Formerly, Sauropus (van Welzen, 2003) was a separate genus of which the species are not pollinated by moths. Based on phylogenetic analyses (Pruesapan et al. 2008, 2012) both genera had to be united under the oldest name Breynia (van Welzen et al. 2014). Former Sauropus is now divided over Breynia subgen. Breynia sect. Cryptogynium Welzen & Pruesapan and Breynia subgen. Sauropus Welzen & Pruespan (Fig. 1A).

Both genera were formerly separated because of the strong differences in floral morphology in both sexes. The flowers of both sexes in former Sauropus are usually flat, open and disc-like. The staminate flowers (Fig. 3a) have six sepals, basally to almost completely united; they lack nectar glands, but (usually) have scales inside, which are probably transformed disc glands. The scales keep the flower closed when the stamens are still immature. The filaments of the three stamens are basally united into a column, but at the top they form three, ± horizontal, free arms with the anthers underneath. The ovary of the pistillate flowers (Fig. 3b) has a flat top, on which there are three, well-developed stigmas that are usually flat and split at the apex and resemble a crescent-moon with papillae to catch pollen (Fig. 3c). Exceptions are that, in some species, the stigmas are erect and, in some, the staminate flowers lack the scales, but instead they have three sepals that are folded inwards and the stamens are enlarged and point diagonally upwards. The potential pollinators of these ‘Sauropus-flower’ species have not yet been elucidated by any study.

Figure 3. 

Breynia J.R.Forst. & G.Forst. non-moth-pollinated flowers a staminate flower of B. bicolor (Craib) Chakrab. & N.P.Balakr. (subgen. Breynia sect. Cryptogynium) with clear scales and androecium (re-used with permission, Flora of Thailand 8, 2: fig. 72F. 2007). – B. lithophila Welzen & Pruesapan (subgen. Sauropus) b pistillate flower c gynoecium with papillae (re-used with permission: Thai Forest Bulletin (Botany) 38: 116, fig. 3. 2010) (a Maxwell 96-712 b Phonsena, Chusithong, de Wilde & Duyfjes 5594; both in L). Illustrations by: a Jan van Os, 2002 b, c Anita Walsmit Sachs, 2009.

Breynia subgen. Breynia sect. Breynia (Fig. 1A) is pollinated by moths (Kawakita and Kato 2004b, 2009). The staminate flowers are narrow and campanulate, with united sepals forming a tube, with the disc scales on the top inside (sometimes the sepal lobes are reduced to a thickened ring and the scales resemble the calyx lobes; Fig. 4a). Within the tube, three stamens are united into a massive stalk (androphore) with the anthers orientated vertically along it (Fig. 4b). The pistillate flowers are less open than in former Sauropus, but the main difference is in the stigmas. The style is lacking and the stigmas are greatly reduced in size, sometimes completely split (Fig. 4c). In some species, there are six short vertical stalks on top of the ovary without any stigmatic papillae. Only two species in this section, B. fruticosa (L.) Müll.Arg. and B. glauca Craib (Fig. 4), still have larger stigmas, but these are not united in a style.

Figure 4. 

Breynia glauca Craib a staminate flower with scales slightly upright, calyx lobes reduced to thickened ring b idem with part of calyx removed, showing androecium c pistillate flower with three entire stigmas, style absent. Illustrations by Jan van Os, 2002. Re-used with permission of the Flora of Thailand (Flora of Thailand 8, 1: fig. 30B–D. 2005).

Furukawa and Kawakita (2017) showed that a gynophore (of variable length) often develops after fruit set in B. officinalis Hemsl. on Amami-Oshima Island (Ryukyu Islands, Japan), also mentioned by Zhang et al. (2012), which likely precludes overconsumption by Epicephala vitisidaea Li, Wang & Zhang, 2012, as the larvae have to eat their way up through the gynophore (unfortunately, they used the name B. vitis-idaea (Burm.f.) C.E.C.Fisch., a species not present in the Ryukyu Islands and southern China and which definitely lacks a gynophore; see van Welzen and Esser (2005)).

Seemingly, in comparison to the outgroup, the flowers in the ancestral species of sect. Breynia evolved in response to moth pollination: the staminate flowers became closed, campanulate and, inside, the anthers became vertical with united stamens (Fig. 4a, b); in the pistillate flowers, the stigmas are strongly reduced (Fig. 4c). Breynia retusa shows a reversal towards a normal style and stigma (Fig. 5c), thus likely this species underwent a host switch. Kato and Kawakita (2017: table 6.1) recorded that B. retusa is not pollinated by Epicephala moths, but the (new) pollinators are unknown. The staminate flowers of B. retusa are rather narrow (Figs 5a, b), but more open than other flowers of the moth-pollinated species.

