Phyllium illusorium Cumming, Foley, Hennemann, Le Tirant & Büscher, 2025

Cumming, Royce T., Foley, Evelyn Marie, Hennemann, Frank H., Le Tirant, Stephane, Daawia,, Warikar, Evie Lilly, Yando, Heron, Suhartawan, Bambang, Henze, Katharina, Büscher, Thies H. & Bank, Sarah, 2025, A deeper look into the diversity of Phyllium leaf insects from Indonesia: seven new species and two unique egg morphologies (Phasmatodea, Phylliidae), ZooKeys 1256, pp. 317-370 : 317-370

Phyllium illusorium Cumming, Foley, Hennemann, Le Tirant & Büscher sp. nov.

Fig. 15

Type material.

Holotype ( ♂): Coll. I. R. SC. N. B.; Indonesia • Buton, xi. 2012, Gift from B. Kneubuhler I. G.: 32.613. Tissue sample: SB 0690 [ RBINS] . Paratype ( ♂): INDONESIEN: S-Sulawesi Provinz, Sulawesi Tenggara, Buton Island , XI. 2012. FH 0673-1 [ Coll FH] .

Differentiation.

Female, egg, and freshly hatched nymph unknown.

Male Phyllium illusorium sp. nov. are most similar to Phyllium hausleithneri and Phyllium jacobsoni due to similar femoral lobe shapes / serration, overall size and abdominal shape, and wing length / venation. Phyllium illusorium sp. nov. can be differentiated from Phyllium hausleithneri by the ventral coxae coloration, while subtle in males (and very prominent in females) Phyllium hausleithneri often have a slight purple hue to their ventral coxae surface, vs Phyllium illusorium sp. nov. which has white coxae. Male Phyllium illusorium sp. nov. are nearly indiscernible from male Phyllium jacobsoni as both species have white coxae and are very similar in most other regards (which is not surprising given their genetic close relation which was recovered in the phylogeny; Fig. 1 ). The only feature which allows consistent differentiation is the sagittal crest of the mesoprescutum which in Phyllium illusorium sp. nov. has prominent tubercles of a similar size to the anterior rim sagittal spine, vs Phyllium jacobsoni which only has small nodes along the sagittal crest. As with many phylliids, likely more prominent morphological differences are present in the egg or freshly hatched nymph stages, which are unfortunately unknown at the moment.

Descripyion. Male. Coloration. Coloration based upon the holotype and paratype specimens, which appear relatively well preserved (Fig. 15 ). Overall coloration pale green throughout with highlights of tan / reddish coloration on the margin of the protibial interior lobe, the lateral margins of abdominal segments II, III, and IV, and the tips of the antennae. Compound eyes are brown / reddish. The thorax and most of the antennae segments are straw yellow. On abdominal segment V are a pair of yellow eyespots. Ventral coxae coloration is white.

Morphology. Head capsule approximately as long as wide, with a vertex that is marked throughout with irregularly spaced and variably sized nodes. The posteromedial tubercle is singularly pointed but not particularly prominent (Fig. 15 D ). Frontal convexities are stout and bluntly pointed with sparse setae. Compound eyes large and bulbous, occupying ~ 2 / 5 of the head capsule lateral margins (Fig. 15 D ). There are three well-developed ocelli distinctly raised above the capsule and located between the compound eyes (Fig. 15 D ).

Antennae (including the scapus and pedicellus) consist of 23 segments, all segments except the scapus and pedicellus and terminal four segments are covered in dense setae where most are as long as or slightly longer than the antenna segment is wide. The terminal five segments are covered in dense short setae and the scapus and pedicellus are nearly completely bare with only a few sparse setae.

Thorax. Pronotum with anterior margin with a prominent rim which is slightly concave. Pronotum lateral margins are relatively straight and converge to a straight posterior margin that is ~ ½ the width of the anterior margin (Fig. 15 D ). Pronotum lateral margins have moderately formed rims and the posterior margin has a weakly formed rim (Fig. 15 D ). Face of the pronotum is marked by a distinct pit in the center, a sagittal furrow on the anterior ½, and slight perpendicular furrows originating from the central pit. The pronotum surface is marked throughout by low nodes (Fig. 15 D ). Prosternum and mesosternum surfaces are lumpy with distinctly formed nodes. Metasternum surface slightly wrinkled throughout, and marked with sparse granulation. Mesoprescutum approximately as long as wide, with lateral margins that are slightly converging to the posterior margin which is only slightly narrower than the anterior margin (Fig. 15 D ). Lateral margins of the mesoprescutum with eight or nine variably sized tubercles spaced unevenly, but all rather distinct (Fig. 15 A ). Mesoprescutum surface slightly raised along the sagittal plane which is marked with two distinct tubercles on the anterior 1 / 2 and two nodes on the posterior 1 / 2 (Fig. 15 D ). Mesoprescutum anterior rim distinctly raised and marked with a prominent sagittal spine; the remainder of the rim surface is relatively smooth (Fig. 15 D ). Mesopleurae begin on the anterior mesoprescutum margin and diverge at a gradually increasing angle from the anterior to the posterior but remain rather narrow throughout their length (Fig. 15 D ). Mesopleuron lateral margin with 6–8 moderately formed tubercles with one or two nodes between each set of tubercles (Fig. 15 D ). Mesopleuron face relatively smooth and marked by a distinct pit near the center and another near the anterior 1 / 3.

