Key to Palaearctic Cardiocondyla

Key to the species of Cardiocondyla with outdoor occurrence in the Palaearctic, based on Seifert (2023).

This key almost thoroughly used dichotomous decision schedules for cases requiring combinations of multiple characters and in the same time it aspired to achieve a low error rate inevitably resulting in tedious procedures. Lamenting does not help here and those who think that simple answers can be given for difficult problems bark up the wrong tree. The finally best approach is here using a software providing linear discriminant functions (LDA), measuring the full set of morphometric characters and running the investigated samples as wildcards within the data space of the hypothesis-providing supplementary file SI2. It is convenient to run the analysis with primary (raw) measurements instead with ratios. A good check of the result is then comparing with the images that are given for any species in four aspects and to consider geographic distribution. The low error rates reported in the key cannot be achieved for such tiny ants without high-resolution optical systems, a good measuring stage and a careful realization of character definitions.

1

 * Anterior postpetiolar sternite laterally more prominent than in median part—as result an imagined cross section shows a deeply concave ventral margin of the sternite. The lateral protrusions appear in frontolateral view as dents (Fig. 113). Cardiocondyla wroughtonii group
 * Anterior postpetiolar sternite in median part more prominent or at equal level as the lateral surface—as result an imagined cross section shows a convex or straight ventral margin of the sternite

2

 * With all measurements in mm, discriminant 34.21*CW-59.33*PoOc-177.83*EYE+72.15*SL-113.56*FRS-106.46*SP+140.69*PpW-14.15 < 0 [error 0% in 37 nest sample means of two workers measured]. 1st gaster segment in a majority of samples with absent or weakly developed blackish pigmentation. Worldwide tramp species. Outdoor occurrence confirmed for the Middle East. Figs. 105–108 Cardiocondyla wroughtonii
 * Discriminant > 0 [0% error in 65 nest sample means of two workers]. 1st gaster segment in a majority of samples with strongly developed blackish pigmentation. Worldwide tramp species. Outdoor occurrence confirmed for southern Spain and the Middle East. Figs.109–113 Cardiocondyla obscurior

3

 * True foveolae on vertex dorsal of the eyes completely absent. Instead the bases of pubescence hairs are placed in the center of flat tubercles or flat pits of only 4–10 µm diameter, giving a finely punctate surface appearance at lower magnifications (Figs. 89, 97). Postocular distance large, PoOc/CL 0.416–0.467. Frons usually very wide, FRS/CS > 0.288 (except [[Cardiocondyla tibetana, here 0.280 ± 0.006). Propodeal spines reduced to blunt dents. Metanotal depression deep. Cardiocondyla stambuloffii'' group
 * Bases of pubescence hairs on vertex dorsal of the eyes placed in the center of foveolae or cuticular meshes of > 10 µm diameter (Figs. 9, 25, 117)—if foveolae reduced (Cardiocondyla verdensis), than PoOc/CL < 0.394. Frons narrower, FRS/CS < 0.288. Metanotal depression varying from nearly absent to deep. Propodeal spines variable

4

 * Eye larger, EYE/CS >0.235. Frons narrower, FRS/CS <0.295. Waist segments lower, PeH/CS <0.343, PpH/CS < 0.283. Southern and northern margin of Tarim Basin. Figs. 101–104 Cardiocondyla tibetana
 * EYE/CS <0.235, FRS/CS > 0.295, PeH/CS >0.343, PpH/CS < 0.283

5

 * Posterior 40% of vertex surface completely smooth except for tiny pits of 4–5 µm around the bases of pubescence hairs just visible with high-resolution stereomicroscopy. Pubescence longer. With all measurements in mm, discriminant 334.68*PLg-45.456*CW+88.43*PoOc-66.63*EYE -3.60 > 2.3. South Kazakhstan. Figs. 98–100 Cardiocondyla gibbosa
 * Posterior part of vertex not completely smooth, at least with weak rugulae and small tubercles around the bases of pubescence hairs. Discriminant < 2.3

