J. Plant Res. 114:423-427,2001
Journal of Plant Research
0 by The Botanical Society of Japan 2001
Pollination of Sarcandra glabra (Chloranthaceae) in
Natural Populations in Japan
Yayoi Tosaki', Susanne S. Rennet and Hiroshi Takahashi3*
1
2
3
Laboratory for Plant Natural History, Faculty of Science, Kanazawa University, Kanazawa, 920-1192 Japan
Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121, U.S.A.
Department of Biology, Faculty of Education, Gifu University, Gifu, 501-1193 Japan
The pollination biology of Sarcandra glabra was investiiated in its natural h a b i t in Japan. Flowers were
protogynous and stigma receptivity dropped off significantly
following anther dehiscence. Female-stage and bisexualstage flowers were visited by beetles, bees, hemiptera, flies,
and rarely ants that foraged for pollen and/or small droplets
of liquid that occasionally were secreted by the carpels and
inflorescence axes. At least the beetles, bees, and
hemiptera commonly touched the stigmas and likely effected pollination. Rowers were self-compatible, and automatic selfing sometimes occurred when pollen fell from
apical flowers onto the stigmas of lower flowers.
-
Key words: Bees - Beetles - Chloranthaceae
Flies - Pollination - Sarcandra glabra - Self-compatibility
Chloranthaceae are a family of basal angiosperms that
has received much attention from morphologists and
phylogeneticists because of their unusual flowers and fossil
record that goes back to the Early Cretaceous (e.g., Endress
1986,1987, Friis et a/. 1986, Crane et a/. 1989, Herendeen et
a/. 1993, Brenner 1996). Less is known about their pollination and breeding systems. Chloranthaceae comprise four
genera of which two, Chloranthus with 15species and
Sarcandra with three species, are endemic in lndomalaysia
and Eastern Asia. Both appear to be insect-pollinated,
although only Chloranthus has been studied in the field and
greenhouse (Ma et a/. 1997, Luo and Li 1999, Wang et a/.
1999, Balthazar and Endress 1999, see Endress 2001 for a
recent summary). Phylogenetically, Sarcandra and Chloranthus are sistergroups (Qiu et al. 1999) and derived relative
to the other two genera, Hedyosmum and Ascarha, which
likely are wind-pollinated (Endress 1987, 2001).
Mating systems in Chloranthaceae have been examined in
the greenhouse for Sarcandra chloranthoides, S. glabra, and
Chloranthus spicatus (Balthazar and Endress 1999), and in
the field for C. fortunei, C. henwi, C.holostegius, and C.
serratus (Ma et al. 1997, Luo and Li 1999, Wang et a/. 1999).
With the exception of C. spicatus, all were found to be self-
*
Corresponding author: takahash@ cc.gifu-u.ac.jp
compatible. Here we report the first field data on the
pollination and mating system of S. glabra.
Materials and Methods
Field investigations were conducted at Aka0 (40m alt.),
Takatomi-cho, Yamagata-gun, Gifu Prefecture, and at
Uruno (50 m alt.), Kozagawa-cho, Higashimuro-gun, Wakayama Prefecture. The flowering process was observed in
thirty flowers at the Aka0 site in July of 1997. Insects visits
were recorded at the Aka0 site for about 130 hours and at
the Uruno site for about 20 hours. Each inflorescence
usually consists of four spikes (cf. Balthazar and Endress
1999), and each was used for only one pollination experiment. Experimental crossings and selfings were performed
on female-stage flowers and bisexual-stage flowers from the
middle of the spikes. Pollen for cross-pollination was
collected from newly opened anthers on plants more than 10
m away. Pollen for self-pollination of female-stage flowers
was collected from newly opened anthers on the same
inflorescence. Pollen for self-pollination of flowers in the
bisexual stage came from the stamen of the same flower.
Anther dehiscence could usually be predicted based on
anther color (Results) and flower position because there is an
almost regular progression in anther opening from the apical
flowers of a spike downwards. This regular progression of
spike flowering enabled us to emasculate flowers just before
they shed their pollen. All flowers used in experimental
crossings and apomixis tests were emasculated. With the
exception of open-pollinated controls, inflorescences were
bagged with I-mm or finer mesh polyethylene screens before
their stigmas became receptive. Bags were removed when
stigmas had dried up.