Wings. Tegmina moderate length, extending ½ of the way onto abdominal segment III. Tegmina wing venation: the subcosta ( Sc) is the first vein, is simple, and terminates slightly less than 1 / 2 of the way through the overall wing length. The radius (R) spans the entire length of the tegmina with the first radius ( R 1) branching ~ 2 / 5 of the way through the wing length and terminates slightly more than halfway through the tegmina length, there is also a second radius ( R 2) which branches 1 / 3 of the way through the tegmina length and runs nearly directly to the tegmina margin. The radial sector, following these branchings, runs straight to the wing apex. The media (M) also spans the entire length of the tegmina running side by side along the radius / radial sector with only a vein or two width’s gap between them. The media posterior (MP) branches off near the middle of the tegmina and runs angled towards the apex / cubitus, and the media anterior ( MA) runs straight to the tegmina apex. The cubitus ( Cu) cuts across the tegmina to the margin ~ 1 / 3 of the way through the length and runs along the edge of the tegmina where the media posterior vein fuses with it and as the cubitus reaches the apex of the tegmina it fades. The first anal ( 1 A) terminates upon reaching the cubitus ~ 1 / 3 of the way through the tegmina length. Alae well-developed in an oval fan configuration, long, reaching apical abdominal segment. Ala wing venation: the costa (C) is present along the entire foremargin giving stability to the wing. The subcosta ( Sc) is short, fusing with the costa ~ ¼ of the way through the ala length. The radius (R) spans the entire wing and branches 2 / 5 of the way through the ala length into the first radius ( R 1) and radial sector ( Rs) which run gently diverging for ~ ½ of their length, then run parallel until they near the apex where they converge slightly and terminate at the margin. The media (M) branches early, ~ 1 / 6 of the way through the ala length into the media anterior ( MA) and the media posterior (MP) which run parallel with each other throughout the central 2 / 3 of the ala length, then the media posterior fuses with the media anterior and they run fused to join with the radial sector and this fused set of veins runs to the apex where it terminates. The cubitus ( Cu) runs unbranched and terminates at the wing apex. Of the anterior anal veins, the first anterior anal (1 AA) fuses with the cubitus near the ala base and then the first anterior anal branches from the cubitus 2 / 3 of the way through the ala length where it uniformly diverges from the cubitus until it terminates at the wing margin. The anterior anal veins 2–7 (2 AA – 7 AA) have a common origin and run unbranched in a folding fan pattern to the wing margin. The posterior anal veins (1 PA – 6 PA) share a common origin separate from the anterior anal veins and run unbranched to the wing margin with slightly thinner spacing than the anterior anal veins.

Abdomen. Lateral margins of abdominal segment II parallel; III diverging with increasing degree from the anterior to the posterior; segment IV diverging strongly for the anterior 2 / 3 to the widest point of the abdomen then running parallel for the posterior 1 / 3; V through X converging gradually with nearly smooth margins (at each suture the margins angle in very slightly). Overall, the abdomen has a spade-shaped appearance.

Genitalia. Poculum broad and ends in an apex that slightly passes the anterior margin of the abdominal segment X with a margin that is straight (Fig. 15 F ). Cerci long, slender, relatively uniform in width throughout their lengths, and with slightly more than ½ of their length extending from under abdominal segment X. The cerci are nearly flat and covered in a granulose surface with numerous short setae (Fig. 15 F ). Vomer broad and stout with straight sides evenly converging to the apical hook which is thick and has a singular point (Fig. 15 F ).