Figure 5. 

Breynia retusa (Dennst.) Alston a staminate flower b idem, part of calyx removed, androecium and scales visible c pistillate flower with part of calyx removed, distinct style and branching stigmas visible. Illustrations by Jan van Os, 2002. Re-used with permission of the Flora of Thailand (Flora of Thailand 8, 1: fig. 29A, B, D. 2005).

Stigmatic papillae are often present in Breynia subgen. Breynia sect. Cryptogynium and Breynia subgen. Sauropus (Fig. 2c), but absent or strongly reduced in Breynia subgen. Breynia sect. Breynia (Fig. 4). The disappearance of the papillae may be another adaptation to moth pollination.

A similar situation as with Breynia occurred in these two groups. Former Phyllanthodendron Hemsl. (or Phyllanthus subgenus Phyllanthodendron (Hemsl.) G.L.Webster) is presently split into Glochidion subgen. Phyllanthodendron (Hemsl.) R.W.Bouman and G. subgen. Pseudoactephila (Croizat) R.W.Bouman. These two taxa are not moth-pollinated (Fig. 1A; Kato and Kawakita (2017)). The staminate flowers of former Phyllanthodendron are rather open, with five or six basally connate sepals with an attenuate apex (Fig. 6a, b), the disc glands are often large and somewhat petal-like, the generally three stamens have connate filaments and diverging upper parts and the connectives have an apical appendage. The pistillate flowers (Fig. 6c, d) have similar sepals and disc glands as the staminate flowers and on top of the ovary are well-developed stigmas (often with a short style) that are apically entire or shortly bifid.

Figure 6. 

Glochidion minutiflorum (Ridl.) R.W.Bouman (formerly Phyllanthus (subg. Phyllanthodendron) ridleyanus Airy Shaw a staminate flower which has three outer sepals with elongated apices b idem, part of sepals removed, petaloid disc glands visible and stamens with appendices on the connectives c pistillate flower d pistillate flower with part of sepals removed, petaloid disc glands visible and hairy ovary with the stigmas on top (a, b Kiew & Anthonysamy 2977 c, d Stone 9494; both L). Illustrations by Esmée Winkel, 2021.

In subgenus Glochidion, which is moth-pollinated, flowers of both sexes lack a disc. The staminate flowers (Fig. 7a) are campanulate and the androecium resembles that of Breynia (Fig. 5b) as the filaments are vertical and tightly together with the anthers along them and the connectives have apical appendages that form a pyramidal cone. When wilting, the stamens start to detach from each other and bend outwards and then resemble the stamens of the staminate flowers in Glochidion subgenera Phyllanthodendron and Pseudoactephila. In the pistillate flowers (Fig. 7b, c), the stigmas are upright and united into a cone terminating in the often slightly split apices of the stigmas that form a cavity in the middle where the female moth deposits the pollen (Fig. 7b, c).

Figure 7. 

Glochidion rubrum Blume a staminate flower with sepal removed, androecium of adnate stamens with apically appendaged connectives b pistillate flower c gynoecium with upright, united stigmas with central cavity. Drawing: Jan van Os, 2003. Re-used with permission of the Flora of Thailand (Flora of Thailand 8, 2: fig. 5C–E. 2007).

As with the first group (Breynia, including former Sauropus), the differences in flower morphology led to this group being separated into two genera. Based on the phylogeny (Bouman et al. 2021) and the resulting new classification (Bouman et al. 202), both former genera are now united under Glochidion (Phyllanthodendron was paraphyletic and Glochidion is the older name). The staminate flowers in subgenus Glochidion (Fig. 1A) are narrower than in the other two subgenera with more strongly united stamens and the connective appendages touching, while in the pistillate flowers, the stigmatic surface is reduced by uniting the stigmas into an erect pyramidal structure. In both sexes, the disc/disc glands are gone, as seemingly the moths do not need a nectar stimulus. As in Breynia, there is one Glochidion species, G. sericeum (Blume) Zoll. & Moritzi, showing a reversal, not in the staminate flowers (Fig. 8a, b) but in the pistillate flowers, where a well-developed style (covered by the sepals) with free, spreading stigmas is present (Fig. 8c, d); Kato and Kawakita (2017: fig. 10.2) did not record any Epicephala moth on this species.

Figure 8. 