6

 * Westpalaearctic, known range extending east to the western shores of Caspian Sea. With all measurements in mm, discriminant 44.95*CW+54.68*PoOc+31.14*SL-130.25*SPBA-79.81*PpW +40.84*PeH+90.89*PpH -28.33 < 0.4 [0% error in 82 individuals]. Figs. 86–89 Cardiocondyla stambuloffii
 * Central Palaearctic, known range extending from western coast of Caspian Sea east to Mongolia. Discriminant > 0.4 [0% error in 59 individuals]

7

 * With all measurements in mm, discriminant 120.6*PoOc-29.53*SL+109.54*PeW-109.42*PeH-157.97*PLg-7.70 < 0.7 [0% error in 37 individuals]. Figs. 94–97 Cardiocondyla rolandi
 * Discriminant > 0.7 [0% error in 22 individuals]. Figs. 90–93 Cardiocondyla koshewnikovi

8

 * Propodeal spines reduced to obtusely angled corners (Fig. 115). Postpetiole rather narrow, PpW/CS < 0.46, in dorsal view never suggestively hexagonal. With all measurements in mm, discriminant 48.06*PoOc+27.66*SL-56.96*PpW+119.07*Mgr-13.79 > 0 [error 0% in 17 individuals]
 * Propodeal spines not reduced to obtusely angled corners. If spines occasionally reduced to blunt corners, then EYE/CS > 0.221 and PpW/CS >0.450. Discriminant < 0 [error 0% in 1140 individuals]

9

 * Head elongated CL/CW > 1.16 (Fig. 114). Dorsum of promesonotum and lateral pronotum with more developed microsculpture (Figs. 115, 116). Head sculpture stronger, foveolae with regular margin (Fig. 117). Egypt and Saudi Arabia Cardiocondyla fajumensis
 * Head very short CL/CW < 1.16 (Fig. 114). Dorsum of promesonotum and lateral pronotum nearly glabrous (Figs. 119, 120). Head sculpture weaker, foveolae sometimes with irregular margin (Fig. 121). Iran Cardiocondyla unicalis

10

 * Frons very narrow, FRS/CS 0.196—0.228 (Fig. 122), postpetiole with a bulging sternite and high (Fig.123.), PpH/CS 0.306–0.358. With all measurements in mm, discriminant 128.52*FRS+42.56*PeW-143.94*PpH+1.616 < 0 [error 0% in 145 specimens]. Confirmed outdoor occurrence in S Iberia, N Africa and Middle East. Figs. 122–125 Cardiocondyla emeryi
 * Frons wider and postpetiole without a strongly bulging sternite. Discriminant > 0 [error 0% in 863 specimens]

11

 * Small, CW < 420 mm. Metanotal depression very weak or absent, spines well developed, postpetiole much lower than petiole and with a completely flat sternite (Fig. 127). vertex with deeply impressed foveolae (Fig.126). All surfaces of head, mesosoma and waist matt (Fig. 128). Outdoor occurrence confirmed for Egypt and Saudi Arabia Cardiocondyla minutior, Cardiocondyla tjibodana & Cardiocondyla goa
 * Note: These species are inseparable by single or few characters. It is recommeded to measure CL, CW, SL, EYE, FRS, SP, PpW, PeH, PpH and PLg and then running the test specimens as wild-cards in a LDA against the data given in supplementary information SI2. The total classification error in 210 worker individuals in SI2 is 2.4%. Users who refrain from doing this time consuming and challenging separation are recommended to name this collective cluster the Cardiocondyla minutior aggr.
 * Larger, CW > 420 mm. Minute specimens of Cardiocondyla mauritanica may match the character combination of 11a but differ by shorter spines and a thinner petiolar peduncle (compare Figs. 127 and 130)

