DSpace at VNU: The oldest flora of the South China Block, and the stratigraphic bearings of the plant remains from the Ngoc Vung Series, northern Vietnam

Journal of Asian Earth Sciences 43 (2012) 51–63

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Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes

The oldest flora of the South China Block, and the stratigraphic bearings
of the plant remains from the Ngoc Vung Series, northern Vietnam
Paul Gonez a,⇑, Hung Nguyên Huu b, Phuong Ta Hoa c, Gaël Clément d, Philippe Janvier d
a

Palaeobiogeology, Palaeobotany, Palaeopalynology, Department of Geology (B18), University of Liège, allée du 6 aout, Sart Tilman, 4000 Liège 1, Belgium
Vietnam National Museum of Nature, 18 Hoang Quoc Viet Str., Hanoi, Viet Nam
c
Vietnam National University, Department of Geology, 334 Nguyên Trai Street, Thanh Xuan, Hanoi, Viet Nam
d
Muséum National d’Histoire Naturelle, UMR-CNRS 7207 CR2P, Bâtiment de Paléontologie, CP 38, 47 rue Cuvier 75231 Paris cedex 05, France
b

a r t i c l e

i n f o

Article history:
Received 14 October 2010
Received in revised form 12 July 2011
Accepted 25 August 2011
Available online 10 September 2011
Keywords:
Early land plants

Zosterophylls
Late Silurian
Basal euphyllophyte
Early Devonian
Phytogeography
Vietnam

a b s t r a c t
Several outcrops of the Late Silurian and Devonian of the Ngoc Vung Series, northern Vietnam, yielded
plant remains. The Late Silurian localities delivered the earliest known flora of the South China block.
Although the fossils are fragmentary, they complement our knowledge about the global composition
of the flora. The major components of the flora are plants with dichotomous habit and terminal bivalvate
sporangia, which are close relatives to zosterophylls, and zosterophylls. Plants with possible euphyllophyte affinities and bryophytes are occasionally present. This floral composition is similar to that of
the rich, younger South China block assemblages from the Posongchong and Xujiachong Formations of
China, considered Pragian in age. The South China block flora is therefore likely to have been dominated
by zosterophylls and pre-zosterophylls at least from the Late Silurian to the Pragian (i.e. a 20 million
years long period). It also strengthens the hypothesis that more derived plants were present on eastern
Gondwana earlier that elsewhere, in the first steps of tracheophyte evolution. The Devonian localities of
the Ngoc Vung Series delivered a thick fibrous stem fragment and a basal euphyllophyte. These latter
plant remains provide some stratigraphic data. The large stem fragment is consistent with an Eifelian
age for the Duong Dong Formation (part of the Ngoc Vung Series), as suggested by the brachiopod fauna.
The accompanying basal euphyllophyte displays a combination of characters (axes 3–4 mm wide and lateral branchings) that is also consistent with an Eifelian age, but possibly more characteristic of the
Emsian flora. It is therefore suggested that the stratigraphic range of the Duong Dong Formation might
be extended down to the Emsian.
Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction
Early land plants of Vietnam have hitherto barely been studied:
only three accounts have been published. In central Vietnam,
Dovjikov (1965) reported the occurrence of two zosterophylls

(Zosterophyllum sp. and Gosslingia sp.) in the Tay Trang Formation,
Lower Devonian. Concerning northern Vietnam, Tran et al. (1964)
mentioned the presence of Eogaspesia sp. in the Lower Devonian
Si Ka Formation, but specimens are not figured. Janvier et al.
(1987) mentioned the presence of two specimens of Cooksonia
sp. in Dô Son peninsula, in an outcrop of the Ngoc Vung Series
(according to the latest stratigraphic zonation by Nguyên et al.
(2007)). This Dô Son plant locality is currently regarded as Late
Silurian (probably Pridolian) in age (Janvier et al., 1987, 2003;
Braddy et al., 2003) and belongs to the South China block. The fossil

⇑ Corresponding author. Tel.: +32 43665260.
E-mail address: (P. Gonez).
1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jseaes.2011.08.007

plants from Dô Son thus represent the oldest known flora of the
South China block.
The Ngoc Vung Series do not however only include Upper Silurian
sediments. Its stratigraphic extension is likely to encompass Upper
Silurian to Eifelian strata (Hung et al., 2007). The stratigraphic
scheme of the series is still debated and commented in several recent publications (Tong et al., 2006, in press; Nguyên et al., 2007).
More precise stratigraphic data are still badly needed for these plant
localities of northeastern Vietnam. Here we present a detail study of
new material sampled in several fossil plant localities (including Dô
Son) of the Ngoc Vung Series, northeastern Vietnam, along with a reinvestigation of the material figured by Janvier et al. (1987). The
work on the Dô Son locality aims to assess the floral composition
of the oldest flora of the South China block. We discuss its affinities
with the younger South China block floral assemblages, such as
those of the Early Devonian Posongchong and Xujiachong Formations, and with the coeval Khazakhstanian assemblage from the

Wutubulake Formation of China. The second goal of this work is to
consider the bearings of the other palaeobotanical samples of the


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Ngoc Vung Series on the stratigraphy of the Middle Palaeozoic of the
Quang Ninh area.

