Table Of Content植物研究雑誌
J.Jpn.Bot.
82:20–28(2007)
Inferring the Origin of Potamogeton ×inbaensis (Potamogetonaceae)
Using Nuclear and Chloroplast DNA Sequences
Yu ITOa,＊, Norio TANAKAb and Koichi UEHARAa
aLaboratoryofPlantMorphology,FacultyofHorticulture,ChibaUniversity,
Matsudo,Chiba,271-8510JAPAN;
*PresentAddress:BotanicalGardens,GraduateSchoolofScience,TheUniversityofTokyo,
Bunkyo-ku,Tokyo,112-0001JAPAN
bTsukubaBotanicalGarden,NationalScienceMuseum,Tsukuba,Ibaraki,305-0005JAPAN
(ReceivedonAugust21,2006)
Many hybrid taxa have been described in Potamogeton. These hybrids can usually
be recognized by morphological intermediacy between parent species but in some cases
recognition is difficult due to extensive morphological variation. Potamogeton
×inbaensis Kadono which was reported as a hybrid between P. lucens L. subsp. sinicus
(Migo) H. Hara var. teganumensis (Makino) H. Hara and P. wrightii Morong, is one of
them. In this study nuclear and chloroplast DNA sequence confirmed this report and
inferred P. wrightii as the maternal parent of the hybrid. Potamogeton×inbaensis was
also found together with both parents a few years ago in artificial ponds near Inbanuma
Lake, but no hybrid plants from opposite parental pairs were recognized. Considering
geographic distance P.×inbaensis is inferred to have undergone hybridization events
independently in Inbanuma Lake and in Oitoike Pond. Morphological analysis showed
that leaf morphological characters partially overlap between P.×inbaensis and both of
theparentaltaxawhichsuggeststhatidentificationbasedonleafmorphologyneedscare-
ful examination and that molecular analysis is a more useful tool for recognition of
hybrids.
Key words: atpB-rbcL, hybrid, ITS, morphology, Potamogeton.
The genus Potamogeton L. (Potamo- et al. 1998b, King et al. 2001, Fant et al.
getonaceae) is one of the largest genera of 2001a, 2001b, 2003, 2005, Iida and Kadono
aquatic plants and is distributed in fresh 2002, Kaplan et al. 2002, Fant and Preston
waterareasoftheworld(Preston1995,Cook 2004, Kaplan and Fehrer 2004, Kaplan and
1996, Wiegleb and Kaplan 1998). It is well Wolff 2004, Whittall et al. 2004) investi-
known that the genus shows extensive mor- gated the hybrid species and inferred their
phological variation at species level and origin. Of these Kaplan and Fehrer (2004)
intraspecific level (Kaplan 2002). In the reported that nuclear ribosomal (nr) DNA
most recent monograph of the genus, 69 spe- markers are a useful tool to identify
cies and 50 confirmed hybrids are recog- Potamogeton hybrids.
nized (Wiegleb and Kaplan 1998). Several In the flora of aquatic plants in Japan, 18
studies based on morphology (Preston et al. species and 9 hybrids of the genus were
1998a, Kaplan 2001) or based on both mor- recognized (Kadono 1994). One putative
phological and molecular analyses (e. g., hybrid Potamogeton×inbaensis Kadono,
Hollingsworth et al. 1995, 1996, Preston which is not recognized in the monograph of
—20—
February2007 JournalofJapaneseBotanyVol.82No.1 21
Wiegleb and Kaplan (1998), was originally Kaplan and Fehrer (2004) and Iida et al.
reported from Inbanuma Lake (Kadono (2004). We collected morphologically typi-
1983) and is known to be distributed in the cal plants of each taxon as standard and
Inbanuma and Teganuma Lakes of Chiba examined their genotypes. Then we com-
prefecture and disjunctly in Kita-Kyushu-shi pared the genotypes of plants sampled from
of Fukuoka Prefecture (Kadono 1994). As the artificial ponds to the standard ones. In
the putative hybrid is male sterile and shows addition we examined the morphological
an intermediate feature in length of petiole characters of the plants to consider circum-
and leaf size between P. lucens L. subsp. scription of the taxa.
