Bull. Natn. Sci. Mus., Tokyo, Ser. B, 32(1), pp. 19–27, March 22, 2006

Distribution and Biogeography of Podostemaceae in Asia
Masahiro Kato
Department of Botany, National Science Museum, Amakubo 4–1–1, Tsukuba, 305–0005 Japan
E-mail: sorang@kahaku.go.jp

Abstract Podostemaceae are a family of ecologically and morphologically unusual aquatic angiosperms. The distribution maps of Asian Podostemaceae are provided here using results ofrecent studies, and a biogeographical scenario is proposed based on molecular phylogenetic anddistributional data. In the scenario, Podostemaceae or at least Podostemoideae and Weddellinoideae originated in Gondwanaland. Tristichoideae diversified in tropical Asia, with one species
migrating westward to Africa and then to South America. Weddellinoideae remained in SouthAmerica. Podostemoideae diversified first in tropical America and reiterated westward migrations
and radiations in Africa with Madagascar and then in Asia. Africa is a passageway for the westward and eastward migrations of the two families.
Key words : aquatic plants, biogeography, distribution, Podostemaceae, Thailand.

Introduction
Podostemaceae are a family of ecologicallyand morphologically unusual aquatic angiosperms. They occur on rocks in rapids andwaterfalls in the tropics and subtropics of theworld (Fig. 1) and are distributed in east, southeast and south Asia, Papua New Guinea, north
Australia, Africa, Madagascar and adjacentislands, and Central and South Americas (Fig. 2).
Central and South Americas harbor about 18
genera and 155 species, while 17 genera and 75
species, and 13 genera and 40 species are distributed in Africa and Asia, respectively (Cook,
1996). The numbers of genera and species are increasing by recent studies and they may reach intotal about 300 species. Vegetative plants growsubmerged in swift-running water during therainy season and subsequently emerge and eventually dry during the dry season when the waterlevel drops. Generally flowers open and seeds areset shortly after emergence. Except for a few
rootless species, the leading organ of the Podostemaceae plant is the root. It creeps on andadhere to rock surfaces (in some species floating
except at the base), is variously flattened ranging
from subcylindrical to ribbon-shaped or crustose,and bears adventitious, both vegetative and reproductive, shoots on the lateral flanks or dorsalside and root hairs (rhizoids) on the ventral surface (Fig. 1) (Willis, 1902b; Troll, 1941;
Rutishauser, 1997). Thus, the unusual root is aremarkable adaptation to the unique environment, i.e. the border between hard rock surfaces
and fast-running water. Such unique roots were
derived from cylindrical, underground roots common in most angiosperms including Clusiaceae(Hypericaceae), which are suggested to be themost closely related eudicot rosid family(Savolainen et al., 2000; Soltis et al., 1999, 2000;
Gustafsson et al., 2002).
The flowers are showy or in more species
inconspicuous. The showy flowers with a large
number of colored stamens, instead of pale or
reduced tepals, are insect-pollinated, while theinconspicuous, small flowers comprising a few
reduced tepals, stamens and carpels are primarily
wind-pollinated. The seeds are small and avoidof endosperm, due to lack of double fertilization.
After imbibition, the seed coats become quickly
glutinous to stick on wet rock surfaces, an adaptive character for seed germination in swift-running water. With such seeds Podostemaceae havea long-distance dispersal potential by vectors of20

Masahiro Kato

Fig. 1. Podostemaceae in nature. A. Apinagia populations in Essequibo River, Guyana. B. Terniopsis malayana
in Tahan National Park, Malaysia. Roots with short shoots on the flanks creep long on and adhere to rock surface. C. Polypleurum wallichii var. wallichii in Khao Yai National Park, Thailand. Ribbon-like roots with fascicles of few leaves on the flanks creep on and adhere to rock surface. D. Crustose root of Hydrobryum
japonicum in Kyushu, Japan. Note linear leaves (red purple) on the dorsal surface of the root. Scalebars5 mm.