2. Geology
2.1. Main features of the Ngoc Vung Series
The Ngoc Vung Series mainly yield exposures in two areas: the
Haiphong area and Bai Tu Long Bay (Fig. 1). In Bai Tu Long Bay,
exposures are restricted to the easternmost islands, including Tra

Ban, Quan Lan and Ngoc Vung (Fig. 1A). In the Haiphong area,
the main exposure is the hill of Ngoc Xuyen townlet, on the Dô
Son peninsula (Fig. 1B).
The Ngoc Vung Series are comprised of two formations (from
base to top). The Van Canh Formation is about 400 m thick. Its lower boundary has been observed during recent fieldwork (December
2010) in Kien an. The Van Canh Formation is comformably underlain by the Kien an Formation, which is Ludlow-Pridoli in age (Tong
et al., 2006). The lithology of the Van Canh Formation consists of
coarse-grained quartzitic sandstones, interbedded with grey clay
and siltstone lenses. Fossils are found in clay and siltstone lenses,

Fig. 1. Location of the investigated localities from the Ngoc Vung Series: (A) in Bai Tu Long Bay; (B) on the Dô Son peninsula, Haiphong area (redrawn from Chu et al., 2001;
Dang et al., 2001). Grey areas: outcrops of the Ngoc Vung Series. Localities 1–3 are part of the Van Canh Formation; localities 4 and 5 are part of the Duong Dong Formation.

P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

mostly at Dô Son. They are mainly eurypterids (Janvier et al., 1989;
Braddy et al., 2003), but placoderms, lingulids and early land plants
fragments are also common (Janvier et al., 1987). Sedimentology
suggests that the Van Canh Formation represents alluvial channels
in a deltaic system, with a slight marine influence in Dô Son, as
suggested by the presence of eurypterids, acritarchs and scolecodonts (Braddy et al., 2003).
The Van Canh Formation is comformably overlain by the Duong
Dong Formation. The latter is 130 m thick in the type locality but
lateral variations of thickness exist (Fig. 2). Although its lithology
is roughly similar to that of the Van Canh formation, its palaeontological facies is different. The siltstone lenses mostly contain various brachiopods, which suggest a plainly marine environment
(Nguyên et al., 2007). The Duong Dong Formation is uncomformably overlain by the Middle-Upper Devonian Dô Son Formation.
On the Dô Son peninsula, the Duong Dong Formation does not appear. There is most probably a lack of sedimentation between the
Van Canh Formation and the Dô Son Formation, which are only
separated by an erosion surface at Xom Chê quarry (Janvier et al.,
2003).
2.2. Age of the Ngoc Vung Series
Palynological samples were collected in each locality of the
Ngoc Vung Series we prospected, but did not yield any spore (contra Braddy et al., 2003).
Fossils are relatively rare in the Van Canh Formation. They are
mostly recovered from the Dô Son peninsula. A Late Silurian age is
suggested for the Van Canh Formation (at any rate on the Dô Son
peninsula) on the basis of several macrofossils, namely the eurypterid Rhinocarcinosoma (Braddy et al., 2003), the inarticulate brachiopod Laima (Janvier et al., 1987) and several placoderm fish
remains, one of which can be referred to the nomen nudum ‘Wangolepis’ hitherto recorded exclusively from the Silurian of China
(Nguyên et al., 2007). However scarce are these macrofossils, fishes
are clearly different from the now classical Lochkovian-Pragian taxa
of northern Vietnam and South China, but closer to those found in

53

association with undoubtedly Ludlow-Pridoli marine invertebrates
at My Duc, Quang Binh Province (Janvier et al., 2003). Moreover,
Braddy et al. (2003) reports that palynological samples from locality
2 (Fig. 1B) studied by Marshall yielded spores that indicate a Late
Silurian age for this locality. Yet we failed to find any evidence for
palynomorphs from the same locality.
The overlying Duong Dong formation is regarded as Eifelian in
age, at least in its uppermost beds, according to the brachiopods
fauna. However, it is strongly suspected to be diachronic, as some
lower beds yield fossils that are characteristic of the Pragian Euryspirifer tonkinensis assemblage (Janvier et al., 2003; Tong et al.,
2006; Nguyên et al., 2007). The Duong Dong Formation is most
likely to encompass Pragian to Eifelian sediments. Therefore, the
Ngoc Vung series are comprised of deltaic deposits that may range
in age from the Upper Silurian to the Lower Middle Devonian.
2.3. Palaeogeographic location of the Ngoc Vung Series
The Ngoc Vung Series are part of the South China block. It is
considered as a perigondwanan terrane. It was located on the
equator throughout the Devonian times, probably very close to
the Gondwana, on the eastern side of the continent (Scotese, 2010).
3. Materials and methods
We have investigated five outcrops of the Ngoc Vung Series.
Three of them are located in the Bai Tu Long Bay area (Fig. 1A).
(1) The road cut of the path that runs along the western coast of
Tra Ban Island is part of the Van Canh Fm. It exhibits thin bedded
silts and clays, rather crumbly and light brown coloured, in which
occur plant fragments. (4) The natural exposure on the eastern
beach of Quan Lan Island north of Minh Chau belongs to the Duong
Dong Fm. It consists vertical strata of grey bluish silts scarcely popping out from the sand of the beach. They only released one fossil

of vegetal origin. (5) The quarry along the road heading from the
Ngoc Vung Island harbour is also part of the Duong Dong Fm. It
displays a vertical outcrop in which grey bluish silt lenses are

Fig. 2. Stratigraphic sketch of the investigated localities and position of the studied samples. Tk: thickness. Dotted layers: sandstones; dashed layers: siltstones and clays;
layers with circles: conglomerates; rippled lines: unconformity.


