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The earliest fossil bamboos of China (middle Miocene, Yunnan) and theirbiogeographical importance
Li Wang, Frederic M.B. Jacques, Tao Su, Yaowu Xing, Shitao Zhang,Zhekun Zhou
PII: S0034-6667(13)00110-3DOI: doi: 10.1016/j.revpalbo.2013.06.004Reference: PALBO 3472
To appear in: Review of Palaeobotany and Palynology
Received date: 15 February 2013Revised date: 22 June 2013Accepted date: 25 June 2013
Please cite this article as: Wang, Li, Jacques, Frederic M.B., Su, Tao, Xing, Yaowu,Zhang, Shitao, Zhou, Zhekun, The earliest fossil bamboos of China (middle Miocene,Yunnan) and their biogeographical importance, Review of Palaeobotany and Palynology(2013), doi: 10.1016/j.revpalbo.2013.06.004
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The earliest fossil bamboos of China (middle Miocene, Yunnan) and their
biogeographical importance
Li Wanga, c
, Frédéric M. B. Jacquesa, Tao Su
a, Yaowu Xing
d, Shitao Zhang
e,
Zhekun Zhoua, b*
aKey Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical
Garden, Chinese Academy of Sciences (CAS), Mengla 666303, China
bKey Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany,
CAS, Kunming 650204, China
cState Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of
Geology and Palaeontology), CAS, Nanjing 210008, China
dInstitute of Systematic Botany, University of Zürich, Zürich, 8008, Switzerland
eFaculty of Land Resource Engineering, Kunming University of Science and
Technology, Kunming 650093, China
*Author for correspondence: Zhekun Zhou, [email protected]
Tel and Fax: +86-871-5219932
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Abstract
Fossil bamboo leaf blades and culms from the middle Miocene deposits of
Sanzhangtian, Zhenyuan County, Yunnan, Southwest China are reported for the first
time. The distinctive pseudopetioles and parallelodromous venation patterns of the
leaf blades and the nodal morphology of the culms support the placement of the
fossils into Poaceae subfamily Bambusoideae. We describe one new genus and four
new species. Bambusium angustifolia L. Wang et Z.K. Zhou, sp. nov. has leaf blades
0.7–1.6 (1.27) cm in width with 3–6 (4) lateral veins on both sides of the midrib. Leaf
blades of Bambusium latifolia L. Wang et Z.K. Zhou, sp. nov. are 1.4–3.8 (2.16) cm
wide with 4–7 (6) lateral veins on both sides of the midrib. Culms of Bambusiculmus
latus L. Wang et Z.K. Zhou, sp. nov. have an internodal external diameter of 1.6–2.9
(2.5) cm, and more or less horizontal nodal line and supranodal ridge, while culm of
Bambusiculmus angustus L. Wang et Z.K. Zhou, sp. nov. has an internodal external
diameter of only 1.5 cm, and horizontal supranodal ridge and oblique nodal line. Our
findings provide the earliest evidence of bamboo fossil leaf blades and culms with
detailed external morphological characters in China. These fossils indicate that
bamboos in Yunnan began to diversify no later than the middle Miocene. Because
Yunnan is one of the biodiversity centers of modern bamboos, these fossils provide
new insights into bamboo biogeography.
Keywords: Bamboo fossil record; Bambusiculmus; Bambusium; biogeography;
middle Miocene; Yunnan
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1. Introduction
Of the 12 Poaceae subfamilies, Bambusoideae is one of the largest (Soreng et al.,
2012), and currently includes 115 genera with1439 described species (Bamboo
Phylogeny Group (BPG), 2006, 2012). The monophyly of Bambusoideae is supported
by molecular phylogenetic studies and three tribes are recognized within the
subfamily: Arundinarieae (temperate woody bamboos), Bambuseae (tropical woody
bamboos), and Olyreae (tropical herbaceous bamboos) (BPG, 2012; Kelchner and
BPG, 2013). Bamboos occur on all continents except Europe and Antarctica
(Soderstrom and Calderon, 1979; Sungkaew et al., 2009). Temperate woody bamboos
are highly diverse in East Asia with complex morphological features and diverse
habitats (Li, 1999; Ohrnberger, 1999). Temperate woody bamboos exhibit a
distribution typical of the eastern Asia–eastern North America disjunction (Triplett
and Clark, 2010). New World and Old World tropical woody bamboos are recognized
as independent clades according to molecular evidence (Kelchner and Clark, 1997;
Guo and Li, 2002; Kelchner and BPG, 2013).