Glochidion sericeum (Blume) Zoll. & Moritzi a staminate flower b staminate flower with part of sepals removed, showing adnate stamens c pistillate flower with a reduced number (2) of sepals d pistillate flower with sepal removed showing well-developed style and stigmas (Sinclair 10680, L). Illustration by Esmée Winkel, 2021.

Cicca L. is separated from Phyllanthus (Bouman et al. 2022) and restricted to a few subgenera, most of which are only found in Madagascar. Of the local outgroup, Cicca subgenus Betsileani (Jean F.Brunel) R.W.Bouman, only C. betsileani (Leandri) R.W.Bouman could be studied, a non-moth-pollinated species. Its flowers are open with six thin sepals; the staminate flowers have six disc glands and three free stamens; the pistillate flowers have a 3-locular ovary bearing terminal, well-developed, spreading stigmas that are split in the upper 2/3.

Cicca subgenus Menarda (Comm. ex A.Juss.) R.W.Bouman has staminate and pistillate flowers with 5(6) sepals; the staminate flowers have separate disc glands and three or five stamens; the pistillate flowers show a circular disc or separate disc glands and a 3-locular ovary (a revision and drawings can be found in Ralimanana and Cable (2020)). In Kato and Kawakita (2017), subgenus Menarda is represented by Cicca humbertii (Leandri) R.W.Bouman and C. marojejiensis (Leandri) R.W.Bouman (latter not included in this study) as being moth-pollinated. Various species of subgenus Menarda were investigated. Morphologically, Cicca humbertii (Leandri) R.W.Bouman, C. perrieri (Leandri) R.W.Bouman (Fig. 9) and C. sambiranensis (Leandri) R.W.Bouman have staminate flowers with (rather) stiff, upright sepals, making the flowers narrow and three united filaments with anthers vertically along the androphore in C. humbertii, but five free stamens (Fig. 9a) in the other two species (at least close together in young flowers of C. sambiranenensis); the pistillate flowers have the stigmas united into an upright cone with a narrow opening between them (Fig. 9b).

Figure 9. 

Cicca perrieri (Leandri) R.W.Bouman a staminate flower with part of sepals removed showing free, upright stamens b pistillate flower with part of sepals removed showing upright, united stigmas (Gautier LG 3009, WAG). Illustration by Esmée Winkel, 2021.

Cicca coodei (Ralim. & Petra Hoffm.) R.W.Bouman and C. cryptophila (Comm. ex A.Juss.) R.W.Bouman, also in subgenus Menarda, have rather open staminate flowers with free stamens and the stigmas in the pistillate flowers are on a short style, but well-developed and spreading and clearly split halfway.

Unlike in the previous two groups, the switch to moth pollination resulted in less distinct differences in the flowers; therefore, the moth- and non-moth-pollinated species had not been divided into separate genera. In comparison to the former two groups, C. betsileani, C. coodei and C. cryptophila conform in their morphology to non-moth-pollinated with open flowers with either well-developed stigmas or free, spreading stamens. Cicca cryptophila is in the basal clade of subgenus Menarda (Bouman et al. 2022: suppl. fig. 1). The other three species, C. humbertii, C. perrieri and C. sambiranensis, are in higher clades. Their pistillate flowers are similar to those of the moth-pollinated subgenus Glochidion in the cone-like united stigmas. Their staminate flowers have narrow, stiff sepals, but differ in the degree of connation of the stamens.

As few species could be observed, it is not possible to show where in the Cicca group moth pollination started, but likely between the basal group (with C. cryptophila) and the upper clades (which partly form a trichotomy).

Due to the high similarity with the pistillate flowers of Glochidion, several of the species in Cicca were formerly described or transferred to Glochidion (see Leandri (1937); Hoffmann and McPherson (2003)), but generally differ in the presence of disc glands, which are absent in Glochidion (Table 2).

With this group, Cicca betsileani can serve as a non-moth-pollinated outgroup; see the previous group for a short description.

Dendrophyllanthus S.Moore sect. Dendrophyllanthus is a New Caledonian group that comprises moth- and non-moth-pollinated species (Table 2) based on the comparison with the outgroup. However, the staminate flowers were often not seen or were young and in bud. They do not present a clear picture of morphological adaptations. The stamens are generally erect and free to completely united (Table 2). The pistillate flowers show either large, well-developed stigmas, generally free and sometimes recurved, or the stigmas are erect, free or united, sometimes small, in a tight upright circle with the stigmatic tissue on the inside (Table 2). Dendrophyllanthus clamboides (F.Muell.) R.W.Bouman (Fig. 10) shows united stamens and stigmas and is likely moth-pollinated like D. glochidioides (Elmer) R.W.Bouman with partly free stamens (Fig. 11). The interpretation that united stamens and stigmas are indicative of moth pollination is not necessarily always correct. Dendrophyllanthus buxoides (Guillaumin) R.W.Bouman and D. caudatus (Müll.Arg.) R.W.Bouman are recorded by Kawakita and Kato (2004a) to be moth-pollinated, but their sturdy stigmas point at the opposite conclusion, though the stigmas are more or less upright (slightly spreading) and, in case of D. caudatus, bent inwards towards each other (only seen in young fruit). Dendrophyllanthus wilkesianus (Müll.Arg.) R.W.Bouman (Fig. 12) shows more or less united stamens (but small anthers with horizontal slits), but free, recurved, papillate stigmas and likely is not moth-pollinated.

