Bull. Natl. Mus. Nat. Sci., Ser. B, 41(4), pp. 179–182, November 20, 2015

Floral Visitors of Eriocaulon heleocharioides (Eriocaulaceae),an Extinct Aquatic Species in the Wild
Norio Tanaka1,*, Hiroki Ono2 and Shoh Nagata3
1

Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
2
Marine Biology Research Division, Scripps Institution of Oceanography, University of California,
San Diego, 4325 Hubbs Hall, La Jolla, CA 92093, USA
3Speciﬁed Nonproﬁt Corporation AQUA CAMP,
Shimohiro-oka 670–126, Tsukuba, Ibaraki 305–0042, Japan* E-mail: ntanaka@kahaku.go.jp(Received 30 July 2015; accepted 24 September 2015)

Abstract Insects were observed visiting the inﬂorescences of Eriocaulon heleocharioides(Eriocaulaceae), an extinct aquatic species in the wild, at Sanuma Lake, Japan. Twenty-three ﬂoral
visitors to E. heleocharioides belonging to three orders, four suborders, and ten families were collected. Of them, members of the order Diptera-suborder Brachycera accounted for 74% and thoseof the suborder Nemato accounted for 17%. The E. heleocharioides visitors were hygrophytes andterrestrial species.
Key words : aquatic plant, Eriocaulon heleocharioides, extinct species in the wild, pollination.

Introduction
Eriocaulon heleocharioides Satake (Eriocaulaceae) is an annual aquatic herb endemic to Japanand is an extinct species in the wild (Ministry ofthe Environment, 2012). This species disappeared from its last habitat in the Sanuma Lake,
Shimotsuma City, Ibaraki Prefecture, Japan,
immediately after a change in water managementin 1994 and has only been preserved ex situ
(Tanaka et al., 2014). Since 2008, a project toreturn this species at the Sanuma Lake has been
conducted by the Tsukuba Botanical Garden,
National Museum of Nature and Science, Japan.
From 2009 onward, many E. hereocharioides
individuals survived and bore seeds in autumn(ca. 70 individuals in 2009, ca. 800 in 2010, ca.
13,600 in 2011).
Although the knowledge of the pollination
system is essential for the conservation of theannual species, few reports have been available

for the family Eriocaulaceae. Indirect studies
based on ﬂoral morphology have reported inconsistencies. Some authors presumed that the pollination system of the Eriocaulaceae members is
anemophily based on their ﬂoral morphologicalcharacteristics (Kral, 1966; Cronquist, 1981;
Judd et al., 2002), whereas others have speculated that it is entomophily (Dahlgren et al.,
1985; Hensold, 1988; Rosa and Scatena, 2003).
Only two studies have revealed that entomophilyis the pollination system of some Syngonanthus
species (Eriocaulaceae) using direct observations
and experiments, including Syngonanthus mucugensis and S. curralensis (Ramos et al., 2005)
and S. elegans (Oriani et al., 2009). Sawyer et al.
(2005) showed that E. parkerii relies heavily on
geitonogamy for seed production, but the pollinators of this genus remain unclear.
The male E. heleocharioides ﬂower has a nectary and its pollen grains are sticky. These ﬂoral
morphological characteristics argue regarding

Norio Tanaka et al.

180

entomophily. In this study, we identiﬁed insects
that visited the inﬂorescences of this species in awild habitat.
Materials and Methods
The study site was Yanagi Wando, Sanuma
Lake, Shimotsuma City, Ibaraki Prefecture,
Japan. Seeds of E. heleocharioides have been
reintroduced to this site since 2009, and sevensmall communities (ca. 22 m2; ca. 13,600 individuals) have been regenerated as of 2011. Theobservations were conducted within two of thesecommunities. One was a 3 m2 area with 1,920
individuals and the other was 9 m2 area with
6,354 individuals. The two sites were located at 3m from each other.
We observed the insects that visited the inﬂorescences of E. heleocharioides from 9 a.m. to 5
p.m. between 26 September and 30 September,2011. We observed through the night only on 30
September. Almost all E. heleocharioides in theSanuma Lake were ﬂowering during this period.
Insects that visited the inﬂorescences were colTable 1.

lected after they moved among the ﬂowers andwere preserved with naphthalene in silica gel.
The number of pollen grains attached to theinsects that were collected was measured using astereoscopic microscope.
Results and Discussion
Twenty-three ﬂoral visitors to E. heleocharioides belonging to three orders, four suborders,
and ten families were collected (Table 1, Fig.
1A). Of them, members of the order Diptera-suborder Brachycera accounted for 74% and thoseof the suborder Nemato accounted for 17%. Thenumber of pollen grains attached to the insects
varied from 0 to 50 for each individual. Most ofthe pollen grains were found around the body orlegs, but for Hymenoptera they were foundaround the mouth (No. 22 in Table 1).
Dipterans were the main visitors to E. heleocharioides in the Sanuma Lake. No reports areavailable on the genus or species of the pollinators. Previous studies have reported that theorders Coleoptera and Hymenoptera are pollina-

Floral visitors of Eriocaulon hereocharioides and the number of pollen grains attached to the visitors

IndividualNo.