sinicus (Migo) H. Hara var. teganumensis
(Makino) H. Hara and P. wrightii Morong Materials and Methods
(Kadono 1983), it is considered to be their Taxon sampling–We collected morphologi-
hybrid. One parent species P. lucens subsp. cally typical plants as standard of each taxon
sinicus var. teganumensis is an endangered todeterminemolecularmarkers;oneplantof
speciesanditsdistributionislimitedtoafew P. lucens subsp. sinicus var. teganumensis
localities in Japan (Kadono 1994 Environ- from Oitoike Pond, one of P. wrightii from
ment Agency of Japan 2000). The other, P. Namiki and three of P.×inbaensis from
wrightii, iswidely distributed in East Asia, Inbanuma Lake the type locality and Oitoike
India, Southeast Asian islands and the Pond (Table 1, Fig. 1). In addition we col-
Pacificarea(Wiegleb1990b).Theseputative lected a total of 20 Potamogeton plants from
parentspeciesareknowntobeclearlydistin- Pond1 and 2 in 2000 and from 3 in 2000 and
guished based on nucleotide sequences of 2003, respectively (Table 1, Fig. 1). Fresh
chloroplast (cp) DNA (Iida et al. 2004) as leaves were stored at –80ºC for molecular
well as leaf morphology (Kadono 1983). analysis. Their voucher specimens were de-
Recently for conservation of aquatic posited in the Herbarium of The National
plants three artificial ponds (referred to as Science Museum (TNS) and some plants
Pond 1, 2 and 3 in this study) were made on were transplanted to the Tsukuba Botanical
the reclaimed land of Teganuma Lake in Garden, The National Science Museum.
19971998and2002respectively(Fig.1).As
was reported in Momohara et al. (2001) DNA analysis–DNA extraction and PCR
several aquatic plants that were germinated amplification: Total DNA was extracted
from buried seeds in the lake sediments were from frozen leaf tissue and purified follow-
observed in these ponds. Among them P. ing the method of Tanaka et al (2003). First,
lucens subsp. sinicus var. teganumensis and for the standard plants, internal transcribed
P. wrightii were found together with their spacer (ITS) region of nrDNA and the
putative hybrid. However, contrary to the intergenic region between atpB and rbcL
Kadono’s (1983) suggestion, it is difficult to genes (atpB - rbcL) ofcpDNA were ampli-
criticallydistinguishthesethreetaxabecause fiedbythepolymerasechainreaction(PCR).
of extensive morphological variation. ITSregionwasamplifiedusingprimersITS4
In the present study we aimed to identify and ITS5 of Baldwin (1992) and atpB - rbcL
plants from the three artificial ponds and to region using primers atpB2F of Manen et al.