The diversity of woody bamboos in Yunnan Province, southwestern China, is one
of the highest in the world, both at the community and species levels (Li and Xue,
1997; Yang et al., 2004). Most of the bamboo vegetation types, ranging from tropical
to subtropical, temperate and alpine, are found in Yunnan (Hsueh and Jiang, 1986).
Twenty-nine genera and 250 species of bamboos grow in Yunnan, which represent
three quarters of all genera and half of all species of Chinese bamboos (Yang et al.,
2004). Both Arundinarieae (for example, Chimonobambusa Makino, Fargesia
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Franchet) and Bambuseae (for example, Cephalostachyum Munro, Dendrocalamus
Nees, Gigantochloa Kurz ex Munro, Schizostachyum Nees, Thyrsostachys Gamble)
are represented in Yunnan (Li and Xue, 1997; Li et al., 2006).
The biogeography, diversification and origin of the Bambusoideae have been the
subject of numerous studies (Clark, 1997; Bouchenak-Khelladi et al., 2010;
Hodkinson et al., 2010; Triplett and Clark, 2010; Ruiz-Sanchez, 2011). Fossil
evidence can provide new insights into the phylogeny and biogeography of
Bambusoideae, but reliable fossil records of Bambusoideae are rare, especially in
China despite their modern-day species richness and wide distribution. A long fossil
history of bamboo exists in South America (Frenguelli and Parodi, 1941; Brea and
Zucol, 2007). The earliest reliable macrofossils of bamboo are from the Eocene of
Argentina (Frenguelli and Parodi, 1941). The earliest evidence of bamboo phytolith is
from the late Eocene deposit in North America (Strömberg, 2004, 2005). Worobiec
and Worobiec (2005) summarized the occurrences of fossil bamboos in Europe: the
earliest macrofossil of bamboos in Europe is from the Oligocene of Italy (Peola,
1900). There are no records of Bambusoideae fossils from Africa or from the
Holocene of Europe. Bamboo fossils from Asia are reported from Nepal (Awasthi and
Prasad, 1990), Japan (Miki, 1941; Ozaki, 1980) and Indonesia (Heer, 1883). There is
only one unquestioned report of a bamboo fossil from China, a fusinized fossil culm
from the Pliocene of Xundian County, central Yunnan (Li et al., 2008). Two bamboo
fossils were recorded from Neogene floras in Zhejiang, eastern China (Li, 1984) and
Taiwan (Chaney and Chuang, 1968), but without any detailed descriptions and figures
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to confirm their placement in Bambusoideae. It is not clear whether the prevalence of
extant Chinese bamboos corresponds to a recent diversification event or whether
bamboos have been present in China for a long time but without a clear fossil record.
Recently, numerous well-preserved leaf blades and culms were discovered from
the middle Miocene deposits in Sanzhangtian Basin, Zhenyuan County, Yunnan,
Southwestern China. The material described herein represents the earliest bamboo
fossil leaf blades and culms from China, with detailed external morphologies. We
propose one new genus and four new species, and the importance of these new
findings on bamboo biogeographical history are discussed.
2. Material and methods
2.1. Fossil locality and geological settings
Specimens were collected from Sanzhangtian, Zhenyuan County, central Yunnan,
Southwestern China (24°06' N, 101°13' E) (Fig. 1). The Neogene deposits in
Sanzhangtian belong to the Dajie Formation, and this formation is dated as middle
Miocene (Ge and Li, 1999; Zhang et al., 2012) based on stratigraphic studies. Two
sedimentary facies are recognized in the fossil-bearing clay: a lower fluvial facies and
an upper lacustrine facies (Fig. 2; Fig. 3). Most of the bamboo fossil leaf blades and
culms were found in the grey-white or white layers at the upper part of the fluvial
facies (Fig. 2; Fig. 3). The rests are found in the carbonaceous mudstones and
calcareous mudstones in the lacustrine deposits (Fig. 2; Fig. 3).