12

 * Outlines of postpetiole in dorsal view approximately hexagonal (Fig. 131). Metanotal depression shallow (Mgr/CS 2.14±0.52). Propodeal spines developed as short dents (Fig. 130). gastral pubescence dense (sqPDg 3.72 ± 0.28). Postocular distance large (PoOc/CL 0.447 ± 0.008, Fig. 129). Microsculpture on vertex strongly reticulate (Fig. 132). With Mgr, PoOc and SP in mm and sqPDg in µm, discriminant 136.0*Mgr-25.0*PoOc*73.99*SP+1.81*sqPDg-7.2322 < 0 [error 0% in 151 specimens]. Mediterranean and South Temperate zone of the Palaearctic Cardiocondyla mauritanica
 * Outlines of postpetiole in dorsal view not approximately hexagonal. Metanotal depression usually deeper, propodeal spines more developed, gastral pubescence often more dilute, postocular distance usually smaller. Microsculpture on vertex different. Discriminant > 0 [error 0.3% in 619 specimens]

13

 * Postocular distance extremely small (PoOc/CL <0.340). Petiole height and postpetiole width very low. With all measurements in mm, discriminant 30.96*PoOc-38.98*CL+17.12*PeH+26.77*PpW+ 7.196 <0 [error in 4 specimens 0%]. Kuweit. Figs. 62–65 Cardiocondyla opistopsis
 * Postocular distance larger (PoOc/CL 0.342–0.469]. Petiole height and postpetiole width higher. Discriminant >0 [error 0% in 612 specimens]

14

 * Head surface between inner eye margin and paramedian vertex strongly microrugulose (Fig. 69). Dorsal promesonotum longitudinally microrugulose (Fig. 68). All surfaces of head, mesosoma and petiole matt due to more developed microsculpture. Dorsal profile of mesonotum straight, contrasting the clearly convex dorsal profile of propodeum, metanotal depression feebly suggested (Fig. 67). With all measurements in mm, discriminant 95.88*EYE-164.99*Mgr-12.035 > 0. Yemen. Figs. 66–69 Cardiocondyla rugulosa
 * Body surfaces less microrugulose, often shiny. Dorsal profile of mesosoma different. Discriminant < 0

15

 * Microsculpture of head with irregular foveolar margins (Fig. 73). Additionally differing from members of the elegans and ulianini group by larger eye (EYE/CS 0.265–0.274] and from members of the batesii group by longer tergite pubescence (PLg/CS 6.84–6.94). Afghanistan. Figs. 70–73 Cardiocondyla kushanica
 * Foveolae on vertex not with irregular margins. Character combination different

16

 * Foveolae on vertex extremely small (dFOv 7.0–9.1 µm). Tergite pubescence very dilute (sqPDg 5.88–5.92). Scape and head much elongated (SL/CS 0.854–0.867, CL/CW 1.238–1.256). All body surfaces very shiny. Island endemic of Cape Verde, Figs.82–85 Cardiocondyla verdensis
 * Foveolae much larger (dFOv 12–21 µm). Tergite pubescence often more dense. Scape and head usually shorter

17

 * With sqPDg in µm and all other measurements in mm, discriminant 201.57*PLg-0.32*sqPDg-40.86*CL-10.32*PoOc+70.74 *SL+23.72*SPBA-24.27*SP+26.48*PeW+12.96*PpW-73.42*PeH-8.61 > 0 [error 0% in 177 individuals].Cardiocondyla elegans group
 * Discriminant < 0 [error 0% in 322 individuals]. Cardiocondyla batesii & Cardiocondyla ulianini group

18

 * Occurring from Iberia accross S France to Italy. Contact zone with dalmatica in the border region of NE Italy and Slovenia. With all measurements in mm, discriminant 56.7*SP+156*PeW-61.9*PoOc-126.2*PeH-48.2*PpW+126.6*Mgr+17.86 >0 [error 0% in 81 two-specimen nest samples]. Figs. 6–9 Cardiocondyla elegans
 * Occurring farther east. If found in NE Italy or Slovenia, discriminant < 0