infer the origin of P.×inbanensis based on (1994) and rbcL2R [5’ - CAA CAC TTG
both morphological and molecular analyses. CTT TAG TCT CT - 3’] newly designed for
First we determined molecular markers that the present study. The PCR reaction mixture
can distinguish each taxon using nrDNA and consisted of 1.0 unit of ExTaq DNA
cpDNA sequences in considering insights by polymerase (TaKaRa Bio, Ohtsu, Shiga,
22 植物研究雑誌 第82巻 第1号 平成19年2月
Table1. Locationof Potamogetonplantmaterialandresultsofmolecularanalysis
DDBJ DDBJ
Numberof Voucher
Species Locality ITS Accession cpDNA Accession
individuals specimen
number number
P.lucenssubsp.lucensvar.teganumensis
OitoikePond,FukuokaPrefecture(Control) 1 TNS9525969 L AB206990 L AB206987
ITS cp
Teganumaartificialpond1,ChibaPref.(POND1) 1 TNS9525970 L L
ITS cp
Teganumaartificialpond2,ChibaPref.(POND2) 1 TNS9525971 L L
ITS cp
Teganumaartificialpond3,ChibaPref.(POND3) 9 TNS9525973-TNS9525981 L L
ITS cp
P.wrightii
Namiki,IbarakiPrefecture(Control) 1 TNS9525993 W AB206991 W AB206988
ITS cp
Teganumaartificialpond1,ChibaPref.(POND1) 1 TNS9525995 W W
ITS cp
Teganumaartificialpond2,ChibaPref.(POND2) 2 TNS9525996-TNS9525997 W W
ITS cp
Teganumaartificialpond3,ChibaPref.(POND3) 3 TNS9525999-TNS9526001 W W
ITS cp
P.(cid:1)inbaensis
LakeInbanuma,ChibaPrefecture(Control) 1 TNS9525987 LW W
ITS cp
OitoikePond,FukuokaPrefecture(Control) 2 TNS9525988-TNS9525989 LW W
ITS cp
Teganumaartificialpond1,ChibaPref.(POND1) 1 TNS9525990 LW W
ITS cp
Teganumaartificialpond2,ChibaPref.(POND2) 1 TNS9525991 LW W
ITS cp
Teganumaartificialpond3,ChibaPref.(POND3) 1 TNS9525992 LW W
ITS cp
Fig.1. Sampling locations. Shaded areas show the reclaimed land near
TeganumaLake.
February2007 JournalofJapaneseBotanyVol.82No.1 23
Japan), 1 µL of 10 (cid:1)ExTaq buffer (10 mM for samples including heterogeneous
Tris-HCl [pH 8.3], 50 mM KCl, 1.5 mM sequences in ITS region sequencing primers
MgCl ), 0.8 µL of 0.2 mM dNTP solution, ITS3 of Baldwin (1992) and ITS3_inba2
2
0.5 µL of each 10 pM primer and 10–30 ng [5’ - GTG GAG ATT GAC CCT CCA TT -
of genomic DNA in a total volume of 11 µL. 3’] newly designed for the present study
PCR cycling conditions for amplification of wereusedtoseparateallelesfromPCRprod-
ITSregionandatpB-rbcLregionwere96°C ucts without cloning method.
for 2 min then 35 cycles of 96°C for 45 sec,
52°C for 30 sec, 72°C for 1 min, and finally Morphological analysis–Kadono (1983)
72°C for 5 min. used leaf morphological characters to distin-
guish P. lucens subsp. sinicus var. teganu-
Direct sequencing and cloning for the mensis, P. wrightii and P.×inbaensis. We
standard samples–Nucleotide sequences of measured length of petiole, and width and
PCR products were determined by the direct length of leaf lamina for all collected sam-
sequencing or cloning methods. Template ples (Fig. 2). The ratio of length/width of
DNA fragments were amplified using the leaf lamina was used to evaluate the leaf
ABI PRISM Big Dye Terminator v 3.1 shape.
(Applied Biosystems, Foster, California, Kadono (1983) also reported the number
USA) with the same primers as those used of vascular bundles and its arrangement in
for PCR. DNA sequencing was performed the stem stele for the three taxa. Wiegleb
using an ABI PRISM 3100 (Applied (1990a) classified the Potamogeton species
Biosystems). The resultant electopherograms based on the shape of the stem stele. We
of direct sequencing for the ITS region of examined the shape of the transverse section
plants of P.×inbaensis showed superim- of stem stele using transplanted plants (Fig.
posed waves at the same sites for both com- 3). Internodes from each shoot were sliced
plementary strands. These products were byrazorandtransversesectionswerestained
ligated into lacZ sites of pGEM-T Easy in 0.05 (cid:1)toluidine blue for a few minutes.