Distribution of Podostemaceae

wind, birds, water, or fishes. Nonetheless, most
species are restricted to narrow areas, due tohardly identified factors.
I and colleagues have performed floristic studies of Podostemaceae in Thailand and adjacentregions (Kato & Hambali, 2001; Kato & Fukuoka, 2002; Kato & Kita, 2003; Kato et al., 2003;
Kato, 2004, in press). They record 34 species inThailand, six in China, seven in Laos, three inVietnam, two in Cambodia, and three in Indonesia. There are a few species in north India and
Myanmar. Only Dalzellia and Polypleurum arecommon genera in Southeast Asia and South
Asia. Genera that occur in extra-Thailand are Indotristicha, Hydrobryopsis, Willisia, and Zeylanidium, all of which are endemic to south India(Mathew & Satheesh, 1997). In comparison,many more genera, i.e. Cladopus, Cussetia,
Diplobryum, Hanseniella, Hydrobryum, Paracladopus, Terniopsis, and Thawatchaia, do notoccur in south India and Sri Lanka (Kato, 2004,
in press). This paper provides the distribution
ranges of Podostemaceae in Southeast Asia withneighboring regions, and a biogeographic scenario of the family.
Biogeography of Podostemaceae
A molecular phylogeny indicates that the family Podostemaceae comprises three subfamilies,
Podostemoideae, Weddellinoideae, and Tristichoideae, and the former two form a clade sisterto the last (Kita & Kato, 2001). This study andsubsequent results (Kato & Kita, 2003; Kato,
2004; Kita & Kato, 2004a, b) also show thatclades of the subfamilies are characterized geographically (Fig. 2). Weddellinoideae are monotypic with the sole species Weddellina squamulosa occurring in South America. Tristichoideae
with ca. 10 species are divided to two clades,
Terniopsis and a clade of Tristicha and a subclade of Dalzellia and Indotristicha. All genera
but Tristicha are Asiatic, while Tristicha is widely distributed in Africa, Madagascar and Southand Central Americas. Podostemoideae, thelargest subfamily with ca. 260 species, are divid-

21

ed to two clades, an American clade and a cladeof species occurring in all Asia, Africa andAmerica. The latter clade further diverges into an
Afro-American clade and an Asian clade. Hence,
the American Podostemoideae are basal and paraphyletic, while the African and Asian aremonophyletic.
The phylogeny, along with the distribution patterns and species richness, may suggest a scenario for the historical biogeography of Podostemaceae (Fig. 2): the family originated froma common ancestor with Hypericaceae in an unknown region in Late Cretaceous (72.4–76.4 million years ago; Davis et al., 2005). In this period,
Africa and South America, and India and Madagascar had begun to separate by the then lesswidened Atlantic Ocean, and the northeastwardly
drifting India was still far from the Asian continent, isolated by the Tethyan Seaway (Lomolino
et al., 2005). The low dispersability of narrowly
restricted species (but Tristicha trifaria) and the
distribution pattern of the family may suggestthat the possible place of origin is Gondwanalandor at least part of it. The early Podostemaceae
diverged into the Asian Tristichoideae and theAmerican clade consisting of Podostemoideae
and Weddellinoideae. After diversification of
Tristichoideae in tropical Asia and northward
expansion to China, a westward emigrant, i.e.
Tristicha trifaria, reached Africa and Madagascar with nearby islands (the Reunions and Seychelles) and later South America. Thus, Tristichoideae diversified in Asia and expanded into
north Australia, while a single species migrating
westward and ultimately to South and Central
Americas. The South American Weddellinoideae
did not diversified, compared to Tristichoideae
and Podostemoideae.
Podostemoideae show a primary diversification in South/Central America, and part of thesubfamily migrated to Africa and then to Asia
(Fig. 2). The migration took place in the opposite
direction to that of Tristichoideae, in the period
when the African continental island was separated from South America and also from Asia by
the Tethyan Seaway, and India approached and22Masahiro Kato

Fig. 2. Distribution map of Podostemaceae with phylogenetic tree adapted from Kita & Kato (2001, 2004a, b),
Kato et al. (2003), and Kato (2004). Solid and broken lines of tree indicate relationships of Podostemoideae
and Weddellinoideae, and Tristichoideae, respectively. Solid and broken arrows indicate intercontinental
migrations of Podostemoideae and Tristichoideae, respectively, followed by diversification in each continent.

ultimately collided with the Asian continent (Lomolino et al., 2005). The origin and migration
was followed by radiations of the subfamily ineach continent. It is noted that American
Podostemaceae are a mixture of the originallyneotropical Podostemoideae and the immigrating
Tristichoideae (Tristicha trifaria), along with theendemic Weddellinoideae, while Asian Podostemaceae are a mixture of the primarily Asian
Tristichoideae and the secondarily diversified Podostemoideae. Africa is not the place of origin,but a passageway for both the eastward migrationof Podostemoideae and the westward migrationof Tristichoideae.
The above is a parsimonious scenario for thehistorical biogeography of Podostemaceae. However, another but non-alternative possibility is not
excluded that the present distribution ranges areplaces of secondary diversification or include
them. For example, Asian Tristichoideae may beof Gondwana origin: the secondary diversification took place in Southeast Asia, subsequent to
the primary diversification in India, a part of
Gondwanaland, which had begun to split when
the Podostemaceae began to evolve. If this is correct, Podostemaceae might have originated inpart of Gondwanaland and expanded in different
ways via South America (for PodostemoideaeWeddellinoideae) and India (for Tristichoideae).
Both scenarios differ from Cusset & Cusset’s(1988) and Les et al.’s (1998) hypotheses, although they are similar in the Gondwana origin.
Cusset & Cusset (1988) and Les et al. (1998)
considered that Tristichoideae are a basal cladeof Podostemaceae that represents a Gondwana
floristic element with Tristicha trifaria distributed in Australia, tropical America, Africa, andMadagascar. However, this species is a crowntaxon in Tristichoideae and is likely to have very
recently migrated from Africa to America (KitaDistribution of Podostemaceae