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P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

interbedded in thick horizontal sandstones layers. The silt lenses
yield large plant fragments, but they are difficult to access, so only
small rock fragments have been sampled. The other two exposures
are on the Dô Son peninsula (Fig. 1B): (2) an old quarry along the
northern slope of the hill of Ngoc Xuyen and (3) the Xom Che quarry. Both of those outcrops are part of the Van Canh formation and
consist of grey bluish clay silt lenses interbedded in coase grained
sandstone. The silt lenses deliver some small plant fragments and
abundant eurypterid remains. Localities 1, 2 and 3 are part of the
Van Canh Formation; localities 4 and 5 are part of the Duong Dong
Formation (Fig. 2). The material is housed in the Geology Museum
(Bao Tang Dia Chat), Hanoi, Vietnam. We also re-observed the
material figured by Janvier et al. (1987), which was sampled in
the locality 3. The material belongs to Geology Museum, Hanoi,
Vietnam, some specimens being still provisionally deposited in
the Museum National d’Histoire Naturelle, Paris.
All the fossil plants we collected are adpressions sensu Shute
and Cleal (1987), e.g. ‘‘plant fossil specimen showing a mixture
of compression and impression states’’. They were prepared and

studied according to standard palaeobotany techniques. All specimens were freed from the sediment that partially embeds them
by means of the technique called ‘‘dégagement’’: sediment covering the fossil surface is removed by sharpened needles under a dissection microscope (Fairon-Demaret et al., 1999). The specimens
were measured from digital photographs taken with a Zeiss Stemi
2000C stereomicroscope equipped with a CCD camera and the software AxioVision digital image processing. We attempted scanning
electron microscopy observations on two three-dimensionally preserved specimens, but no cellular detail was available.
4. Results
4.1. Localities from the Van Canh Formation
4.1.1. Locality 1: vegetative features
Locality 1 only yielded tiny, unbranched axes portions, the
width of which ranges from 0.25 to 0.5 mm.
4.1.2. Localities 2 and 3
4.1.2.1. Vegetative features. The localities, close to each other, are
here described and discussed together.
Locality 2 delivered the best preserved fossils. Slender axis fragments were recovered. They are about 1–1.5 mm wide and exhibit
a distinct central strand, 0.1–0.12 mm wide, the cells of which are
not preserved (Fig. 3A). A bulbous structure sticking out from an
unbranched axis was also released by ‘‘dégagement’’ technique
(Fig. 3B). The vascular trace displayed by the axis does not penetrate the bulged structure. This can either be a preservation artefact or the indication of an unvascularized structure. The bulbous
structure looks like a slightly vertically stretched bladder. It is
0.65 mm wide and 0.8 mm high.
Sixty-five samples were collected at Xom Che quarry, locality 3.
Vegetative remains are very abundant. Most of the vegetative fragments are unbranched axes, sometimes of a great length: the longest is 14 cm. They occasionally exhibit a coalified central strand,
0.1–0.15 mm wide. Sometimes, the central strand preserves the
outline of elongated cells (Fig. 3C and D). The cells are about
400 lm long and 20 lm wide.
All axes are smooth and of constant diameter. Many instances of
branching axes are recovered, and commonly display K-type
branchings (Fig. 3E). Those axes are 0.25–0.7 mm wide. Some trichotomies (Fig. 3F) are also encountered, but they most probably
result from the folding of a K-type branching. They display the
same width range. The presence of lateral branchings that dichotomize (Fig. 3G) is noteworthy. The main axis of this system is

0.55 mm wide. The lateral branch is 0.15 mm wide and its two
daughter-axes are 0.1 mm wide. Isotomous branchings are rare.
Two minute, delicate fossils display peculiar features. Specimen
ST390-7 exposes a slender axis, 0.2 mm wide and 4 mm long. This
axis bears a lateral pointed structure on each of its sides. The
pointed structures are 1.5–2.2 mm long and are roughly bananashaped (Fig. 3H). There are two possible interpretations for those
unbranched lateral structures. (1) Those banana-shaped emergences could be sporangia. Rebskia musaeformis Schweiter 2000,
from the Emsian of Germany, also displays banana-shaped sporangia. However, those are much bigger (5–7 mm), terminal, and exhibit a rounded structure at their apex (Schweitzer, 2000). Thus our
specimens are clearly different from Rebskia. Moreover, we are
reluctant to favour the sporangia hypothesis, because the only
known plants with lateral sporangia in the Late Silurian are lycophytes or lycophytes-like plants, i.e. with reniform and dehiscent
sporangia. (2) The second hypothesis is that those structures are
microphylls. The size and shape are consistent with this interpretation. This hypothesis is more parsimonious, because microphylls
are the characteristic vegetative lateral organs of lycophytes; and
early lycophytes had already evolved by the Late Silurian (Kotyk
et al., 2002). The oldest occurrence of microphylls is gedinnian
(i.e. the equivalent of the Lochkovian) (Schweitzer, 1982).
Specimen ST390-8 also consists of a slender axis, 0.2 mm wide
and 4.9 mm long. It shows a 0.8 mm long, bifurcating lateral structure. The basal part is 0.25 mm long; the two furcas are longer.
They have different lengths: 0.25 and 0.55 mm. They both demonstrate a pointed end (Fig. 3I). Once again two interpretations are
possible for this structure: either it can be interpreted as a sporangium or as a lycophyte lateral vegetative organ. The sporangium
hypothesis is not favoured, according to the same arguments.
Though bifurcating sporangia are reported in the Late Silurian
(Fanning et al., 1991), their shape is rather different and they are
borne terminally. We consider that the vegetative organ hypothesis is more parsimonious. This structure will therefore be tentatively interpreted as a bifurcating microphyll, yet multifurcate
microphylls only appear by the Emsian in the fossil record (Gensel
and Kasper, 2005).

4.1.2.2. Sporangia. Eleven complete sporangia were recovered in

locality 3. They demonstrate a significant variation in size and
shape (Fig. 4), thus testifying of the diversity of the original flora.
The biggest sporangium (Fig. 5A) is 3.9 mm high and 2.35 mm
wide. It is borne by a 7.9 mm long portion of unbranched slender
axis, 0.5 mm wide. The lower portion of the sporangium consists
in an abrupt widening of the subtending axis, at an angle of 60°.
The upper part of the sporangium has a more irregular and curved
outline. This structure resembles the body illustrated by Edwards
et al. (2001, Fig. 36). The authors compare this structure to Tarrantia Fanning et al. 1992. We disagree with this comparison. Tarrantia
exhibits a more regular oval or ovoid outline, and the dimensions
of its sporangium are smaller (around 1 mm high). We would
rather attribute our specimen to the genus Sporogonites Halle,
1916. Most of the features match Halle’s diagnosis (1916): ‘‘spore
producing body consisting of a simple stalk and a terminal capsule.
Stalk 0.5 mm in diameter and up to at least 50 mm long, faintly
striated longitudinally. Capsule elongated or clavate, 6–9 mm long
and 2–4 mm in diameter in the thicker upper part, with a rounded
apex and a tapering base [. . .]’’.The only absent characters are the
striation of the stalk and the spores. The smaller dimensions of
our specimen are characteristic of S. yunnanense Li 1966. Yet our
specimen does not show any pointed apex, and the elongated epidermal cells of the wall of the capsule mentioned in Li’s diagnosis
are not perceptible. Therefore, we provisionally refer to the specimen as cf. Sporogonites yunnanense.