Vector (Promega, Madison, Wisconsin, Stained samples were observed under a
USA) using Ligation High (TOYOBO, microscope.
Osaka, Japan) and then the recombinant
plasmids were transformed into JM109 com- Results and Discussion
petent cell (Promega). Ninety-six clones per Molecular markers to identify taxa and
sample were picked from clones grown on hybrid origin–From ITS sequences of the
Luria-Bertani agar plates containing ampicil- standard samples, two sequence types were
lin. Plasmids including the target region distinguished. These types differed from
wereusedastemplateDNAinPCRandtheir each other at a total 30 sites; 27 substitutions
nucleotide sequences were determined. and three indels (Table 2). Each standard
plant of P. lucens subsp. sinicus var.
Sequencing for samples from the artificial teganumensis and P. wrightii has a specific
ponds–Based on results for the standard sequence, L type (644 bp) and W type
ITS ITS
plants genotypes of ITS and cpDNA for (642 bp), respectively. The standard samples
plants, from the artificial ponds were deter- of P.×inbaensis include L and W types
ITS ITS
mined. Nucleotide sequencing of ITS and together so that it showed heterozygosity
atpB - rbcL regions of samples from the arti- (LW type).
ITS
ficial ponds were determined using PCR and From atpB - rbcL sequences of the stan-
direct sequencing methods. On sequencing dard samples two sequence types were
24 植物研究雑誌 第82巻 第1号 平成19年2月
Fig.2. Comparisonofleafmorphologicalcharactersi.e.,lengthofpetioleandlength/
width of leaf lamina that have been used as identification characters since Kadono
(1983).Thethreetaxawereidentifiedbasedonmoleculardata.Round,squareand
triangle symbols indicate Potamageton lucens subsp. sinicus var. teganumens, P.
wrightiiandP.×inbaensis,respectively.Barsindicatemaximumandminimumval-
uesineachplants.
found. These types were distinguished by considering the maternal inheritance of the
one substitution and two indels (Table 3). chloroplast genome, sharing of W types
CP
The standard sample of P. lucens subsp. suggested that P. wrightii is the maternal
sinicus var. teganumensis has a specific parent of the standard samples of P.
sequence L type (779 bp) but those of P. ×inbaensis and P. lucens subsp. sinicus var.
CP
wrightii and P.×inbaensis shared an identi- teganumensis is the paternal parent.
cal W type (783 bp). No P.×inbaensis
CP
plants with L type were observed. Genotyping of plants from the artificial
CP
By combining the sequence types of ITS ponds–As it has been reported that maternal
and cpDNA, three taxa are likely to be dis- or paternal species are not always fixed for
tinguished based on genotypes. Potamageton other Potamogeton hybrid taxa (Fant et al.
lucens subsp. sinicus var. teganumensis, P. 2003, 2005), we need to analyze more sam-
wrightii and P.×inbaensis showed L /L ples to clarify the process of hybridization
ITS CP
genotype, W /W genotype and LW /W occurring P.×inbaensis.
ITS CP ITS CP
genotype, respectively. The LW /W geno- Among20plantsfromtheartificialponds,
ITS CP
typeofthestandardsamplesofP.×inbaensis L and W types in ITS and L and W
ITS ITS CP CP
supports the view that it originated from a types in atpB - rbcL were detected. Of these,
cross between P. lucens subsp. sinicus var. 11 plants showed the L /L genotype, six
ITS CP
teganumensis and P. wrightii. Inaddition, plantstheW /W genotypeandthreeplants
ITS CP
February2007 JournalofJapaneseBotanyVol.82No.1 25
Fig.3. StemtransversesectionofthethreetaxaofPotamagetonshowingthepartofstemstele.A,
C:Oblongtypewiththreevascularbundles.B,D:Eightbundletype.A.P.lucenssubsp.sinicus
var. teganumens from Pond 3 (TNS 9525975) B. P. wrightii from Pond 3 (TNS 9526000). C.