2.2. Fossil materials and morphological measurements
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Our descriptions are based on forty-four well-preserved compression and
impression fossil leaf blades. These fossil leaf blades include 21 leaf blades from
“layer 21” and 23 leaf blades from “layer 19” in the fluvial deposits (Fig. 3). The
epidermis was preserved on almost all compression leaf blades, but lacked clear cell
morphologies. Culms were mostly preserved as compressions. Some culms were
preserved as cast.
Measurements were made using ImageJ (http://rsb.info.nih.gov/ij/) and a vernier
calliper. If only half of a leaf blade is preserved, the width of the leaf blade is
measured as twice the width of the half leaf blade. We measured vein density
following Field et al. (2011) using the length of veins per unit of leaf blade area (mm
mm−2
). Statistical analyses were carried out in the R package. The macromorphology
and micromorphology of the fossils were photographed with a Nikon D700 camera,
and studied under a stereo microscope (S8APO Leica) or a microscope (DM750 Leica)
coupled with digital cameras. Some specimens were immersed in aviation fuel in
order to enhance the contrasts. All fossil materials and epidermis slides are kept in
Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences.
2.3. Terminology
Leaf blade and culm terminology of both fossil and living bamboos follows
Metcalfe (1960), Wu (1961), Soderstrom and Young (1983), Worobiec and Worobiec
(2005) and Brea and Zucol (2007) (Fig. 4).
3. Systematics
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Order: Poales Small 1903
Family: Poaceae Barnhart 1895
Subfamily: Bambusoideae Luerssen 1893
Bambusium Unger 1845
Bambusium angustifolia L. Wang et Z.K. Zhou, sp. nov.
Holotype: SZT0001-1 (Plate I, 1).
Paratypes: SZT0001-3, SZT0001-4, SZT0001-11, SZT0003-1, SZT0003-3,
SZT0005-1 (Plate I, 3–6; Plate II, 1–3); slides: SZT-S-0001 (Plate II, 4).
Repository: Xishuangbanna Tropical Botanical Garden, Chinese Academy of
Sciences, China.
Type locality: Sanzhangtian coal-bearing basin (24°06' N, 101°13' E), Zhenyuan
County, central Yunnan, China.
Type stratum: Dajie Formation.
Age: middle Miocene.
Etymology: The specific epithet, angustifolia, was chosen for the narrow leaf
blades.
Diagnosis: Leaf blades small and narrow; base cuneate; pseudopetiole narrow;
leaf blade margin entire or loosely serrate with fine teeth; macro-hairs occasional; 3–6
(4) lateral veins on both sides of the midrib; 5–8 (6 or 7) third order parallel veins
between lateral veins.
Description: The specimens are compression and impression fossil leaf blades
(Plate I, 1, 3–6). Most leaf blades are incomplete. Leaf blades are linear, lanceolate to
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elongate, up to 10.5 cm long and 0.7–1.6 (1.27) cm wide. Two almost entire leaf
blades are 8 and 9.5 cm long (Plate I, 3–4). The apex is attenuate (Plate I, 3–4).
Pseudopetioles are narrow and approximately 1 mm wide and 2 mm long (Plate I, 1).