23

Fig. 3. Distribution map of Terniopsis and Cussetia (Tristichoideae). Circles and dot indicate Terniopsis, andstars, Cussetia. Terniopsis sessilis occurs in China; T. malayana, T. ubonensis, T. brevis, and T. ramosa, inThailand; T. malayana, in peninsular Malaysia; and T. australis, in Australia. Cussetia diversifolia occurs in
Thailand and Laos; and C. carinata, in Laos and Cambodia.

& Kato, 2004a), and Australian populations arereferred to Terniopsis australis (Kato et al.,
2003; Kato, in press). Cusset & Cusset (1988)
furthermore suggested a northeastward and eastward migration of Tristichoideae, which is incorrespondence with our second scenario, although the phylogenetic relationship that underlies their hypothesis may not be correct. Les etal. (1998) hypothesized that tropical radiations
happened first in South/Central America and second in Asia, based on an rbcL-deduced phylogeny. Although they did not examine African
species, the hypothesized historical biogeographyof Podostemoideae agrees with ours based on a
matK-deduced phylogeny. From a correspondence of trees deduced from the different genes,
it is summarized that reiterated radiations following migrations forced diversification of Podostemaceae in the Cenozoic (Fig. 2).

Distribution Ranges of Genera in Thailand
and Adjacent Regions
The taxonomy of species of subfamily Tristichoideae has recently been revised by Kato (inpress). Among the five genera assigned to thesubfamily, Cussetia is endemic to Southeast Asia
(eastern Thailand, Laos and Vietnam) (Fig. 3).
Terniopsis consists of six species, of which four
species occur in peninsular, central and eastern
Thailand (one species extends south to peninsular Malaysia), T. sessilis in central-eastern China,
and T. australis in the northern part of Northern
Territory and Western Australia, Australia (Katoet al., 2003) (Fig. 3). These two extra-Southeast
Asian species of Terniopsis are not basal in aphylogenetic tree (Kita & Kato, 2001; Kato etal., 2003, Y. Kita, unpubl. results). Dalzellia zeylanica and D. gracilis occur in south Asia, i.e.
southeast India and Sri Lanka (Willis, 1902a, b;
Mathew & Satheesh, 1997; Mathew et al., 2001),
while four species occur in Thailand (Fig. 4). The
remaining genus Indotristicha with I. ramosissi-

24

Masahiro Kato

Fig. 4. Distribution map of Dalzellia (Tristichoideae). Dalzellia ubonensis, D. ranongensis, D. kailarsenii, and D.
angustissima occur in Thailand; and D. zeylanica and D. gracilis, in India and Sri Lanka, and India, respectively. The distribution range of D. zeylanica in India almost overlaps with that of Indotristicha.

Fig. 5. Distribution map of Polypleurum (Podostemoideae). Polypleurum wallichii var. wallichii and var.
parvum, P. schmidtianum, P. longistylosum, P. longifolium, P. wongprasertii, P. phuwuaense, P. rubroradicans,
P. erectum, and P. longicaule occur in Thailand; P. wallichii var. wallichii occurs also in India and Laos; P. filifolium, P. munnarense, P. dichotomum, P. elongatum, P. stylosum, P. prostratum, and P. disciforme, in south
Asia (India and/or Sri Lanka).