P.×inbaensisfromOitoikePond(TNS9525989)D.P.×inbaensisfromInbanumaLake(TNS
9525987).Scalebar(cid:1)100µm.
Table 2. Comparison of the ITS sequences of thePotamogeton individuals examined. Only the sites that differed
amongtaxaareshown.217and418areonebasegaps,613–614isatwo-basegap
1 1 2 2 2 4 4 4 4 4 4 4 4 5 5 5 5 5 5 66 6 6 6
Position 1 1 2 3 4 5 8 5 8 1 1 2 0 0 1 1 2 8 9 9 1 3 4 5 5 9 11 1 2 3
1 4 1 7 8 5 3 5 6 4 7 7 1 7 7 8 4 9 0 6 7 0 8 5 6 5 34 9 7 8
L C T C G G T T G A C – G G A C C C T C A A T C C C C TA C C A
Type ITS
W T G A C T A C T T T T A C C T – T A T G T G T T T T –– T T T
ITS
Table 3. Comparison of the atpB-rbcL sequences from the
Potamogetonindividualsexamined.Onlythesitesthatdif-
feredamongtaxaareshown.179(cid:514)186isaneight-basegap,
375(cid:514)378isafour-basegap
1 1 1 1 1 1 1 1 2 3 3 3 3
Position 7 8 8 8 8 8 8 8 7 7 7 7 7
9 0 1 2 3 4 5 6 8 5 6 7 8
L – – – – – – – – T A T T T
Type cp
TW T C A T T C A A C – – – –
cp
26 植物研究雑誌 第82巻 第1号 平成19年2月
the LW /W genotype. No plants with P. wrightii had the eight-bundle type (Fig.
ITS CP
LW /L type were observed. Based on the 3).However,oneplantofP.×inbaensisfrom
ITS CP
results for the standard samples plants with Inbanuma Lake had the oblong lamina with
L /L genotype, those with W /W geno- three vascular bundles while those from
ITS CP ITS CP
type and those with LW /W genotype other areas, including the artificial ponds,
ITS CP
were identified as P. lucens subsp. sinicus have the eight-bundle type (Fig. 3).
var. teganumensis, P. wrightii and P.
×inbaensis, respectively (Table 1). In all We are grateful to Dr. Jin Murata, Dr.
three ponds the three genotypes were found Tetsuo Ohi-Toma and Dr. Zdenek Kaplan
which indicated that three Potamogeton taxa for their critical comments, to Dr. Eisho
occur together. Nishino for his help and advice of anatomi-
Potamogeton×inbaensis with LW /W cal techniques, to Dr. Arata Momohara, Dr.
ITS CP
observed in the artificial ponds may have Norio Hayashi, Ms. Mutsuko Oono and the
originatedfromburiedseedsinthelakesedi- Mashijimi-Gashamoku-no-Kai for their help
ments or newly produced by crossing in situ in sample collection.
between P. lucens subsp. sinicus var.
teganumensis and P. wrightii. Because the References
three artificial ponds are quite recent the Baldwin B. G. 1992. Phylogenetic utility of the inter-
former hypothesis seems to be reasonable. nal transcribed spacers of nuclear ribosomal DNA
It is reported that multiple hybridization in plants: An example from the compositae. Mol.
Phylogenet.Evol. 1(1):3–16.
events have occurred in some Potamogeton
Cook C. D. K. 1996. Aquatic plant book. SPB
hybrids (Fant et al. 2003, 2005). In our case,
AcademicPublishingAmsterdam.
considering the very long geographic Environment Agency of Japan. 2000. Threatened
distance between the localities of P. Wildlife of Japan-Red Data Book 2nd ed.–Vol. 8
×inbaensis, hybridization events are sup- Vascular Plants. 189pp. Japan Wildlife Research
Center,Tokyo(inJapanese).
posed to have occurred independently in
Fant J. B., Kamau E. M. and Preston C. D. 2003.
