ruguloreticulate sculpture; size, pilosity and nesting habits variable .................................................................................................................................24

24. Propodeal spines short and distinctly incurved (SPL/HW 0.14–0.18; SPTD/HW 0.39–0.47) ( Fig. 6B ); mesosoma smooth to weakly foveolate; standing pilosity relatively sparse on mesosoma and gaster (MSC 2–6, A4SC 5–13); small, arboreal species (HW 0.74–0.92)..........................................................................25 - Either propodeal spines longer and less incurved, or mesosoma more densely sculptured; standing pilosity and size variable..............................................................................................................................26

25. Uniformly dark brown (fresh specimens) ( Fig. 34 ); arboreal species, with variable nesting habits, southeastern United States.................................................................................................................. C. ashmeadi - Bicoloured, gaster black and other body parts ferrugineus-red ( Fig. 35 ); nesting in pine branches and under pine bark in open habitats; Florida and adjacent states ................................................... C. pinicola

26. Standing pilosity conspicuous on head ( Fig. 36B ), with numerous short subdecumbent and suberect hairs (uplifted pubescence), in addition to several pairs of longer setae flanking the midline; standing pilosity also present as numerous fine hairs of varying degrees of inclination and length on mesosoma and gaster (MSC 10–30, A4SC 20–60) ( Fig. 36A ); propodeal spines long (SPL/HW 0.22–0.29) ( Fig. 36C ); south-eastern United States............................................................................................................... C. pilosa - Standing pilosity generally less common and more distinct from the appressed pubescence (at least on the mesosoma and gaster), or present as short bristle-like hairs; propodeal spine length variable........27

27. Propodeal spines long and divergent (SPL/HW 0.26–0.34, usually> 0.27) ( Fig. 37A, C ); dorsal face of propodeum smooth or weakly sculptured; standing pilosity sparse (MSC 0–8, A4SC 11–24) ( Fig. 37A ); marsh-inhabiting species from south-eastern United States, often building carton nests..... C. parapilosa - Propodeal spines shorter (SPL/HW 0.19–0.27); dorsal face of propodeum usually distinctly sculptured; standing pilosity variable; carton nests rarely or never constructed.........................................................28

28. Standing pilosity relatively sparse on mesosoma dorsum, confined to a clump of flexuous setae on the pronotal humeri and occasionally one or two setae on the mesonotal declivity, always lacking on propodeum (MSC 2–14) ( Figs 31A , 38A )......................................................................................................29 - Standing pilosity common and well distributed across the mesosoma dorsum, often including the propodeum (MSC 15–28) ( Figs 5A , 39A ) .....................................................................................................30

29. Side of pronotum and dorsum of promesonotum smooth and shining ( Fig. 38A, C ); midwestern species, occurring from Kansas and Missouri to north-eastern Mexico C. laeviuscula

- Side of pronotum usually distinctly foveolate-striate, dorsum of mesosoma striate ( Fig. 31A, C ); widely distributed, from eastern Canada, south to Florida and west to the Great Plains and Rocky Mountain foothills................................................................................................................................................ C. cerasi

30. Mesosoma dorsum reticulate-foveolate and opaque, lacking striae or rugulae ( Fig. 16C ); propodeal spines directed posteriorly, such that SPTD/HW 0.39–0.46 and SPTD/ PPW 1.11–1.36 ( Fig. 47 ); Great Plains south to northern Mexico, west to Arizona; see remarks under ‘Species accounts’ ................. C. punctulata - Mesosoma dorsum usually with longitudinal rugulae or striae, on a weak reticulate or reticulate-foveolate sublucid background ( Fig. 39C ); propodeal spines directed more posterolaterally such that SPTD/HW 0.46–0.63 and SPTD/ PPW 1.38–1.76 ( Fig. 47 ); eastern Canada to southern United States and west to the Great Plains ................................................................................................................................... C. lineolata