The average number of pollen grains per flower was
calculated by placing mature anthers on glass slides and
flushing pollen grains from the thecae with about 0.3 ml of
70% ethanol. After removal of the empty anther and evaporation of the ethanol, grains were immersed in a 1 : 1 mixture
of glycerin and water with aniline blue and counted under a
microscope. Ovules in the same flowers were counted
under a binocular.
Voucher specimens of Sarcandra glabra have been deposited in the herbarium of Gifu University, which also
424
Y. Tosaki et al.
Figs. 1-6. Sarcandm glabra flowers and their insect visitors, bar=l mm. 1. A female-stage flower, showing
the single stamen to the left and the receptive stigma to the upper right. 2. Ladybird beetle (Coccinellidae) visiting male-stage flowers. 3. Alticinae beetle on bisexual-stage flowers. 4. Pseudomordellistena kaguyahime beetle on female-stage flowers. 5. Glipostenoda rosseola beetle on bisexual-stage
flowers. 6. A cerambycid beetle on female-stage flowers.
Pollination of Sacandra glabra
425
I
.
1
Figs. 7-10. Insects visiting Sarcandra glabra flowers, b a r 4 mm. 7 and 8. Pentatomid hemipterans visiting
the flowers. 9. A syrphid fly visiting female-stage flowers. 10. A Lasiogbssum bee visiting malestage flowers.
houses some of the insects collected. Additional insect
vouchers have been deposited in the Osaka Museum of
Natural History.
Results
Flowering in Sarcandra glabra
Each spike of Sarcandra glabra has 6-14 flowers, and
flowering normally proceeds from the top of a spike downwards over two to three days. The carpels are green, and
the crenate stigmas become moist several days before
anther dehiscence (Fig. 1). Mature but still indehisced stamens have a creamish white connective and cream thecae,
which turn orange or reddish-brown upon opening (Figs. 2,4,
10). Anther dehiscence occurs several days after the stigmas become receptive, mainly in the early morning (6-8
a.m.), but occasionally also throughout the day. Thecae are
emptied within a few days, and the stamens fall off after 2 to
8 days. Flowers emit a weak fragrance just prior to anther
dehiscence and a stronger fragrance thereafter. Small
droplets of liquid were occasionally observed on carpels and
inflorescence axes.
Insect visitors
Table 1 lists the insects collected on the flowers of Sarcandra glabra. Small, between 1.5 and 6 mm long, beetles (Figs.
flies (Fig. 9),bees (Fig. lo), and
2-6), hemiptera (Figs. 7,8),
rarely ants visited inflorescences and flowers just prior to
anther dehiscence and during the two days after dehiscence. The beetles probed carpels and spike axes, apparently to take up the droplets secreted there, and they also
foraged for pollen in older flowers. They often touched the
stigmas, carried numerous pollen grains on their bodies, and
frequently switch between plants. The Ceratina, Lasioglossum, and Hylaeus bees foraged for pollen in bisexual-stage
flowers and also touched the stigmas while moving on and
Y. Tosaki et a/.
426
Table 2. Experimental pollination in Sarcandra glabra
Table 1. Insects foraging on the flowers of Sarcandra glabra
Insects
Foraging
objects"
Glipostenoda rosseola Marseul
Pseudomordellistena kaguyahime Nomura et Kato
1 sp.
Diptera
Anthomyiidae
1 sp.
Syrphidae
Apidae
Ceratina japonica Cockerell
Colletidae
Hylaeus floralis Smith
Halictidae
Lasioglmsum sp.
1)
F
B
F
B
Self-pollination
p, 0
Bagged emasculated flowers
P. 0
Bagged intact flowers
Open pollination
Fruits
Fruit set
l)
-
-
22
13
36
6
20
13
a 4 2 9
50
0
40
13
86
42
59.1
16.7
65.0
34.5
0
32.5
48.4
F, female stage; 6, bisexual stage.
p, 0
p, 0
P. 0
P. 0
3 SPP.
Hemiptera
Pentatomidae
Eysarcoris guniger Thunberg
1 sp.
Hymenoptera
Formicidae
Camponotus yamaokai Terayama et Satoh
Crematogaster brunnea teranishii Santschi
Flower
("0)
Cross-pollination
Coleoptera
Cerambycidae
1 sp.
Chrysomllidae
1 sp.
Coccinellidae
1 sp.