P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

55

Fig. 3. Remarkable vegetative features of the plant remains from the Dô Son peninsula, Van Canh Formation: (A) specimen ST390-1, axis exhibiting a central strand; (B)
specimen ST390-2, bulbous structure emerging from an unbranched axis; (C) specimen ST390-3, axis preserved as the outlines of the cells are perceptible, general view; (D)

specimen ST390-3, detailed view; (E) specimen ST390-4, K-type branching; (F) specimen ST390-5, the central daughter internodes is dichotomous; (G) specimen ST390-6, the
main axis bears a lateral branch that is dichotomous, only the coalified central strand of the whole branching system is preserved; (H) specimen ST390-7, axis portion that
bears two structures tentatively interpreted as microphylls; (I) specimen ST390-8, axis portion that bears a lateral original structure tentatively interpreted as a bifurcating
microphyll.


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P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

and Gerrienne, 2010b). The rounded bodies are more likely to be
oval to reniform sporangia similar to those described above, i.e.
probably bivalved and dehiscent. The lack of morphological detail
prevents from a more precise determination.
4.1.2.3. cf. Filiformorama Wang et al., 2006. The specimen (Fig. 5M
and N), found in locality 3, is 26 mm long. Axes are constant in
diameter and their curves hint that they were flexible in life. The
main axis is 0.3 mm wide. Our specimen displays one single anisotomous branching at the base of the main axis. The lateral axis is
5.6 mm long for 0.2 mm wide and unbranched (Fig. 5M). The terminal body is 0.45 mm high for 0.5 mm wide, poorly and incompletely preserved (Fig. 5N). It is interpreted as the base of a
terminal structure, most probably a sporangium. Those features
are reminiscent of Filiformorama Wang et al., 2006. However, Filiformorama sporangia are bigger and tongue-shaped or reniform
(Wang et al., 2006). Here poor preservation prevents from a secure
three-dimensional reconstruction of the terminal body. Therefore,
we refer this specimen to cf. Filiformorama sp. with great
reservation.
Fig. 4. Outlines of the sporangia population from Xom Che quarry, Van Canh
Formation. (A) ST390-11; (B) ST390-12; (C) ST390-13; (D) ST390-14; (E) ST390-15;
F: ST390-17; G: ST390-16; (H) ST390-6; (I) ST390-10; (J) ST390-9.

Another terminal body is clearly vertically stretched. It is

0.42 mm wide and 0.67 mm high, and is tentatively interpreted
as an elongated sporangium of unknown affinity (Fig. 5B).
The remaining nine sporangia are all rounded to reniform in
shape, but exhibit different characteristics. Their width ranges
from 1.17 to 3 mm, and their height from 1.78 to 2.57 mm. The
limit between the sporangia and the subtending axis could not
be defined clearly in these specimens, due to preservation.
Two specimens terminate isotomous axes (Fig. 5C–E). The terminal branches of the largest specimen (Fig. 5C and D) are
5.18 mm and 4.27 mm long. The sporangia are rounded, respectively 2.75 mm high–3.0 mm wide, and 2.57 mm high–3.23 mm
wide. They are the largest ones found in this locality. Specimen
ST390-12 (Fig. 5E) is more slender: the only complete terminal
branch is 3.15 mm and the single preserved sporangium is
1.7 mm high. Sporangium width cannot be measured with certainty due to deformation. Nevertheless, this sporangium shows
a conspicuous rim parallel to the sporangial outline. This feature
is interpreted as a sub-distal dehiscence line. It is one of the smallest sporangia of the flora.
The other specimens are borne by unbranched axes. Sporangial
dimensions do show significant variation: their width ranges from
1.17 mm to 2.22 mm, and their height from 1.78 mm to 2.21 mm
(see also Fig. 4). Among the latter, three exhibit a longer subtending axis (Fig. 5F–H): respectively 5.18 mm, 4.0 mm and 2.9 mm. A
sub-distal dehiscence line is perceptible on specimens ST390-14
and ST390-13 (Fig. 5F and G). The latter (specimen ST390-15,
Fig. 5H) shows that its two valves are separated and are clearly unequal in size.
The last three specimens are borne by short portions of subtending axis, whose length ranges from 1.75 to 2.17 mm. These
three sporangia consist of oval to reniform bodies (Fig. 5I–K).
One of them exhibits a clear sub-distal dehiscence line (Fig. 5I).
Sporangial wall of another is ornate with a reticulum (Fig. 5K–L).
We also re-observed the material figured by Janvier et al. (1987)
who mentioned the presence of Cooksonia Lang 1937 sporangia in
the flora. These sporangia are weak impressions of rounded bodies
with a slightly blurred outline, due to poor preservation. They do

not match with the updated definition of Cooksonia, which states
that the sporangium is characteristically trumpet-shaped (Gonez