31. Dorsum of head with dilute appressed pubescence and six or fewer standing hairs ( Fig. 11A ................ 32 - Dorsum of head with abundant standing pilosity and no underlying short, appressed pubescence ( Fig. 11B ) ......................................................................................................................................................34

32. Postpetiole bilobed, much wider than long and with a distinct median sulcus; head reticulate-foveolate and opaque ..................................................................................... C. corvina (southern Texas to Honduras) - Postpetiole globular to subquadrate, slightly broader than long, and lacking a distinct median sulcus; head less densely sculptured, mostly smooth and shiny, at least medially ............................................... 33

33. In profile promesonotum usually broadly convex ( Fig. 12A ); anteroventral petiolar tooth relatively well- developed and sharp; gaster with abundant, evenly distributed standing pilosity; southern Texas to Argentina........................................................................................................................................... C. crinosa - In profile promesonotum tending to be somewhat flattened ( Fig. 12B ); anteroventral petiolar tooth usually less well-developed, forming a right or weakly acute angle; standing pilosity moderately common on gaster, denser anterolaterally and often leaving a median strip relatively clear of setae; southern United States to South America ........................................................................................................ C. torosa

34. Standing pilosity on head short and bluntly clavate; body dark brown; Florida and Texas, south to Venezuela....................................................................................................................................... C. obscurata - Standing pilosity on head long and flexuous; body yellow to orange-brown, sometimes with darker head 35

35. Queen small (4–4.8 mm long); worker with short propodeal spines (SPL/HW 0.10–0.19); promesonotum with scattered longitudinal carinulae; mesopleuron predominantly smooth and shiny; eastern United States, west to Texas, south to Costa Rica.............................................................................. C. minutissima - Queen larger (5–6 mm long); where sympatric with C. minutissima in eastern United States, worker with longer propodeal spines (SPL/HW 0.20–0.24), promesonotum tending to have fewer carinulae, mostly on sides, and mesopleuron often reticulate-foveolate and opaque (in allopatry these worker differences do not apply; further study required); eastern United States, west to Utah, Arizona and northern Mexico................................................................................................................................................ C. missouriensis

SPECIES ACCOUNTS

In this section we discuss species for which taxonomic clarification is required, mostly those that were synonymized in Morgan & Mackay (2017) but that are here reinstated. We document differences between these species and their closest relatives and the species with which they were synonymized (usually not the same thing), using quantitative criteria whenever possible. We also discuss a few other taxa, and describe three new species. A full treatment of all species is beyond the scope of this paper, but current understanding of the remaining North American species is captured in the preceding worker-based key.

Figures

Figures 3–12. Crematogaster worker features useful for identification. 3, petiole shape, dorsal view, C. lineolata (CASENT0863235) (3A) and C. torosa (CASENT0795540) (3B); 4, sculpture on declivitous face of propodeum, C. dentinodis (CASENT0863070) (4A) and C. depilis (CASENT0863478) (4B); 5, mesosomal pilosity, C. punctulata (CASENT0863277) (5A) and C.emeryana (CASENT0863099) (5B); 6, position and shape of propodeal spines, dorsal view, C.isolata (CASENT0863072) (6A) and C.pinicola (CASENT0882129) (6B); 7, petiole shape, dorsal view, C.mutans (CASENT0862488); 8, subpetiolar tooth, lateral view, C.mutans (CASENT0862488); 9, promesonotal sculpture, C.californica (CASENT0221085)(9A) and C.coarctata (CASENT0221962) (9B); 10, postpetiolar seta, C. browni (CASENT0863144) (10A) and C. cerasi (CASENT0795541) (10B); 11, cephalic pilosity, C. torosa (CASENT0795540) (11A) and C. missouriensis (CASENT0221041) (11B); 12, mesosomal profile, C. crinosa (CASENT0795543) (12A) and C. torosa (CASENT0863226) (12B).

