Bull. Natl. Mus. Nat. Sci., Ser. B, 43(2), pp. 57–61, May 22, 2017

The Chromosome Numbers ofFour Gesneriaceae Species Native to Japan
Goro Kokubugata1,*and Masatsugu Yokota2
1

Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
2
Laboratory of Ecology and Systematics, Faculty of Science, University of the Ryukyus,
Nishihara, Okinawa 903–0213, Japan*E-mail: gkokubu@kahaku.go.jp(Received 8 February 2017; accepted 22 March 2017)

Abstract Chromosome numbers at mitotic metaphase in four Gesneriaceae species native toJapan were investigated using the aceto-orcein squash method in the present study. The chromosome number was determined as 2n＝32 in Aeschynanthus acuminatus and this is the ﬁrst chromosome number report in this species. In the other three species, the chromosome number was
2n＝20 in Rhynchotechum discolor; 2n＝34 in Opithandra primuloides; and 2n＝40 in Titanotrichum oldhamii.
Key words : chromosome number, Gesneriaceae, Japan, Ryukyu.

Introduction
Gesneriaceae is a middle to large sized plantfamily comprising approximately150–160 genera, and over 3200 species. Its members are distributed primarily in the tropical regions, withsome members extending to the template regions
including Honshu of Japan (Weber and Skog,2007 onward).
According to Yamazaki (1994), nine species
from eight genera of Gesneriaceae are distributedin Japan, and these species are the northernmost
species in each of the genera. Several taxonomicand molecular phylogenetic studies have been
conducted for these Gesneriaceae species inJapan (Yamazaki, 1994; Kokubugata, 2002;
Kokubugata and Peng, 2004; Kokubugata et al.,2011, 2014). However, cytological data on theGesneriaceae species in Japan is still limited;
there are only two reports on Conandron ramondioides, including C. ramondioides var. taiwanensis (Kokubugata and Peng, 2004) and Cytandra cumingii (Kokubugata and Madulid, 2000).

The aim of this study is to investigate chromosome numbers of four Japanese Gesneriaceae
species: Aeschynanthus acuminatus Wall. ex DC,Opithandra primuloides (Miq.) B. L. Burtt,
Rhynchotechum discolor (Maxim.) B. L. Burttvar. discolor and Titanotrichum oldhamii(Hemsl.) Soler. Resulting chromosome counts
will be compared with previous reports on theGesneriaceae Species from different areas, andtaxonomic issues will be discussed.
Materials and Methods
Plant materials
Plants materials of each species were collectedby the authors, and were cultivated in the greenhouse of Tsukuba Botanical Garden, National
Museum of Nature and Science for cytologicalexperiments. Voucher specimens were depositedin the herbarium of National Museum of Natureand Science (TNS) (Table 1).
The genus Aeschynanthus Jack consists ofabout 160 species, mainly distributed from India,

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Goro Kokubugata and Masatsugu Yokota
Table 1.

Collection localities and voucher specimens of Gesneriaceae species in the present cytological study

SpeciesCollection locality

Collection number (Herbarium)

Aeschynanthus acuminatus
Opithandra primuloides
Rhynchotechum discolor
Titanotrichum oldhamii

Japan, Ryukyus, Okinawa, Yaeyama Group, Iriomote Island.
Japan, Shikoku, Kochi, Shimanto.
Japan, Ryukyus, Okinawa, Yaeyama Group, Ishigaki Island.
Japan, Ryukyus, Okinawa, Yaeyama Group, Iriomote Island.

G.Kokubugata11644 (TNS)
G.Kokubugata9463 (TNS)
G.Kokubugata214 (TNS)
G.Kokubugata1346 (TNS)