4.2. Localities from the Duong Dong Formation
4.2.1. Locality 4
Locality 4 yielded larger axes, 1–6 mm wide, one of which could
possibly be trifurcate, but bad preservation prevents from assessing it with certainty. A poorly preserved specimen is of much larger
size. The fragment is 16 mm wide for 14 mm high. The texture of
the preserved organic matter is porous and the outline of the fibres
is clearly perceptible (Fig. 6A). This fossil could be a wood fragment. However, the preservation prevents from assessing that with
certainty: neither aligned tracheids, nor vascular rays can be demonstrated. We will therefore consider that this fragment is part of a
large plant, stems at least 1.5 cm large, whose stem anatomy is
fibrous.
4.2.2. Locality 5
Locality 5 yielded plant fragments of different sizes. The larger
remains are 3.3–4 mm wide and display anisotomous branchings,
the lateral emissions are 1.7–2 mm wide. They are inserted at
120° (Fig. 6B). The width of the main axis is large and constant.
The fragment is thus interpreted as a proximal or median part of
the stem. In one fragmentary specimen, the main axis (3.2 mm
wide), tapers to 2 mm after two successive lateral emissions that
are 1.7 mm wide. Here the width of the main axis is less important
and tapers distally. The fossil is thus interpreted as a distal part of a
main axis, close to the apex. The 1.7 mm wide lateral emissions of
this specimen are branched isotomously (Fig. 6C). The smaller remains are dichotomous systems that sometimes terminate in
pointed recurvations (Fig. 6D). The latter can also be found as dispersed organs in the sediment (Fig. 6C).
5. Discussion
5.1. Floral composition of the localities
5.1.1. Locality 1
The fragmentary preservation of the vegetal remains prevents

from providing a precise floral composition. However, the fact that
all, very abundant, axis fragments are all very short and narrow
suggests that the flora was likely to be comprised of early embryophytes, probably with a rhyniophytoid architecture, i.e. with
dichotomous axes and terminal sporangia. ‘‘Rhyniophytes’’ have
been demonstrated to be polyphyletic (Kenrick and Crane, 1997),


P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

57

Fig. 5. Fertile remains from Xom Che quarry, Van Canh Formation: (A) specimen ST390-9, cf. Sporogonites yunnanense; (B) specimen ST390-10, terminal structure interpreted
as a sporangium of previously unknown morphology; (C) specimen ST390-11, rounded sporangia borne on isotomous axes; (D) specimen ST390-11, counter-part; (E)
specimen ST390-12, reniform dehiscent sporangium borne by isotomous axes; (F) specimen ST390-13, rounded dehiscent sporangium; (G) specimen ST390-14, reniform
dehiscent sporangium; (H) specimen ST390-15, sporangium with unequal valves, the larger upper valve is broken, and thus reveals part of the lower smaller one; I, specimen
ST390-16, rounded dehiscent sporangium; (J) specimen ST390-6, oval sporangium; (K) specimen ST390-17, sporangium with a reticulate wall; (L) specimen ST390-17, detail
of the reticulum; (M) specimen ST390-4, cf. Filiformorama sp., general view, the arrow points toward the anisotomous branching; N, specimen ST390-17, cf. Filiformorama sp,
detail of the terminal body interpreted as the base of a sporangium.

the preferred term ‘‘rhyniophytoid’’ (Pratt et al., 1978) only refers
to a morphology, and does not convey any taxonomic bearing.
5.1.2. Localities 2 and 3
Our fossils demonstrate a rather remarkable diversity in the
flora of the Van Canh Formation on the Dô Son peninsula.
Bulbous structures similar to those we found in Dô Son have
hitherto only been demonstrated in two taxa. (1) In the tracheophyte Bitelaria dubjanskii Istchenko & Istchenko 1979, similar bulbous structure are present, but they occur as clusters (Johnson and
Gensel, 1992). (2) Stockmansella remyi Schultka and Hass, 1997 is a
Rhyniopsida sensu Kenrick and Crane, 1997 (Paratracheophyta
Gerrienne et al., 2006). It consists in dichotomous creeping axes
with lateral hazelnut-shaped sporangia, and rhizoid-bearing

bulges (Schultka and Hass, 1997). The rhizoid-bearing bulges look

similar in shape to that we illustrate on figure 3B. However, they
are much smaller: 0.2–0.3 mm wide for 0.3–0.5 mm long (Schultka
and Hass, 1997). As those bulbous structures would be the only
and weakest clue for the presence of this taxon, we are reluctant
to postulate that the flora might have contained Rhyniopsida/
Paratracheophyta. In brief, this bulged structure cannot be referred
to any existing taxon.
Sporogonites is believed to be a plant at a bryophytic grade of
organization (Halle, 1916; Andrews, 1960; Kenrick and Crane,
1997).
The rounded to reniform sporangia terminating dichotomous
axes are relevant to plants with rhyniophytoid architecture. At
least two taxa were present in this locality. Firstly, a taxon represented by plants with large, rounded sporangia; secondly a taxon
with sporangia showing a sub-distal dehiscence line. Compression


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Fig. 6. Remarkable vegetative features of the plant remains of the Duong Dong Formation: (A) specimen ST390-18, large fibrous stem fragment from locality 4; (B) specimen
ST390-19 from locality 5, main axis showing lateral branches inserted at 120°; (C) specimen ST390-20 from locality 5, main axis that tapers after two successive lateral
emissions, inserted at 120°, the lateral emissions are dichotomous systems, the tapered axis branch near the edge of the fossiliferous block, arrow points to at an isolated
recurved tip; (D) specimen ST390-21 from locality 5, vegetative ramified system, the terminal branches are recurved tips, some of them are indicated by arrows.

fossils of plant with rhyniophytoid architecture and rounded to
reniform sporangia are represented by three genera: Uskiella Shute
& Edwards 1989, Renalia Gensel 1976, Hsüa Li 1982 (Gonez and