Figure 10. 

Dendrophyllanthus clamboides (F.Muell.) R.W.Bouman a staminate flower with part of sepals removed showing disc glands and united stamens b pistillate flower with part of sepals removed showing disc glands and united stigmas (a Carr 15875 b NGF (Vandenberg, Womersley & Galore) 42044; both L). Illustration by Esmée Winkel, 2021.

Figure 11. 

Dendrophyllanthus glochidioides (Elmer) R.W.Bouman a staminate flower with part of sepals removed showing disc glands and partly united stamens b pistillate flower with part of sepals removed showing disc glands and united stigmas (a PNH (Edaño) 40177 b PPI (Stone et al.) 24; both L). Illustration by Esmée Winkel, 2021.

Figure 12. 

Dendrophyllanthus wilkesianus (Müll.Arg.) R.W.Bouman a staminate flower with partly removed sepals showing disc glands and the united stamens with small anthers with horizontal slits b pistillate flower with part of sepals removed, showing disc glands and well-developed, free, recurved, papillate stigmas (a A.C. Smith 6294 b A.C. Smith 9630; both L). Illustration by Esmée Winkel, 2021.

Unfortunately, the published phylogenies for this group either only contain moth-pollinated species (Kawakita and Kato (2009), as Phyllanthus subgen. Gomphidium sect. Adenoglochidion) or show a basal polytomy (Bouman et al. 2021). This means that it is uncertain where moth pollination started in the phylogeny and if there are species reversing to non-moth pollination. Additionally, due to lack of material, not all species mentioned by Kawakita and Kato (2004a, 2009) could be analysed.

Dendrophyllanthus S.Moore sect. Leptonema (Baill.) R.W.Bouman is an Australian–New Caledonian group that shows the same developments as the previous group. Again, C. betsileani, which has free stigmas, can serve as the outgroup. The staminate flowers do not show any obvious morphological adaptations to moth-pollination and the pistillate flowers show either well-developed spreading stigmas or cone-like, united or free, upright stigmas (Table 2). Thus, some of the species in this group may already have adapted to moth pollination, some not. Kawakita and Kato (2004a, as Phyllanthus subgen. Gomphidium sect. Gomphidium) listed a number of moth-pollinated species and three non-moth-pollinated species. The overlap with the species investigated here is very small with only two moth-pollinated species, of which D. aeneus (Baill.) R.W.Bouman has pistillate flowers that are adapted to moth pollination, but D. vulcani (Guillaumin.) R.W.Bouman seemingly has not (yet) adapted morphologically as it has well-developed, spreading stigmas.

The phylogeny of Kawakita and Kato (2009) included only moth-pollinated species, whereas the phylogeny of Bouman et al. (2021) showed that, perhaps in part of the clade, with D. ligustrifolius (S.Moore) R.W.Bouman at the base, a switch to moth pollination occurred, because D. ligustrifolius likely is moth-pollinated (Fig. 13) and D. hypospodius (F.Muell.) R.W.Bouman (Fig. 14) and D. serpentinus (S.Moore) R.W.Bouman likely are not moth-pollinated. Unfortunately, the upper part of the clade comprises a few polytomies and weakly-supported branches, thus this may change in the future when more species and/or markers are added. In this group, D. bupleuroides (Baill.) R.W.Bouman, D. kanalensis (Baill.) R.W.Bouman and D. loranthoides (Baill.) R.W.Bouman are probably not moth-pollinated; D. vulcani is disputable (it seems to have moth pollination (Kawakita and Kato 2004a, 2009), but is morphologically not adapted); D. aeneus, D. guillauminii (Däniker) R.W.Bouman and D. ligustrifolius have moth-pollination; and the pollination of D. favieri (M.Schmid) R.W.Bouman and D. unifoliatus (M.Schmid) R.W.Bouman is unknown.

Figure 13. 