the southern part of China, throughout Malaysia
to New Guinea and the Solomon Islands (Middleton, 2007). Aeschynanthus acuminatus iswidely distributed from India to Japan (Li andKao, 1998). In Japan, this species was ﬁrst foundin 1973 in Iriomote Island of the Ryukyus Archipelago (hereafter the Ryukyus) (Hatusima,1974). Thereafter, the species had not been foundfor decades, and Kobayashi and Kokubugata(2005) rediscovered the species in a locality near
the original locality reported by Hatusima(1974). To date, no other population of this species has been found in Japan, and thus the species is protected as a critically endangered species (CR) in Japan (Japanese Ministry ofEnvironment, 2015).
The genus Opithandra B. L. Burtt consists of
11 species, and is distributed in the southern partof China (10 species) and Japan (one species)(Wang, 2004). Opithandra primuloides isendemic to Japan proper (Honshu, Shikoku andKyushu), and treated as a threatened species(VU) because of its rare occurrence (JapaneseMinistry of the Environment, 2015).
The genus Rhynchotechum Blume consists of
16 species and primarily occurs in tropical andsubtropical Asia (Wang and Wang, 2000); inJapan one species and two varieties are known:
R. discolor var. discolor and R. discolor var.
incisum (Ohwi) E. Walker. Rhynchotechum discolor var. discolor is distributed in Kyushu andthe Ryukyus of Japan, Taiwan, and the Philippines.
The genus Titanotrichum Soler is monotypicand consists of T. oldhamii, the species distributed in China, Japan and Taiwan (Weber andSkog, 2007 onward). In Japan, this species israrely found on Ishigaki and Iriomote islands of
the Ryukyus, and thus it is treated as a criticallyendangered species (CR) in Japan (JapaneseMinistry of Environment, 2015).
Chromosome observation
Root tips of cultivated accessions were pretreated in 2 mM 8-hydroxyquinoline at 20°C for
4 h, and ﬁxed in 45% acetic acid for 10 sec. They
were macerated in a mixture of 1 N hydrochloric
acid and 45% acetic acid at 60°C for 5 sec., andwere stained in 2% aceto-orcein on glass slides at
20°C for 3 hrs. The standard squash method wasapplied to make well-spread chromosomes at
mitotic metaphase.
Results and Discussion
Aeschynanthus acuminatus Wall. ex DC (Fig. 1A)
One plant of A. acuminatus from Iriomote
Island of the Ryukyus showed a chromosome
number of 2n ＝32 (Fig. 1B). This is the ﬁrst
chromosome-number report in the species.
Möller and Kiehn (2004) suggested three basic
chromosome numbers of x＝14, 15 and 16 forthe genus Aeschynanthus, and the present chromosome number in agreement with the idea thatx＝16 is the most common in the genus
Aeschynanthus (Möller and Kiehn, 2004).
Opithandra primuloides (Miq.) B.L.Burtt (Fig.
1C)
One plant of Opithandra primuloides wasinvestigated and showed a chromosome numberof 2n＝34 (Fig. 1D). This agrees with the reports
by Fussell (1958) and Ratter (1963). However,collection locality of plant materials was notindicated in their reports.
Concerning the taxonomy, the species was ﬁrst
described as Boea primuloides Miq. based on atype specimen collected from Japan (Miquel,Chromosome Numbers of Four Gesneriaceae Specie

59

Fig. 1. Plants and chromosomes at mitotic metaphase of four Gesneriaceae species. A, C, E and G. Plants. B, D, Fand H. Somatic chromosomes at mitotic metaphase. A and B. Aeschynanthus acuminatus (G.Kokubugata11644).
C and D. Opithandra primuloides (G.Kokubugata9463). E and F. Rhynchotechum discolor var. discolor(G.Kokubugata214). G and H. Titanotrichum oldhamii (G.Kokubugata1346). In A, C and G, the ﬂowers were
photographed in Tsukuba Botanical Garden. Bar indicates 5 μm for B, D, F and H.

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Goro Kokubugata and Masatsugu Yokota

1867). Thereafter, the species was transferredand named Oreocharis primuloides (Miq.)
Benth. et Hook.f. ex Clarke (Clarke, 1883); andthen Opithandra primuloides by Burtt (1956) as
the genus Opithandra was established. A recent
molecular phylogenetic study revealed thatOpithandra primuloides was included in a cladeof Oreocharis sensu lato, and supported the taxonomic treatment of Clarke (1883) (Möller et al.,2011). Previously, a chromosome number of
2n＝34 was also reported for two Oreocharis
species from China (Lu et al., 2002; Zhou et al.,2003). Although it is premature to conclude
whether Opithandra and Oreocharis are independent genera or not and the generic treatment ofO. primuloides, the present cytological study
suggests that these two genera sharing the same
chromosome number are closely related, inagreement with the molecular phylogenetic result(Möller et al., 2011).
Rhynchotechum discolor (Maxim.) B. L. Burttvar. discolor (Fig. 1E)
One plant of R. discolor var. discolor fromIshigaki Island of the Ryukyus showed a chromosome number of 2n＝20 (Fig. 1F), agreeing
with the chromosome count reported by Ratter(1963; no locality information); and that from
Taiwan by Wang and Wang (2000).
Titanotrichum oldhamii (Hemsl.) Soler. (Fig. 1G)
One plant of T. oldhamii from Iriomote Islandof the Ryukyus showed a chromosome numberof 2n＝40 (Fig. 1H), agreeing with that reportedby Ratter (1963).
Acknowledgments
This study was funded by a Grant-in-Aid for
Scientiﬁc Research (B) (JSPS KAKENHI Grant
Number 25290085).
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