19

 * Combination of larger foveloar diameter on vertex, lower postpetiolar height, longer propodeal spines and higher pubescence distance on gaster tergites. With dFOv, sqPDg in µm and SP, PpH in mm, discriminant 1.623*sqPDg+0.718*dFOv+96.14*SP-62.63*PpH-15.233 > 2 [error 0% in 13 specimens]. S georgia, NE Turkey, Iran, Afghanistan. Figs. 18–21 Cardiocondyla brachyceps
 * Foveolar diameter smaller, postpetiolar height larger, spines shorter, pubescence distance smaller. Discriminant < 2 [error 1.4% in 72 specimens]

20

 * Bases of propodeal spines more approached, petiole narrower and higher, surface of propodeum glabrous, propodeal spines very acute, petiole high with a very steep anterior profile of the node. With all measurements in mm, discriminant 163.8*PeH-29.1*PeW-134.63*SPBA-5.68 >2 [error 0% in 6 specimens]. Asia Minor. Figs. 14–17 Cardiocondyla dalmaticoides
 * Bases of propodeal spines more distant, petiole wider and lower, surface of propodeum less glabrous, propodeal spines less acute, petiole lower with a less steep anterior profile of the node. Discriminant <2 [error 0% in 59 specimens]. From N Italy across the whole Balkans, Cyprus and Asia Minor east to the Iran. Northern range border in Austria, Slovakia and Hungary at 48°N. Figs. 10–13 Cardiocondyla dalmatica

21

 * With all measurements in mm, discriminant 32.44*CW-103.36*CL+134.03*PoOc-44.05*EYE+23.08*SL-41.77*SPBA+48.21*PpW-0.135 < 0 [error 0% in 98 individuals]. Species of the Cardiocondyla batesii group
 * Discriminant > 0 [error 0.4% in 241 individuals]. Species of the Cardiocondyla ulianini group

22

 * Frontal carinae notably diverging frontad, FL/FR >1.109. Postocular distance large, PoOc/CL >0.408. Metanotal depression very shallow, Mgr < 2.5 %. Jordan. Figs. 74–77 Cardiocondyla tenuifrons
 * Frontal carinae less diverging, FL/FR <1.110. Postocular distance smaller, PoOc/CL <0.409. Metanotal depression deeper, Mgr usually > 2.5 %

23

 * Petiole massive, ratio PeW /PpW > 0.57. With all measurements in mm, discriminant 152.578*PeW-69.53*PpW+2.092*SL+30.63*PoOc-10.57 > 2.5 [error 0% in 4 individuals]. Only known from two sites in Asia Minor. Figs. 58–61 Cardiocondyla semirubra
 * Petiole less massive, ratio PeW/PpW in 97% of individuals <0.57. Discriminant < 2.5 [error 0% in 132 individuals. Figs. 54–57

24

 * With all measurements in mm, discriminant 63.22*CL-63.18*PoOc+55.89*SL+64.64*PeW-184.93*PeH-93.82*PpH-11.19 < 0 [error 0% in 37 specimens]. Morocco, Tunisia, Algeria, Spain. Figs. 54–57 Cardiocondyla batesii
 * Discriminant > 0 [error 0% in 95 specimens]. Portugal, Morocco, Algeria, Tunisia, Egypt, Cyprus, Turkey, Middle East, Iran eastwards to 56°E. Color polymorphic. Figs. 78–81 Cardiocondyla nigra

25

 * Frons very narrow, FRS/CS 0.225; propodeal spines acute but very short, SP/CS 0.071; postocular distance small, PoOc/CL 0.403; postpetiole wide PpW/CS 0.552. With all measurements in mm, discriminant 160.18*FRS+41.17*PoOc-45.99*PpW-15.23 <0. Israel. Figs. 34–37 Cardiocondyla gallilaeica
 * Frons wider; propodeal spines longer; postocular distance larger; postpetiole often narrower. Discriminant > 0 [error 0% in 240 specimens]