Inbanuma Lake, a type locality of P.
Chloroplastevidenceforthemultipleoriginsofthe
×inbaensis, and separately in Oitoike Pond.
hybridPotamogeton×sudermanicusHagstr.Aquat.
Bot.75(4):351–356.
Assessment of morphological characters– , and 2005.Chloroplastevidenceforthe
We assessed morphological variation of the multiple origins of the hybrid Potamogeton
×fluitans.Aquat.Bot. 83:154–160.
plants identified by the molecular markers
and Preston C. D. 2004. Genetic structure and
(Fig. 2). Potamogeton lucens subsp. sinicus
morphological variation of British populations of
var. teganumensis have shorter petioles and thehybridPotamogeton×salicifolius.Bot.J.Linn.
wider leaves than those of P. wrightii and Soc.144:99–111.
these two species are distinguished from , andBarrettJ.A.2001a.Isozymeevidence
for the origin of Potamogeton×sudermanicus as a
each other by petiole length, although these
hybrid between P. acutifolius and P. berchtoldii.
taxa showed extensive morphological varia-
Aquat.Bot. 71(3):199–208.
tion even within a single individual.
, and 2001b. Isozyme evidence of the
Morphological variation of P.×inbaensis parental origin and possible fertility of the hybrid
shows intermediate features and partly Potamogeton×fluitans Roth. Plant Syst. Evol.
overlapps with both of the parental species. 229:45–57.
Hollingsworth P. M., Preston C. D. and Gornall R. J.
For the characteristic of stem stele,
1995. Isozyme evidence for hybridization between
Wiegleb (1990a) suggested that P. lucens
Potamogeton natans and P. nodosus (Potamo-
subsp. sinicus var. teganumensis had the ob- getonaceae) in Britain. Bot. J. Linnean Soc. 117:
longlaminaswiththreevascularbundlesand 59–69.
February2007 JournalofJapaneseBotanyVol.82No.1 27
, and 1996. Isozyme evidence for the getonaceae)inBritain.Bot.J.Linn.Soc.135:67–
parentage and multiple origins of Potamogeton 70.
×suecicus (P. pectinatus×P. filiformis Potamo- Manen J. F., Natali A. and Ehrendorfer F. 1994.
getonaceae).PlantSyst.Evol. 202:219-232. PhylogenyofRubiaceae-Rubieaeinferredfromthe
IidaS.andKadonoY.2002.Geneticdiversityandori- sequenceofacpDNAintergeneregion.PlantSyst.
gin of Potamogeton anguillanus (Potamogetona- Evol.190:195–221.
ceae) in Lake Biwa Japan. J. Plant Res. 115: 11– Momohara A., Uehara K., Fujiki T. and Tanaka N.
16. 2001.Distributionandpreservationofseedbankin
, Kosuge K. and Kadono Y. 2004. Molecular lake sediment of Teganuma Chiba Central Japan.
phylogeny of Japanese Potamogeton species in Ann.Tsukuba.BotGard. 20:1–9.
light of noncoding chloroplast sequences. Aquat. Preston C. D. 1995. Pondweeds of Great Britain and
Bot.80(2):115–127. Ireland. Botanical Society of the British Isles
Kadono Y. 1983. New hybrids of Potamogeton from London.
Lake Inba-numa Chiba Prefecture. Acta Phytotax. , Bailey J. P. and Hollingsworth P. M. 1998a. A
Geobot.34:51–54(inJapanese). reassessment of the hybrid Potamogeton
1994. Aquatic plants of Japan. Bun-ichi Sogo ×gessnacensis G. Fisch. (P. natans × P. polygoni-
ShuppanTokyo(inJapanese). folius Potamogetonaceae) in Britain. Watsonia 22:
KaplanZ.2001.Potamogeton×fluitans(P.natans×P. 61–68.
lucens) inthe Czech Republic. I. Morphology and , Hollingsworth P. H. and Gornall R. J. 1998b.
anatomy.Preslia 73:333–340. Potamogeton pectinatus L.×P. vaginatus Turcz.