Dendrophyllanthus ligustrifolius (S.Moore) R.W.Bouman a developing fruit with stigmas erect and closed b dehiscing fruit with non-papillate stigmas recurved (a MacKee 19634 b McPherson 5025; both L). Illustration by Esmée Winkel, 2021.

Figure 14. 

Dendrophyllanthus hypospodius (F.Muell.) R.W.Bouman a staminate flower with free stamens b pistillate flower with free, recurved stigmas (Bruhl et al. 1123, L). Illustration by Esmée Winkel, 2021.

In Kirganelia, section Pseudomenarda (Müll.Arg.) R.W.Bouman is the non-moth-pollinated outgroup to section Kirganelia, where moth pollination is recorded. Section Pseudomenarda is a small taxon with two species, of which K. somalensis (Hutch.) R.W.Bouman (Fig. 16) was seen. It shows staminate flowers of 2.5–3 mm in diameter with five sepals, five disc lobes, two outer free and three inner united stamens. The pistillate flowers are very open, ca. 3.5 mm in diameter, with five relatively large sepals, a broad, ring-like disc and a 5-locular (can be 3-locular; see Hutchinson (1912)) ovary with a terminal, ca. 0.3 mm long style and then five horizontally spreading stigmas ca. 1 mm long, split in the upper third.

Section Kirganelia, Kirganelia reticulata (Poir.) Baill. was reported to be moth-pollinated (Kawakita et al. 2015; Fig. 15). The staminate flowers are very small and inconspicuous (ca. 2 mm in diameter) with five or six sepals in two whorls, five or six small disc glands and five or six stamens in two very tight whorls, outer two or three free, inner three with filaments basally connate; these staminate flowers are usually found unopened in dried specimens. The pistillate flowers have the same number of sepals and disc lobes as the staminate flowers, the ovary is small with four or five short stigmas, slightly split apically, bent towards each other and forming a circular cone that is open on the inside. Kawakita et al. (2015) reported that six moth species visit the flowers of K. reticulata, of which three have become parasitic again, causing the ovules/fruits to gall and one species also induces the fruit to become inflated. A possible reason for the reversal to parasitism is protection against predation by specialised braconid wasps (Kawakita et al. 2015). Predation by the wasps is likely as K. reticulata has relatively small fruits (ca. 4.5 mm in diameter), thus long ovipositors are not needed.

Figure 15. 

Kirganelia reticulata (Poir.) Baill. a staminate flower with part of sepals removed, showing disc glands and two layers of united stamens b pistillate flower with part of sepals removed showing small disc glands and small, upright, split free stigmas bent towards each other (a Maxwell 91-1025 b Put 2297; all L). Illustration by Esmée Winkel, 2021.

Figure 16. 

Kirganelia somalensis (Hutch.) R.W.Bouman a staminate flower, closed b staminate flower with part of sepals removed showing disc glands and free stamens c pistillate flower with part of sepals removed showing flat, circular and indistinct disc and well-developed, horizontal free stigmas (Kilian 1718 & Lobin 6572, WAG). Illustration by Esmée Winkel, 2021.

Adaptation in flower morphology of K. reticulata for moth pollination is seemingly only visible in the pistillate flowers; the staminate flowers with tightly, vertically grouped stamens are, at most, smaller than those in other species and then less accessible for various groups of insects. As in Breynia section Breynia, the stigmas in the pistillate flowers are shorter and, as in Glochidion, the stigmas are united, upright and short, forming an erect ring on top of the ovary and forming a depression inside. In contrast, in section Pseudomenarda, the stigmas are still well-developed and spreading. Additionally, some species within the genus, belonging to the now-subsumed group Phyllanthus section Hemicicca (Baill.) Müll.Arg., possess different flower features; especially K. flexuosa (Siebold & Zucc.) R.W.Bouman, which has staminate flowers with reddish, spreading sepals and two free stamens (see Kato and Kawakita (2017)). Their pollinators are unknown.

As a result of obligate leafflower moth pollination, adaptations in the morphology of staminate and pistillate flowers were expected because they can improve pollination efficiency and the fit with the moths, while also optimising pollen uptake, pollen deposition and oviposition for the pollinators. However, because the mutualistic relationship has evolved several times in tribe Phyllantheae, there could be differences in morphological adaptations or similar morphological patterns in the different groups could have arisen through convergent evolution. Recent studies have shown that the mutualism between leafflowers and leafflower moths is more complex than first described (Kato et al. 2003) as there are differences in the level of species specificity (Kawakita and Kato 2004a, 2006; Zhang et al. 2012; Li et al. 2015; Yang and Li 2018), cheaters of the mutualism (Kawakita et al. 2015; Wang et al. 2020) and defences against this antagonistic relationship (Goto et al. 2010; Furukawa and Kawakita 2017). Furthermore, possible reversals in flowers are indicated here.