26

 * Combination of large propodeal spine base distance, small eye, large postocular distance, broad and high postpetiole. With all measurements in mm, discriminant 44.74*PoOc-167.14*EYE+161.96*SPBA-56.07*PpW+31.77*PpH+0.543 >0 [error 0% in 179 specimens]
 * Propodeal spine base distance smaller, eye larger, postocular distance smaller, postpetiole narrower and lower. Discriminant < 0 [error 0% in 61 specimens]

27

 * With sqPDg in µm and all other measurements in mm, discriminant 163.54*PoOc+0.755*sqPDg-57.89*CL-58.26*CW+197. 78*EYE+47.39*FRS-54.85*SP+55.08*PeW-109.15*PeH+53.45*PpH-178.59*PLg-4.19 > 0.5 [error 0% in 84 specimens]. S Balkans and Asia Minor. Figs. 42–45 Cardiocondyla bulgarica
 * Discriminant < 0.5 [error 0% in 95 specimens]

28

 * Microsetae on clypeus shorter (Fig. 46), pubescence on all body parts shorter, foveolae on vertex less densely packed (Fig.49), postpetiole wider, petiole node in lateral view more symmetric (Fig.47), dorsum of mesosoma and waist shiny and mesosoma frequently darker. With dFOv in µm and all other measurements in mm, discriminant 0.965*dFOv+164.79*EYE-38.64*PpW+123.49*PLg +77.67*Mgr-32.49 < 0 [error 2.9% in 69 specimens]. SE Balkans, Asia Minor, Israel, Caucasus, Caspian region, Iran, Afghanistan, Kyrgistan. Figs, 46–49 Cardiocondyla sahlbergi
 * Microsetae on clypeus longer (Fig. 50), pubescence on all body parts longer, foveolae on vertex more densely packed (Fig. 53), postpetiole narrower, petiole node in lateral view more asymmetric (Fig. 51), dorsum of mesosoma and waist less shiny and mesosoma frequently lighter. Discriminant > 0 [error 7.7% in 26 specimens]. georgia, Iran. Figs 50–53 Cardiocondyla persiana

29

 * Vertex with rather large, well-demarcated, bicoronate and densely-packed foveolae and in anteromedian part with well-developed longitudinal sculpture(Figs. 38, 41). Pubescence on gaster tergites more dense. With dFOv, sqPDg in µm and SPBA in mm, discriminant 2.559*sqPDg-0.472*dFov+15.117*SPBA-4.857 < 0 [error 0% in 10 specimens]. Eqypt, Israel. Figs. 38–41 Cardiocondyla israelica
 * Vertex with smaller, less demarcated and more spaced foveolae and with very weak or absent longitudinal microsculpture. Pubescence on gaster tergites less dense. Discriminant > 0 [error 0% in 51 specimens]

30

 * Postpetiole and frons wider, pubescence hairs on gaster tergites shorter. With all measurements in mm, discriminant 93.21*FRS+27.62*PpW-406.34*PLg-6.246 > 0 [error 0% in 44 specimens]. Continuously distributed from the S Ukraine (32°E) eastwards to N Xinjang (88°E). Figs. 22–25 Cardiocondyla ulianini
 * Postpetiole and frons narrower, pubescence hairs on gaster tergites longer. Discriminant 93.21*FRS+27.62*PpW-406.34*PLg-6.246 < 0 [error 0% in 7 specimens]

31

 * Postocular distance and postpetiole height much larger (PoOc/CL > 0.423, PpH/CS > 0.260). Foveolae on vertex mediad of eye with diffuse margins (Fig. 29). Anterior face of petiole node moderately sloping down (Fig. 27). SE Kazakhstan. Figs. 26–29 Cardiocondyla littoralis
 * Postocular distance and postpetiole height smaller (PoOc/CL < 0.423, PpH/CS < 0.260). Foveolae on vertex mediad of eye more strongly demarcated and bicoronate (Fig. 33). Anterior face of petiole node steeper (Fig. 31). Iranian Caspi region. Figs. 30–33 Cardiocondyla caspiense