Figures13–18. Crematogaster workers,showing lateral viewof body (A),full-faceview of head(B) and dorsalview ofbody (C). 13, C. dentinodis (CASENT0102830); 14. C. vetusta holotype (CASENT0863254); 15, C. navajoa worker (CASENT0064826); 16, C. punctulata lectotype (CASENT0923318); 17, C. isolata (CASENT0922731); 18, C. sp. cf. opaca (MCZENT00589113). Images courtesy of AntWeb (www.antweb.org); photographers Jen Fogarty (13), Michele Esposito (14, 16), April Nobile (15), Wade Lee (17), Zachary Griebenow (18).

Figures 19–24. Crematogaster workers, showing lateral view of body (A), full-face view of head (B) and dorsal view of body (C). 19, C. mutans worker (CASENT0922736); 20, C. colei (CASENT0922726); 21, C. detecta holotype (CASENT0863461); 22, C. larreae paratype (CASENT0005943); 23, C. depilis (CASENT0005668); 24, C. californica lectotype (CASENT0923319). Images courtesy of AntWeb (www.antweb.org); photographers Wade Lee (19, 20), Zachary Griebenow (21), April Nobile (22, 23), Michele Esposito (24).

Figures 40–47. Bivariate plots of selected worker measurements in the Crematogaster scutellaris group. 40, PP-SL (postpetiole seta length) by HW (head width) in C. browni (N = 16) and C. cerasi (N = 17); 41, ED (eye diameter) by MtFL (metafemur length) in C. californica (N = 22) and C. coarctata (N = 21); 42, MtFL (metafemur length) by HW (head width) in C. californica (N = 22), C. colei (N = 12) and C. opuntiae (N = 10); 43, MtFL (metafemur length) by HW (head width) in C. depilis (N = 15), C. detecta (N = 11) and C. larreae (N = 5); 44, MtTL (metatibia length) by HW (head width) in C. depilis (N = 15), C. detecta (N = 11) and C. larreae (N = 5); 45, SPL (propodeal spine length) by HW (head width) in workers of C. hespera (N = 18), C. laeviuscula (N = 25) and C. parapilosa (N = 15); 46, SL (scape length) by HW (head width) in C. emeryana (N = 12) and C. marioni (N = 18); 47, SPTD (propodeal spine tip distance) by HW (head width) in C. lineolata (N = 26) and C. punctulata (N = 15).

Figures 25–30. Crematogaster workers, showing lateral view of body (A), full-face view of head (B) and dorsal view of body (C). 25, C. opuntiae (CASENT0922738); 26, C. marioni (CASENT0922734); 27, C. coarctata (CASENT0005667); 28, C. hespera holotype (USNMENT00529501); 29, C. browni (CASENT0922722); 30, C. emeryana (CASENT0922729). Images courtesy of AntWeb (www.antweb.org); photographers Wade Lee (25, 26, 29, 30), April Nobile (27), Michele Esposito (28).

Figures 31–36. Crematogaster workers, showing lateral view of body (A), full-face view of head (B) and dorsal view of body (C). 31, C. cerasi lectotype (USNMENT00529078); 32, C. vermiculata (CASENT0914534); 33, C. rifelna holotype (LACMENT164556);34, C.ashmeadi (CASENT0922720); 35, C.pinicola (CASENT0172943); 36,C.pilosa(CASENT0914530). Images courtesy of AntWeb (www.antweb.org); photographers Michele Esposito (31, 33), Zach (Ziv) Lieberman (32, 36), Wade Lee (34), April Nobile (35).

Figures 37–39. Crematogaster workers, showing lateral view of body (A), full-face view of head (B), and dorsal view of body (C). 37, C.parapilosa holotype (CASENT0863386); 38, C. laeviuscula (CASENT0104828); 39, C.lineolata (CASENT0922733). Images courtesy of AntWeb (www.antweb.org); photographers Zachary Griebenow (37), April Nobile (338), Wade Lee (39).