Flowers associated with the obligate moth pollination mutualism show, as a visual stimulus to attract the nocturnally active Epicephala moths, a contrast between the light (green to yellowish) sepals and the dark night sky, but this is also observed in non-moth-pollinated flowers. Olfactory cues were detected in a number of studies, differences that likely promoted speciation as they differed either in strength or composition between the sexes (Svensson et al. 2010; Okamoto et al. 2013; Okamoto 2017; Huang et al. 2015; Zhang et al. 2016). Okamoto et al. (2007; see also Okamoto (2017)) showed that Glochidion subgenus Glochidion produces floral odours, often typical of each species, but different between flower sexes, that attract the female moths. Additionally, Breynia vitis-idaea (Burm.f.) C.E.C.Fisch. produces two floral odours. Attractants are likely crucial, especially during the nocturnal pollination and differences in smell between the sexes can help guide the moth first to the staminate and later the pistillate flowers. Therefore, nectar glands like the disc or disc glands may still be as important as the tissue to emit the odours; the moths themselves do not seek nectar and the plants likely do not attract other insects. The glands/discs are present in most Phyllantheae, except in Glochidion subgenus Glochidion and Breynia; in these taxa, perhaps the receptacle produces the odour. The two other subgenera of Glochidion (Pseudoactephila and Phyllanthodendron) have disc glands in the flowers, but these have become almost petal-like and likely are not producing nectar any longer.

The majority of the moth-pollinated flowers are small with no bright colours, while the narrow shape of many is geared more towards a mechanical fit to the pollinator. The adaptations in staminate flowers that seem most common are a tight, cylindrical ring of sepals, with united, or at least upright, stamens with the anthers vertically along the androphore (opening towards the sepals) or with the anthers at the top of the androphore. This is especially demonstrated in Breynia section Breynia and Glochidion subgenus Glochidion (groups 1 and 2, respectively). With herbarium material, it is difficult to access the tightness of the sepals; therefore, this is often not noted, except when the sepals are thick and upright like several species in Cicca subgenus Menarda (group 3), Pyllanthus graveolens (Phyllanthus subgenus Conami; group 7) and several species in Phyllanthus subgenus Microglochidion (Group 8). If the staminate flowers produce a tight calyx cylinder, then as soon as the moth probes with its proboscis, covered with sensilla, the sensilla become dusted with pollen. This seemingly is a very effective mechanism.

Female moths have to transfer the pollen to the pistillate flowers, which is generally facilitated by the plant as most Phyllantheae species are monoecious and may have fascicles with both sexes (often many-flowered in Glochidion), whereby the sexes can be receptive at different moments, or the sexes are separated in space on one branch with the staminate flowers proximally and the pistillate flowers distally (often in Breynia and Phyllanthus s.l.). A few species are reported as dioecious, but this is not easy to judge from herbarium specimens; it can also be the result of dichogamy (an extended separation in time as the staminate flowers usually develop later than the pistillate flowers). For the placements of the different sexes along branches in the various species in Thailand, see for Breynia: van Welzen and Esser in van Welzen (2007), for Glochidion: van Welzen (2007) and for Phyllanthus s.l.: Chantaranothai (2007).

In the pistillate flowers, the upright, closely set sepals and the reduced stigmatic surface may serve two functions, to facilitate the pollen transfer and to preclude visits by insects other than leafflower moths. Two reversals (Breynia retusa and Glochidion sericeum) show that well accessible, completely developed and spreading stigmas no longer attract moths. A reduction in the style length and stigmas spreading was shown as an indicator of Epicephala pollination by Kawakita and Kato (2009: fig. 2). The reduction of the stigmatic tissue is achieved in two ways, either by shortening the stigmas or by folding the stigmas into a vertical (pyramidal) cone with a small, apical opening where the female moth can deposit the pollen. A reduction of the stigmas is seen in Breynia section Breynia. Kirganelia reticulata seems to follow both strategies: the stigmas are short and folded together. All other groups show cone-like united stigmas as in Glochidion. Several moth-pollinated South American species of Phyllanthus may still have well-developed, spreading stigmas (Kawakita et al. 2019; see below). Additionally, the stigmatic papillae seem to disappear in the moth-pollinated species; compare Fig. 3 (Breynia lithophila Welzen & Pruesapan, not moth-pollinated) with Fig. 4 (Breynia glauca Craib, moth-pollinated).