Distribution of Podostemaceae

ma and I. tirunelveliana occurs in southeastern
India. Deduced phylogenetic relationships indicate that the first divergence occurred between
Terniopsis and the rest of the subfamily. The latter clade diverged into Tristicha and a clade of
Dalzellia and Indotristicha (Kita & Kato, 2001,
2004a). Tristicha is exceptional in its supercontinental distribution in Africa and America, while
all other genera are distributed in Asia and Australia. As aforementioned, the subfamily Tristichoideae diversified first in tropical Asia andlater the monotypic Afro-American Tristicha migrated to tropical Africa and further to tropical
America recently by long-distance dispersal(Kita & Kato, 2001, 2004a).
Concerning the subfamily Podostemoideae,
more species (9) of Polypleurum occur in Thailand than in South Asia (ca. 7 spp.; Mathew etal., 2003) (Fig. 5). Most of the nine species areendemic to Thailand, but Polypleurum wallichii

25

is distributed in north India, east Myanmar andLaos in addition to Thailand (Kato, in press). As
the north Indian-Southeast Asian P. wallichii isclosely related to the south Asian P. stylosum(Kita & Kato, 2001), the phylogeny of Polypleurum does not exhibit an obvious geographic pattern. Two species of Cladopus occur in Thailand,
while several other species are distributed in thesurrounding southeastern and eastern Asia (theIndian C. hookerianus may not be congeneric)(Fig. 6). The genus comprises an eastern Asianclade distributed in China and Japan, and aSoutheast Asian clade distributed in Thailand,Laos, Vietnam, Indonesia, Papua New Guinea,
and northeastern Australia. Paracladopus withthe sole species P. chiangmaiensis, endemic to
Thailand, is basal in the Cladopus clade (Kato, inpress). Cladopus may be likely to have originatedin Thailand or Southeast Asia and expanded toJapan and Australia. In the monophyletic group

Fig. 6. Distribution map of Paracladopus and Cladopus (Podostemoideae). Paracladopus chiangmaiensis (star),
Cladopus taiensis, and C. fallax occur in Thailand; C. fallax and “C. nymanii” in Vietnam; C. pierrei in Laos;
C. nymanii, and C. javanicus, in Indonesia; C. queenslandicus, in Papua New Guinea and Australia; C.
japonicus, C. fukienensis, and C. austrosinensis, in China; and C. japonicus, C. doianus, C. austro-osumiensis, in Japan.

26

Masahiro Kato

Fig. 7. Distribution map of Hydrobryum (circles, dot), Hanseniella (squares) and Thawatchaia (star) (Podostemoideae). Hanseniella heterophylla, Ha. smitinandii, Thawatchaia trilobata, Hydrobryum bifoliatum, H.
kaengsophense, H. tardhuangense, H. griffithii, H. loeicum, H. somranii, H. chiangmaiense, H. japonicum,
H. khaoyaiense, H. micrantherum var. micrantherum and var. crassum occur in Thailand; H. griffithii, in India
and Vietnam; H. griffithii and H. japonicum, in China; H. japonicum, H. floribundum, H. koribanum, and H.
puncticulatum, in Japan. Diplobryum minutale of southern Vietnam and D. vientianense of northern Laos (asterisks), like the three genera, have crustose roots, but their phylogenetic relationships are uncertain.

comprising three crustaceous-rooted genera,
most (8) of ca. 11 species of Hydrobryum occurin Thailand, and Hanseniella and Thawatchaia
are endemic to Thailand (Kato, 2004) (Fig. 7).
The phylogeny that the last two genera are basal
in the clade of the crustaceous-rooted genera, andThai species of Hydrobryum are also basal in thegenus (Kita & Kato, 2004b), suggests that thesecrustaceous-rooted genera may have originated in
Thailand or Southeast Asia. The present distribution of Hydrobryum extending to Japan and theHimalaya may be a result of past northward expansions. Surprisingly, Hydrobryum japonicum is
distributed disjunctively in Japan, southern Yunnan (China), and northern Thailand, likely due tothe subsequent southward dispersal (Kita &Kato, 2004b).
In conclusion, the present distribution of Podostemaceae may be results of both eastward andwestward intercontinental migrations of two subfamilies in different geological times during the
Cenozoic. Thailand with the close adjacentregions, like South Asia, is a core region for thediversification of all genera of Podostemaceae in
Asia, while other regions, e.g. Myanmar, China,
Japan, Malaysia, Indonesia, Papua New Guinea,
and Australia, are peripheral for their expansions.
Acknowledgments
I thank T. Santisuk, T. Wongprasert, R.
Imaichi, H. Akiyama, Y. Kita, S. Koi, S.-J. Lin,
J.-K. Liu, B.-H. Cheng, A. K. Pradeep, P. Mathew, K. Suzuki, B. D. Sumithraachchi, and S.-K.
Wu for their help during collecting trips; F. Montana, S. Suddee, P. Phonsena, Y.-F. Deng, T.-L.
Wu, and T. Yamada for kindly providing materials used in recent work. This study was partly
supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotionof Science.
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