Legs. The profemoral exterior lobe is narrow, with a smooth margin, and slightly thinner than the profemoral shaft width. The profemoral interior lobe is obtusely triangular and at its greatest width it is ~ 1.5 × the greatest width of the profemoral shaft. The profemoral interior lobe is ornamented four serrate teeth of similar sizes and almost evenly spaced with looping gaps between them (Fig. 15 D ). Mesofemoral exterior lobe arcs end to end but is slightly wider on the distal 2 / 3 and on the distal ¼ it is marked with two small teeth, while the proximal remainder of the lobe lacks teeth. Mesofemoral interior lobe and the mesofemoral shaft are approx. the same width, while the mesofemoral exterior lobe is ~ 1.5 × wider than the mesofemoral shaft width. The mesofemoral interior lobe, is slightly broader on the distal end and the distal end is ornamented with six small, serrate teeth while the proximal portion of the lobe is thin and lacks teeth. Metafemoral exterior lobe has a straight margin running along the metafemoral shaft and is marked with only two small teeth near the distal ¼. Metafemoral interior lobe smoothly arcs end to end with nine sharply serrate teeth on the distal 2 / 3, which is wider than the smooth proximal portion of the lobe. Protibia lacking exterior lobe, interior lobe reaching end to end in a rounded triangle with the widest portion near the middle of the length; greatest width of the lobe is ~ 1.5 × the protibial shaft width; the proximal portion of the lobe is slightly thicker than the distal portion (Fig. 15 D ). Meso- and metatibiae simple, lacking lobes completely. The probasitarsus is slightly shorter than the protibial shaft length; the mesobasitarsus is slightly longer than ½ of the mesotarsus shaft length; and the metabasitarsus is slightly <½ of the metatibial shaft length.

Measurements of holotype male [mm]. Length of body (including cerci and head, excluding antennae) 46.8, length of head 2.9, antennae 26.0, pronotum 2.6, mesonotum 2.2, length of tegmina 15.5, length of alae 37.4, profemora 9.0, mesofemora 8.5, metafemora 9.8, protibiae 6.1, mesotibiae 6.0, metatibiae 7.2.

Measurements of paratype male [mm]. Length of body (including cerci and head, excluding antennae) 49.0, antennae 27.6, pronotum 2.3, mesonotum 3.6, metanotum 3.9, length of tegmina 16.3, length of alae 37.0, greatest width of abdomen 12.3, profemora 9.2, mesofemora 8.8, metafemora 9.9, protibiae 5.8, mesotibiae 5.7, metatibiae 7.2.

Etymology.

The species epithet illusorium is the singular neuter form of the Latin illusorius, meaning mocking or ironical. While many leaf insects are colloquially described as “ walking leaves, ” Phyllium illusorium sp. nov. offers a subtle twist: it is not merely a leaf in motion, but rather a master of deception, a “ mocking leaf ” that plays with perception itself. Its intricate mimicry not only camouflages the insect among the foliage but also teases the observer, blurring the boundary between flora and fauna. The name celebrates this playful deceit, emphasizing the species’ role as a living illusionist within its arboreal habitat.

Distribution.

At present only known from the type locality; Buton Island, Southeast Sulawesi Province, Indonesia (Fig. 2 ).

Remarks.

At present this species is only known from the two type specimens from Buton island (Fig. 15 ). This species represents an interesting distribution as the other close members of its phylogenetically recovered clade ( Phyllium gardabagusi , Phyllium hausleithneri , Phyllium nisus , and Phyllium jacobsoni ) are all found west of Wallace’s line of faunal balance, while Phyllium illusorium sp. nov. is the first species from this clade found to the east (within Wallacea; Cumming et al. 2019 a).

Figures

Figure 1. Maximum Likelihood tree with focus on the phylogenetic relationships of 54 Phyllium specimens. Tree is rooted with Cryptophyllium as the outgroup. Support values are shown at each node (SH-aLRT / UFBoot). The asterisk (*) indicates maximum support (100). Newly added specimens are shown in green text and new species are highlighted in green. The blue stripes on internal branches mark dispersal to Indonesia, with blue boxes specifying the exact island or region. Abbreviations: HT, holotype; PT, paratype.

Figure 2. Distribution map for all Phyllium species used in the molecular analysis as well as the newly described species from Obi Island not represented in the phylogenetic tree. Species names of Phyllium from Malaysia, the Philippine Islands, and New Britain (Papua New Guinea) are shown in gray. The Indonesian archipelagic state is highlighted in blue and symbols of sampling sites of Indonesian Phyllium species are in dark blue. White symbols show the location of the remaining Phyllium from Malaysia, the Philippine Islands and New Britain (Papua New Guinea). The inset presents an enlarged section of Sabah (Malaysia: Borneo) and the six species found there. Abbreviations: Hal, Halmahera; Jav, Java; Kal, Kalimantan; NG, New Guinea (Papua); Ser, Seram; Sul, Sulawesi; Sum, Sumatra.

Figure 15. Phyllium illusorium sp. nov. holotype (B) [RBINS] and paratype (A, C, D, E, F) [Coll FH]. A. Detail of head and thorax, lateral; B. Holotype habitus, dorsal; C. Paratype habitus, ventral; D. Details of head, front leg, and thorax, dorsal; E. Terminalia, ventral; F. Paratype habitus, dorsal. Scale bar: 20.0 mm (B, C, E).