2002. Phenotypic plasticity in Potamogeton (P.×bottnicusHagstr.)anewlyidentifiedhybridin
(Potamogetonaceae). Folia Geobot. 37(2): 141– theBritishIsles.Watsonia 22:69–82.
170. Tanaka N., Kuo J., Oomori Y., Nakaoka M. and Aioi
and Fehrer J. 2004. Evidence for the hybrid ori- K. 2003. Phylogenetic relationships in the genera
ginofPotamogeton×cooperi(Potamogetonaceae): Zostera and Heterozostera (Zosteraceae) based on
traditional morphology-based taxonomy and matKsequencedata.J.PlantRes. 116:273–279.
molecular techniques in concert Folia Geobot. 39: Whittall J. B., Hellquist C. B., Schneider E. L. and
431–453. Hodges S. A. 2004. Cryptic species in an endan-
and Wolff P. 2004. A morphological anatomical gered pondweed community (Potamogeton,
and isozyme study of Potamogeton×schreberi: Potamogetonaceae) revealed by AFLP markers.
confirmation of its recent occurrence in Germany Am.J.Bot. 91:2022–2029.
and first documented record in France. Preslia 76: WieglebG.1990a.Theimportanceofstemanatomical
141–161. characters for systematics of the genus
, Plackova I. and Stepanek J. 2002. Potamogeton PotamogetonL.Flora 184:197–208.
×fluitans (P. natans×P. lucens) inthe Czech 1990b. A redescription of Potamogeton wrightii
Republic. II. Isozyme analysis. Preslia 74: 187– Morong.PlantSyst.Evol. 170:53–70.
195. andKaplanZ.1998.Anaccountofthespeciesof
KingR.A.,GornallR.J.,PrestonC.D.andCroftJ.M. Potamogeton L. (Potamogetonaceae). Folia
2001. Molecular confirmation of Potamogeton Geobot.33:241–316.
×bottnicus (P. pectinatus×P. vaginatus Potamo-
伊藤 優a, *, 田中法生b, 上原浩一a：核DNAお
よび葉緑体DNA塩基配列を用いたPotamogeton
×inbaensis (ヒルムシロ科) の起源推定 ×inbaensisKadonoもその一つである. 本研究では,
ヒルムシロ属には, 多くの種間雑種が認識され 核DNAと葉緑体DNAの塩基配列を用いて解析
ている. これら雑種は一般に両親種の中間的形質 した結果, インバモがササバモを母親とし, ガシャ
を示すが, ヒルムシロ属では特に形態形質の変異 モクを父親とする組み合わせで生じた雑種である
が大きいために, 両親種の推定や両親種からの識 と推定した. 近年増設された印旛沼近くの人工池
別が容易ではないものが多い. 外部形態形質, 特 でも両親種とともにインバモ3個体が確認された
に葉形態形質に基づいてガシャモクとササバモの が, それらもすべてササバモを母親とする組み合
雑種として報告されたインバモ Potamogeton わせで生じていた. 地理的距離を考慮すると, 雑
28 植物研究雑誌 第82巻 第1号 平成19年2月
種形成は千葉県印旛沼と福岡県お糸池の二ヶ所で 分子遺伝学的情報はより有益な手段であると考え
独立に起こったと推定される. 外部形態形質を比 られる.
較した結果, インバモの葉形態形質は両親種との (a千葉大学園芸学部植物構造学研究室,
間で部分的に重なりが見られ, 形態だけでは認識 *現所属：東京大学大学院
ができない雑種個体があることがわかった. 葉形 理学系研究科附属植物園,
態形質による雑種の識別には注意が必要であり, b国立科学博物館筑波実験植物園)