Gerrienne, 2010a). The specimen with large rounded sporangia
cannot be attributed to any of those taxa, because of the lack of
morphological details on its sporangia. Our second specimen
shares a feature in common with Aberlemnia Gonez & Gerrienne
2010: it possesses a sub-distal dehiscence line (Gonez and Gerrienne, 2010a). Yet, other sporangial characters defining the genus
are not displayed: the features of the sporangium/subtending axis
limit are not preserved. We will therefore refer to the specimen as
cf. Aberlemnia sp. Aberlemnia, and possibly other plants of rhyniophytoid architecture with reniform dehiscent sporangia, are most
probably a stem-group of early lycophytes, i.e. zosterophylls (Gonez and Gerrienne, 2010b). Other incertae sedis plants with different or unknown architecture (such as cf. Filiformorama or the
putative elongated sporangia) are present in this locality.
Other rounded to reniform sporangia are borne by unbranched
portions of axis. Three specimens each demonstrate a distinctive
feature (reticulate sporangial wall, subdistally dehiscent sporangium, unequal valves), which suggests that there were at least
three different taxa of parent plants. Two interpretations are possible for those sporangia borne by unbranched short portions of axis.
(1) The fossils are broken parts of terminal dichotomous axis. In
this case, the fossils represent other taxa of plant with rhyniophytoid architecture and reniform sporangia, i.e. stem-group of zosterophylls. (2) The fossils that possess the shortest subtending axes
may represent detached laterally borne dehiscent and reniform
sporangia, a diagnostic feature of zosterophylls. It is not possible
to produce a more precise determination of these specimens, due
to the fragmentary nature of the material.
The presence of a central strand in some axes, interpreted as
vascular on the basis of size and shape of the observable in situ cell
outlines can either be part of plants with rhyniophytoid architec-

ture and dehiscent sporangia or of zosterophylls. Zosterophylls
are known to possess G-type tracheids and some of the plants with
rhyniophytoid architecture and dehiscent sporangia have been
demonstrated to be vascular as well (Li, 1992).
On the contrary, the seven occurrences of K-type branchings
shed little doubt on the actual presence of zosterophylls. Even

though those branchings are not an ‘‘official’’ diagnostic character
of zosterophylls, they have hitherto only been recorded as part of
zosterophylls, when not dispersed. Therefore the flora includes
two major components: (1) plants with rhyniophytoid architecture
and reniform and/or dehiscent sporangia, which are likely to be a
stem-group of zosterophylls; and (2) zosterophylls.
The plants bearing the lateral structures resembling microphylls could also share affinities with lycophytes sensu lato.
More derived plants, i.e. plants with euphyllophytes affinities,
have possibly been present in the flora, as suggested by the lateral
branching systems. Minute plants with lateral fertile systems have
recently been discovered in the Late Silurian of North China (Wang
et al., 2007).
5.1.3. Locality 4
It is also impossible to deduce a floral composition because of
the fragmentary preservation. The flora includes large plants with
fibrous stem.
5.1.4. Locality 5
Plant remains, all considered as belonging to the same taxon,
found in locality 5 are comprised of thick axes that branch anisotomously at 120°, and more slender dichotomous systems. The
slender vegetative dichotomous systems are most likely the continuation of the lateral branches of the thicker axes. Indeed, the
thick axes lateral emissions width is comparable to that of the basal internodes of the dichotomous systems. On the specimen
ST390-20, the larger axes and the slender isotomous systems are


P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

59

Fig. 7. Global palaeogeography of the Late Silurian. Squares: location of floras from the Khazakhstanian unit; circles: floras from the South Laurussian–Northwest Gondwanan
unit; triangle: flora from Bathurst Island; star: flora from the Australian unit; rhomb: flora from the Dô Son peninsula (modified from Raymond et al., 2006).

connected. The plant can thus be understood as main axes that
bear lateral, helicoidally-arranged, ramified vegetative systems.
This fits the definition of euphyllophytes (Kenrick and Crane,
1997). The gross morphology of the plant indeed strongly recalls
that of some basal euphyllophytes, especially Psilophyton Dawson
1859. Similar branchings, axes width and terminal vegetative
recurvations are present in Psilophyton dawsonii (Banks et al.,
1975). Yet we prefer not to name that plant, and refer it to a ‘‘basal
euphyllophyte’’, since no sporangia can allow its precise taxonomic
attribution, nor warrant the erection of a new taxon. This basal
euphyllophyte is dominant in the assemblage of Ngoc Vung Island,
which may even be monospecific.
5.2. Stratigraphic bearings of the plant findings
Plants are generally, but unjustly, regarded as poor biostratigraphic tools for the Siluro-Devonian period. The fossil record is
scarce and characterized by provinciality (Raymond et al., 2006),
which may generate biases. Nonetheless, the morphological and
anatomical characters of the early land plants show remarkably rapid changes throughout the Devonian, so that their biostratigraphic potential has been pointed out (Edwards and Davies,
1990). A biostratigraphic method, based on characters, rather than
taxa, was developed by Gerrienne and Streel (1994). Unfortunately
our fossils display too few anatomical characters to apply here.
However, since the stratigraphy of the Siluro-Devonian of the
Quang Ninh area needs to be refined, we consider that their stratigraphic bearings are worth to be mentioned.
The very tiny plants fragments from locality 1 (Van Canh Fm)
suggest a Late Silurian age. Early Devonian axes are usually larger
indeed. Size is not a widely used criterion for stratigraphy, but concerning plants, a relationship between axes size and sediment age
is clearly established for the Silurian and Devonian (Edwards,
1979; Gerrienne, 1990; Gerrienne and Streel, 1994). The plants
from localities 2 and 3 (Van Canh Fm) are mostly zosterophylls
and plants with terminal reniform sporangia, which are characteristic of Upper Silurian–Lowermost Devonian proximal deposits.