The taxa included here have been shown by other authors to be pollinated and/or parasitised by Epicehala. However, several taxa display similar morphological adaptations to those treated here and future studies might uncover new instances of plants in tribe Phyllantheae in a mutualistic relationship with Epicephala moths. The main pollination system in Nymphanthus Lour. has not yet been uncovered. Kawakita and Kato (2009) reported miscellaneous observations of dipterans visiting the typical cross-shaped flowers, but this has not been confirmed. However, species of N. section Scepasma (Blume) R.W.Bouman have very different flowers with erect sepals and N. lamprophyllus (Müll.Arg.) R.W.Bouman, for example, has a long style with small stigma lobes at the top. Similarly, pistillate flowers of Emblica rufuschaneyi (Welzen, R.W.Bouman & Ent) R.W.Bouman also have a long stylar column and a reduced disc (Bouman et al. 2018). Other species of Emblica usually have well-developed spreading stigmas, but whether they are associated with Epicephala is not well known.

Adaptation to moth pollination seems to be comparatively more pronounced in the Palaeotropics (and Pacific islands) in what was formerly known as Breynia (B. subgen. Breynia section Breynia) and Glochidion (G. subgenus Glochidion) (Kawakita et al. 2019). It is often speculated that the obligate moth pollination contributed to a proliferation in species (Kato et al. 2003; Kawakita and Kato 2004a), especially in Glochidion (> 300 spp.) and New Caledonian Dendrophyllanthus (~ 160 spp.), which are speciose groups that have radiated relatively recently (see Kawakita and Kato (2009)). Breynia is somewhat less species rich, thus other factors than moth pollination likely contributed to the high speciation rate seen in these groups. The olfactory attractants may play a role (see above), but also the greater variation in flower shapes in Glochidion and Dendrophyllanthus.

In conclusion, these Palaeotropical groups show some general trends in morphological adaptation in flowers resulting from obligate moth pollination:

• Sepals are usually stiff and upright and in a tight group around either the stamens or the ovary.
• Disc and disc glands are reduced.
• Stamens are united with the anthers upright along the androphore.
• Stigmatic surface is reduced, either by reducing the length of the stigmas to short stigmas or by uniting them into a cone with an apical round opening.
• Likely stigma papillae disappear.

However, these trends are not always completely present, for example, mutualistic relationships were found in species with well-developed stigmas (see some discussions above and Table 2).

Based on the morphological trends found in the Palaeotropics, the situation in the Americas is evaluated here. Moth pollination in the Neotropics was recently reported by Kawakita et al. (2019). The moth Epicephala chancapiedra Kawakita & Kato, 2019, was found on three herbaceous species: Moeroris amara (Schumach. & Thonn.) R.W.Bouman, M. stipulata Raf. and Phyllanthus orbiculatus Rich. (Fig. 17). These three herbaceous species are pollinated by ants and as female E. chancapiedra does not have sensilla on the proboscis, the moths are (secondary) parasites, only laying eggs in the pistillate flowers without active pollination (Kawakita et al. 2019). The flowers of both sexes in these three species are small, hanging, quite open and the stigmas are generally short, but well-developed and spreading. Only the short stigmas might be an adaptation to moths, but it is more likely an adaptation to the ants or no pollination is needed as all pistillate flowers develop fruits (also in a hothouse without pollinators, but with limited seed production, pers. observ.).

Figure 17. 

Phyllanthus orbiculatus Rich a staminate flower with part of sepals removed, showing large disc gland and united stamens with small anthers with horizontal slits b pistillate flower with part of sepals removed showing large disc glands and well-developed free, horizontal to recurved stigmas (Herzog 1314, L). Illustration by Esmée Winkel, 2021.

In the genus Phyllanthus L. subgenus Ciccastrum (Müll.Arg.) R.W.Bouman (Fig. 1B) can act as a local outgroup for comparisons. This group consists of two species, P. purpusii Brandegee (Fig. 19) and P. riedelianus Müll.Arg. Both species have free stigmas that recurve over the ovary (P. purpusii) or that are bent towards each other in fruit (P. riedelianus). Only the staminate flowers of P. purpusii, each consisting of a narrow and tight cylinder of stiff upright sepals and three united stamens with the anthers apically along the androphore (like Breynia sect. Breynia), may point at moth pollination. The staminate flowers of P. riedelianus show no distinct adaptations to moth pollination (more like Breynia subg. Sauropus). However, P. riedelianus (not in the phylogeny of Bouman et al. (2021)) is doubtfully placed in this group and is strongly divergent from P. purpusii (Webster, 2002); see Torres et al. (2020).