OrderSuborder

Family1234567891011121314151617181920212223

Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
Diptera
DipteraHymenoptera
Hemiptera

Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
Brachycera
NematoNematoNematoNematoSymphyta
Homoptera

Ephydridae
Ephydridae
Ephydridae
Ephydridae
Ephydridae
Ephydridae
Ephydridae
EphydridaeEphydridae
Ephydridae
Tachinidae
Sciomyzidae
Sarcophagidae
Sarcophagidae
Calliphoridae
Calliphoridae
Syrphidae
Ceratopogonidae
Ceratopogonidae
Ceratopogonidae
Culicidae
Tenthredinidae
Cicadellidae

Genus

Ochthera
Ochthera
Ochthera
Ochthera
SepedonLucilia
Lucilia

Species

The numberof attachedpollen grains

sp.-A
sp.-A
sp.-A
sp.-B
sp.-B
sp.-B
sp.-C
sp.-C
sp.-C
sp.-C
sp.-D
sauteri
sp.-F
sp.-G
caesarcaesar
sp.-H
sp.-I
sp.-I
sp.-I
sp.-J
sp.-K
sp.-L

3
10050–
24401
0
10–20
2551211102030

Floral Visitors of Eriocaulon heleocharioides

181Fig. 1. A. Ephydridae sp. visiting Eriocaulon heleocharioides at Sanuma Lake. B. Inﬂorescences of Eriocaulon
heleocharioides. a: anther of male ﬂower, n: nectary of male ﬂower, s: stigma of female ﬂower.

tors of some Syngonanthus species (Oriani et al.,2009; Ramos et al., 2005).
Inﬂorescences of the Eriocaulaceae usuallyconsists of many male and female ﬂowers bornein dense heads. Only the number of stamens (4–6in Eriocaulon and 2–3 in Syngonanthus) andappendices of female ﬂowers (absent in Eriocaulon and present in Syngonanthus) (Stutzel, 1998)
differ between Eriocaulon and Syngonanthus. Itis uncertain whether the difference in visitors is
because of the basic ﬂoral morphology of thesegenera. Future studies on Eriocaulaceae pollinators may reveal whether the pollinators are associated with ﬂoral morphology, the faunal habitat,or other factors.
Eriocaulon and Syngonanthus species arehygrophytes or submerged. E. heleocharioides
inhabits underwater areas in spring and summer
and marshes during autumn. Of the visitors identiﬁed in this study, Sepedon sauteri (Sciomyzidae) lives under water around paddy ﬁelds(Nagatomi and Kushigemachi, 1965). Most Ochthera (Ephydridae) adults are found near water(streams, rivers, and lake shores) and most larvae
are aquatic or semi-aquatic (McAlpine et al.,1987). In contrast, Lucilia caesar (Calliphoridae)
widely inhabits urban areas and forests. Althoughprevious studies about Syngonanthus did notrefer to the habitats of the pollinators, the visitors
to E. heleocharioides were not limited to hygrophytous insects. If terrestrial visitors, such as L.
caesar, are effective pollinators, they will pollinate E. heleocharioides even if the environment
surrounding the Sanuma Lake is urbanized in thefuture. E. heleocharioides has nectary at thebasal part of sterile pistil in a male ﬂower. Mostof visitors except for the Ochthera of Diptera,Hymenoptera and Hemiptera, suck nectar(McAlpine et al., 1987). Because these visitors
did not accidentally perch on the inﬂorescences,
they would be expected to visit there constantly.
We showed that most of the insects that visitedE. heleocharioides probably transported some ofthe pollen grains among its ﬂowers and/or inﬂorescences. However, because the number of pollen grains attached to the insects varied withineach species and the number of samples was
small, the effectiveness and contribution of eachspecies could not be assessed. A more detailed
study in the future is necessary to resolve thesepoints.
Seed propagation of E. heleocharioides after
its reintroduction into the wild is essential forin situ conservation. Our results provide basic
information to determine the pollination system
and reproductive ecological traits of E.

Norio Tanaka et al.

182

heleocharioides.
Acknowledgment
The authors thank Tomoko Obata, SaoriIchikawa, Kohei Suzuki, Takashi Kamijo, andToru Nakamura for help with conducting theresearch project; Kazuo Mochizuki and Futoshi
Miyamoto for providing seeds from Sanuma
Lake; Yoshiyuki Sugaya, Fumio Uchiyama, andShimotsuma city for improving the water management. The authors are thankful for grants toTsukuba Botanical Garden from the Ministry ofEnvironment (The ex situ conservation modelproject).
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