This is consistent with the faunal data, which suggest a Late Silurian age for the Dô Son outcrops.
The large fibrous stem recovered at locality 4 is younger. The
oldest plant displaying axis around 1.5 cm thick is Pertica Kasper
and Andrews, 1972. Pertica is a basal euphyllophyte from the Trout
Valley Formation, Maine, USA, which is LateEmsian–Early Eifelian
in age (Kasper and Andrews, 1972). This is consistent with
Nguyen’s dating (2007) for the Duong Dong Formation, which is
supposed to be Eifelian. The basal euphyllophyte remain found at
locality 5 is also consistent with an Eifelian age. However, basal
euphyllophytes (i.e. with lateral vegetative systems) with such
axes width (3–4 mm) are more characteristic of the Emsian (Gerrienne, 1990; Gerrienne and Streel, 1994). Therefore, the exposure of
the Duong Dong Fm on Ngoc Vung island is possibly of Emsian age,
all the more that the Duong Dong Fm is likely to be diachronic (Janvier et al., 2003). This strengthens the hypothesis stating that the
stratigraphic extension of the Duong Dong Formation may therefore be more important than previously thought (Nguyên et al.,
2007; Tong et al., Pragian), encompassing accepted for publication
to Eifelian sediments.
5.3. Comparisons
5.3.1. Comparison with other Late Silurian floras
Raymond et al. (2006) produced a global phytogeographic analysis of Late Silurian macrofloras. The authors led two analyses: one
based on taxa and another based on morphological traits. Both
analyses yielded the same four phytogeographic units, ensuring
that the definition of areas is not biased by regional taxonomic
usage. The phytogeographic units are (1) Bathurst Island, (2) a
South Laurussian–Northwest Gondwanan assemblage, (3) an East
Gondwanan assemblage (Australia), and (4) a Khazakhstanian
assemblage. We will now briefly compare our South Chinese block
assemblage to each Late Silurian phytogeographic unit (Fig. 7).
More importance will be given to the Khazakhstanian flora, as it
is the closest assemblage to South China, in terms of

palaeogeography.


60

P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

5.3.1.1. Flora from the Pridoli of Khazakhstania: data from the
Wutubulake Formation of China. The Wutubulake flora is coeval to
that of the Van Canh Formation at Dô Son. However Wutubulake
was part of the Khazakhstanian block (Edwards, 1990; Edwards
et al., 2001). Khazakhstania was located on the equatorial belt of

the Gondwana (Scotese, 2010). The South China block, to which belongs the Dô Son plant remains outcrop, is supposed to be a perigondwanan terrane, i.e. it was possibly closer to the Gondwana
in Silurian-Devonian times. Plants showing rhyniophytoid architecture with reniform sporangia were present in both terranes, as

Table 1
Composition of Late Silurian–Early Devonian plant assemblages from southeastern Asia.
Van Canh Fm flora

Watabulake Fm flora

Xujiachong Fm flora

Posongchong Fm flora

(Late Silurian)

(Late Silurian)

(Pragian)

(Pragian)

Vietnam

China

China

China

Plants at a bryophyte grade
of organization

Sporogonites cf.
S.yunnanense

Plants with a rhyniophytoid
architecture

At least three taxa,
possibly including
Aberlemnia sp.

Lycophytina sensu Kenrick and
Crane (1997) or plants with
lycophytes affinities

Zosterophylls

indet.

Duong Dong
Fm flora
(? Emsian–?
Givetian)
Vietnam

Sporogonites
yunnanense (Hsü,
1966)
Junggaria spinosa (Cai
et al., 1993)

Hsüa robusta (Li, 1992)

Salopella xinjiangensis
(Cai et al., 1993)
Sciadophyton sp. (Cai
et al., 1993)

Hsüa deflexa (Wang
et al., 2003)

Zosterophyllum sp.
(Cai et al., 1993)

Zosterophyllum
australianum (Hao,
1992)

Zosterophyllum
yunnanicum (Wang,
2007)
Zosterophyllum longa
(Wang, 2007)
Huia gracilis (Wang
et al., 2002)
Drepanophycus
qujingensis (Li and
Edwards, 1995)
Bracteophyton
variatum (Wang and
Hao, 2004)
Guangnania cuneata
(Wang and Hao, 2002)

Baragwanathia sp. (Hao and
Gensel, 1998)
Zosterophyllum australianum
(Hao and Gensel, 1998)
Zosterophyllum sp.1 (Hao and
Gensel, 1998)
Huia recurvata
Gumuia zyzzata (Hao, 1989b)

Adoketophyton subverticillatum
(Li and Edwards, 1992; Hao
et al., 2003)
Discalis longistipa (Hao, 1989a)
Stachyophyton yunnanense

(Geng, 1983; Wang and Cai,
1996)
Wenshania zhichangensis (Zhu
and Kenrick, 1999)
Guangnania cuneata (Wang and
Hao, 2002)
Hueberia zhichangensis (Yang
et al., 2009)
Zenghlia radiata (Hao et al.,
2006)
Halleophyton zhichangense (Li
and Edwards, 1997)
Demersatheca contigua (Li and
Edwards, 1996)

Basal euphyllophytes sensu Kenrick and
Crane (1997) or plants with
euphyllophyte affinities

Probably at least
one taxon

Psilophyton primitivum (Hao and
Gensel, 1998)

Watabulaka
multidichotoma
(Wang et al., 2007)

Eophyllophyton bellum (Hao and

Beck, 1993)
Polythecophyton demissum (Hao
et al., 2001)
Plant with sphenopsid affinities
Plant of unknown affinities

Estinnophyton yunnanense (Hao
et al., 2004)
cf. Filiformorama
sp.