Kawakita et al. (2019) also looked for moth pollination in four woody species in the subgenera Conami (Aubl.) G.L.Webster and Xylophylla (L.) Pers. of Phyllanthus: P. acuminatus Vahl, P. graveolens Kunth, P. huallagensis Standl. ex Croizat and P. salviifolius Kunth (Fig. 18). In all cases, the stigmas do not show reduced surfaces and the stamens are often not upright (except more or less in P. graveolens) and are, thus, usually not readily accessible to moths. The pollination relationship does not appear to be obligate as other pollinators are present (gall midges and thrips; Kawakita et al. (2019)), which may mean that the relationship with the moths is rather recent and perhaps still developing and morphological adaptations are still lacking.

Figure 18. 

Phyllanthus salviifolius Kunth a staminate flower with part of sepals removed showing disc glands and three united stamens with free small anthers with horizontal slits b pistillate flower with part of sepals removed showing disc glands and upright stigmas recurved at the apex (Breteler 3312, L). Illustration by Esmée Winkel, 2021.

Figure 19. 

Phyllanthus purpusii Brandegee a staminate flower with sepal removed showing disc glands and three united erect stamens with the anthers along the androphore b pistillate flower with sepal removed showing circular disc and spreading stigmas (Quarles van Ufford 266, U). Illustration by Esmée Winkel, 2021.

Kawakita et al. (2019) mentioned Phyllanthus L. subgenus Microglochidion (Müll.Arg.) Jean F.Brunel as a group with likely mutualistic pollination as there is some floral resemblance with Glochidion. Typical in the group is that the leaves often have a subapical extrafloral nectary abaxially, generally subapical above the mid-rib. In this group, as defined by Bouman et al. (2022), there are generally six sepals in two whorls; staminate flowers with six disc glands and three free, upright stamens; and pistillate flowers generally with a circular disc and a 3-locular ovary with the stigmas variously arranged. The situation is not completely clear as a large number of taxa could not be sampled. Not all taxa show visible morphological adaptations to moth pollination. Phyllanthus lediformis Jablonski, P. majus Steyerm., P. myrsinites Kunth (Fig. 20) and P. neblinae Jablonski have pistillate flowers with well-developed stigmas and thin sepals that generally are spreading and also have relatively large anthers and upright stamens. Phyllanthus duidae Gleason, P. pycnophyllus Müll.Arg. and P. vacciniifolius (Müll.Arg.) Müll.Arg. (Fig. 21) show an apical cone of united stigmas with three small lobes apically around a narrow opening, the typical situation as in Glochidion subgenus Glochidion; their staminate flowers have upright stamens and high stiff, upright sepals. Very likely, the species with united stigmas are moth-pollinated as the staminate and pistillate flowers show adaptations like those in other groups: limited stigma surface and narrow staminate flowers. The phylogeny of Bouman et al. (2021) only shows one representative for this group (P. vacciniifolius); thus, it is not clear if a single adaptation to moth pollination occurred in an ancestral species or multiple adaptations.

Figure 20. 

Phyllanthus myrsinites Kunth a Staminate flower with part of sepals removed showing disc glands and free stamens b pistillate flower with part of sepals removed showing ring-like disc and well-developed free and recurved stigmas (Wade Davis 14, U). Illustration by Esmée Winkel, 2021.

Figure 21. 

Phyllanthus vacciniifolius Müll.Arg. a staminate flower with part of sepals removed showing disc glands and three erect, free stamens with appendaged connectives b pistillate flower with part of sepals removed showing indistinct circular disc and upright, connate stigmas (Prance 28343, U). Illustration by Esmée Winkel, 2021.

Phyllanthus L. subgenus Xylophylla (L.) Pers. section Epistylium (Sw.) Griseb. was another taxon mentioned by Kawakita et al. (2019) as a Central American (West Indies) group that might have mutualistic relationships with Epicephala moths. Herbarium material was largely lacking; we saw only a single sheet of P. axillaris with young pistillate buds (Proctor 18349, Jamaica, U), which seem to have a closed stigma cone as in Glochidion subgen. Glochidion, which may be indicative of mutualistic pollination.

Thus, it appears that, in the Neotropics, the relationship with Epicephala moths probably is evolutionarily younger than in the Palaeotropics, because many plant species do not show strong adaptations to moth pollination and, as shown by Kawakita et al. (2019), several groups are likely not obligately moth-pollinated as other insect groups also pollinate the flowers. However, the pollination systems in the Neotropics are very understudied in comparison to those in the Palaeotropics.