MordelIidae
Flower
stage,,
Treatment
0
0
p, 0
P
P
P, foraging for pollen; 0, probing carpel surface.
between inflorescences. They carried large pollen loads.
The hemiptera visited female- and bisexual-stage flowers
and generally behaved much like the beetles except that
they did not touch the stigmas as frequently. Four species
of anthomyiid and syrphid flies foraged for pollen or pr6bed
the carpels (apparently for the small droplets of liquid sometimes secreted there), but they rarely touched the stigmas.
There were no differences in the visitor spectra between the
Aka0 and the Uruno sites.
Breeding experiments
Results of the breeding experiments are given in Table 2.
Fruit set after experimental crossing and selfing of femalestage flowers was not significantly different (59 and 65%,
respectively, chi-square=0.15, df=l, not significant). In
bisexual-stage flowers, however, selfing resulted in higher
fruit set than outcrossing (35 vs. 17%, chi-square=3.89, df=
1, P<0.05). Fruit set in female-stage flowers was significantly higher than fruit set in bisexual-stage flowers, both in
crossed and in selfed flowers (chi-square=11.16 for crosspollinated flowers, df=l, P< 0.005; chi-square=6.23 for
self-pollinated flowers, df=l, P<0.025). None of the emasculated flowers produced fruit, while bagged inflorescences
had a fruit set of 33%. Of the open-pollinated flowers, 48%
set fruit, which was not significantly different from experimentally crossed female-stage flowers (chi-square=0.74,
df=l) and marginally higher than the fruit set in bagged
inflorescences (chi-square=2.96 df=l, P between 0.1 and
0.05).
Pollen number
The average number of pollen grains in a stamen of
Sarcandra g/abra was 22.6X102(n=lO, range 41X102to 11X
lo2;SD 7.35X102). Flowers contained one ovule, and the
pollen/ovule ratio therefore was the same as the pollen
number.
Discussion
Fruit set in female-stage selfed or outcrossed Sarcandra
glabra flowers was not significantly different, indicating that
S.glabra is self-compatible. A study of two plants cultivated in a greenhouse at the University of Zurich (Balthazar
and Endress 1999) found that fruit set after selfing was
between 6 and 33% (crossings could not be carried out).
Based on stigma receptivity tests with 5% H202 and with
KMn04,Balthazar and Endress suggested that stigmas were
receptive several days prior to anther dehiscence and
remained receptive throughout the bisexual phase. Our
results, however, indicate that stigma receptivity is significantly higher in female-stage flowers than it is in bisexualstage flowers (59 vs. 17% in outcrossed flowers and 65 vs.
35% in selfed flowers).
Bagged inflorescences that did not receive insect visits
still had 33% fruit Set, probably due to pollen from apical
(older) flowers falling onto stigmas of the lower (younger)
flowers of an inflorescence as also observed by Balthazar
and Endress (1999). Thecae not visited by insects contain a
lot of pollen, and we observed grains falling down when
anthers received mechanical stimulation, for example, from
strong wind.
Based on the bisexual flowers, sticky pollen, and short
single stamen, Endress (1986,1987) suggested that Sarcandra
Pollination of Sarcandra glabra
was insect-pollinated, most likely by beetles. This first
study of the natural pollination of a species of Sarcandra
shows that the flowers are visited by a range of insects,
including beetles, bees, pentatomid hemiptera, and flies, with
at least the former three groups regularly touching the
stigmas. We also found that, in addition to pollen, beetles,
hemiptera, and flies apparently take up minute droplets from
the carpels and inflorescence axes. In the greenhouse,
Balthazar and Endress did not observe droplets on carpels or
,spike axes of S. chloranthoides. However, they found that
bract apices secreted droplets through stomata (their Fig.
5a-d). In S. glabra, we did not see droplets on the bracts (at
a magnification of 150 times) nor did we find stomata on the
carpels that might have secreted the minute droplets.
We thank Dr. K. Yamauchi of Gifu University and Drs. S.
Shiyake and S. Fujii of the Osaka Museum of Natural History
for the identification of the insects, Dr. H. Takasu of Wakayama University for advice on the selection of study sites,
and Dr. Peter Endress for comments on the manuscript.
This study was supported by a Grant-in-Aid for Scientific
Research from the Japan Society for the Promotion of
Science (10640680).
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(Received June 8, 2007; accepted September IS, 2001)