Filiformorama
simplexa (Wang et al.,
2006)

Hedeia sinica (Wang
et al., 2002)

Hedeia sinica (Hao and Gensel,
1998)
Celatheca beckii (Hao and Gensel,
1995)
Catenalis digitata (Hao and Beck,
1991b)
Yunia dichotoma (Hao and Beck,
1991a)

Basal
euphyllophyte

P. Gonez et al. / Journal of Asian Earth Sciences 43 (2012) 51–63

well as early lycophytes with K-type branchings (Table 1). The
enigmatic taxon Filiformorama is also common to both floras. The
originality of the Wutubulake formation flora lies in the early presence of plants with lateral fertile systems (Wang Yi et al., 2007).
The Van Canh formation flora also delivers plants with lateral
branchings systems, but it is impossible to tell whether they were
vegetative or fertile, and their affinities therefore remain unresolved. These two floras respectively belong to two different phytogeographic sub-units (Hao and Gensel, 1998), but may have
been somewhat linked, according to the dispersed morphological
features mentioned above. This hypothesis of the relationship between the floras of the two terranes must be considered with caution, mainly for two reasons: (1) the fragmentary nature of the
Vietnamese plants does not allow fully reliable comparisons, (2)
the Wutubulake Fm flora is also characterized by taxa with rhyniophytoid architecture with non-reniform sporangia (Table 1). This
constitutes a major difference from the South Chinese phytogeographic unit, to which the Dô Son, Posongchong and Xujiachong
floras belong.
5.3.1.2. Floras from South Laurussia–Norwest Gondwana. This phytogeographic unit is mostly documented by Welsh and South American floras. It is characterized by the dominance of plants of
rhyniophytoid architecture (Raymond et al., 2006), some of them
exhibiting reniform dehiscent sporangia (Edwards, 1970; Edwards
et al., 2001; Gonez and Gerrienne, 2010a); and the occasional presence of zosterophylls. Our assemblage also contains occasional
zosterophylls and plants of rhyniophytoid architecture, with reniform and dehiscent sporangia, Aberlemnia-type. The major difference between the two assemblages lies in the presence of a large
panel of rhyniophytoids with non reniform sporangia in the South
Laurussian–Northwest Gondwanan assemblage. However, this difference may be the result of sample bias, as only one Silurian locality is known on the South China block, whereas numerous sites
have been prospected in Wales and South America.
5.3.1.3. Flora from the Ludlow of Bathurst Island. The assemblage of
Bathurst Island is represented by seven taxa, the majority of which
are zosterophylls. The plants are remarkably complex and derived
in regard of their old age (Kotyk et al., 2002). Our assemblage differs neatly from that of Bathurst Island: more basal embryophytes
well represented on the South China block flora. Thus the Canadian
flora remains unique.
5.3.1.4. Flora from East Gondwana: data from Australian assemblages. The Australian assemblage is also dominated by Lycophytes

sensu lato (Baragwanathia and Zosterophyllum), together with plant
with rhyniophytoid architecture and non reniform sporangia (Salopella) and the possibly more derived plant Hedeia (Raymond et al.,
2006). Therefore this assemblage is radically different from our
South Chinese flora.
5.3.2. Comparison with younger floras from the South China block:
data from the Pragian Posongchong and Xujiachong Formations, China
The Xujichong and the Posongchong formations floras are from
the South China block. They are younger than the Dô Son flora and
are dominated by lycophytes (64% of the number of taxa in each
case) (Table 1). It is worth to notice that plants with ‘‘rhyniophytoid’’ architecture are also present in the Xujiachong Fm and display reniform, bivalved and dehiscent sporangia (Table 1), like
the ‘‘rhyniophytoid’’ plants from Dô Son. The Dô Son fossils therefore suggest that the Late Silurian flora of the South China block
was roughly similar to the younger Pragian floras of the same terrane, i.e. comprised of plants with rhyniophytoid architecture and
reniform sporangia, early lycophytes and, occasionally, more derived plants (Table 1).

61

The presence of a basal euphyllophyte in the ?Emsian-?Eifelian
of the South China block (the Duong Dong Fm/Ngoc Vung Island
flora, locality 5) is also consistent with the Chinese data. Indeed basal euphyllophytes are represented by three taxa in the Posongchong Fm flora, including a species of Psilophyton (Table 1).
6. Conclusions
(1) The fossil plants from the Dô Son peninsula in northern Vietnam likely represents the oldest flora of the South China
Block they indicate that the land flora of this major Asian
land mass was already fairly diverse at least since the Late
Silurian. This is in agreement with data from Ludlow, Pridoli
and earliest Lochkovian plant localities all over the world
(Edwards, 1979; Tims and Chambers, 1984; Cai et al.,
1993; Edwards et al., 2001; Gerrienne et al., 2001; Kotyk
et al., 2002). The early flora of the South China block was
mainly comprised of early lycophytes and plants with rhyniophytoid architecture and reniform sporangia. Some more
derived and/or enigmatic plants are also encountered. This

composition is qualitatively similar to the younger Pragian
assemblages from the Yunnan Province, southern China.
The Pragian flora of Yunnan might thus have been established on the South China block since the Late Silurian. It is
however frustrating that the fragmentary nature of the fossils only allows to infer a global floral composition of the
vegetation. More field work is needed in order to investigate
new localities with better preserved fossils, which could
allow a more accurate taxonomic and palaeobiological
considerations.
(2) The stratigraphic significance of the plant remains in the
Ngoc Vung series is in concordance with the previous data
for the Van Canh Formation and agrees with the Late Silurian
(probably Pridoli) age of the plant-bearing outcrop inferred
from faunal data. Concerning the Duong Dong Formation,
the plant remains strengthen the hypothesis of a broader
age range that could also encompass Pragian to Eifelian
sediments.

Acknowledgments
We thank Mme Marcela Giraldo for the preparation of the palynological samples, Dr. Philippe Gerrienne for his advice and pertinent critics. We also thank an anonymous reviewer whose
comments substiantially improved the content of this manuscript.
The field work was made possible by National Geographic Grant
#8550-08. Ta Hoa Phuong has been supported by the Vietnamese
NAFOSTED (Project 105.01.79.09 and 105.06.60.09). Paul Gonez
holds a FRIA Grant.
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