Leaf blade bases are cuneate, decurrent on pseudopetioles (Plate I, 1). Venation
pattern is parallelodromous. Midrib is distinct, and generally projects on the abaxial
surface. On both sides of the midrib there are 3–6 (4) less distinct lateral veins spaced
0.86–2.23 (1.27) mm apart (Plate I, 1, 3–4, 6; Plate II, 1). There are 5–8 (6 or 7)
delicate, third order parallel veins spaced 0.12–0.27 (0.19) mm apart between adjacent
lateral veins (Plate II, 1). Cross veins connect adjacent parallel veins (Plate II, 1). The
cross veins and third order parallel veins form a tessellate venation pattern. Adjacent
cross veins are spaced 0.35–1.07 (0.61) mm apart, slightly oblique or perpendicular to
the third order parallel veins (Plate II, 1, 4). Vein densities are 5.78–10.11 (7.06) mm
mm-2
. Leaf blade margins are entire or loosely serrate with fine teeth spaced 520–380
µm apart, at an angle of 45° or less from the margin (Plate II, 2). In some leaf blades,
macro-hairs 82–141 μm long occur in the intercostal zones or near the third order
parallel veins (Plate II, 3). Numerous small black dots with a diameter of 13.6–22.7
μm are more commonly found on both sides of the third order parallel veins (Plate II,
3); these dots are most likely prickle-hairs or prickle-hair bases. Bands of probable
bulliform cells lie between two adjacent third order parallel veins (Plate II, 4).
There are also many larger dark spots with a diameter of 44–103 μm on the
epidermis (Plate II, 1, 4). They are possible epiphyllous fungi. Leaf blade damage by
pathogens (Plate I, 5) is similar to those found in modern samples (Plate IV, 7).
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Bambusium latifolia L. Wang et Z.K. Zhou, sp. nov.
Holotype: SZT0009b-1 (Plate III, 1).
Paratypes: SZT0009a-7, SZT0009b-2, SZT0010a, SZT0010a-1, SZT0010a-2,
SZT0010a-3, SZT0010a-5, SZT0010a-8, SZT0010a-10, SZT0010a-14, SZT0010b-8,
SZT0010b-15, SZT0011-5 (Plate III, 2–6; Plate IV, 1–6).
Repository: Xishuangbanna Tropical Botanical Garden, Chinese Academy of
Sciences, China.
Type locality: Sanzhangtian coal-bearing basin (24°06' N, 101°13' E), Zhenyuan
County, central Yunnan, China.
Type stratum: Dajie Formation.
Age: middle Miocene.
Etymology: The specific epithet, latifolia, was chosen for the broad leaf blades.
Diagnosis: Leaf blades mostly large and wide; base cuneate or obtuse;
pseudopetiole wide and long in branch leaf blades, very short in culm leaf blades; 4–7
(6) lateral veins on both sides of the midrib; 5–9 (7) or occasionally 3–5 third order
parallel veins between lateral veins.
Description: The specimens are compression and impression fossil leaf blades
(Plate III, 1–6). Most leaf blades are incomplete. Leaf blades are linear, lanceolate to
elongate. The apex is attenuate (Plate III, 6). Leaf blade bases are cuneate or obtuse,
decurrent on pseudopetioles (Plate III, 1–5). Venation pattern is parallelodromous.
Branch leaf blades are 1.4–3.8 (2.16) cm wide. Fragmentary leaf blades are up to
12.5 cm long. Pseudopetioles are about 2–4 mm long and 2 mm wide (Plate III, 1, 4).
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Midrib is distinct, and generally projects on the abaxial surface. There are 4–7 (6) less
distinct lateral veins on both sides of the midrib spaced 1.29–3.07 (1.87) mm apart
(Plate III, 1, 4–6; Plate IV, 1). There are 5–9 (7) delicate, third order parallel veins
spaced 0.18–0.42 (0.24) mm apart between adjacent lateral veins (Plate IV, 1–2, 6).
Cross veins connect adjacent parallel veins. The cross veins and third order parallel
veins form a tessellate venation pattern. Adjacent cross veins are spaced 0.26–1.02
(0.57) mm apart, oriented slightly oblique or perpendicular to the third order parallel
veins (Plate IV, 1–2, 6). Vein density is 4.64–7.63 (5.84) mm mm-2
. The presence of
teeth on leaf blade margins is not obvious. Numerous small black dots with a diameter
of 17.6–25.7 (20.1) μm are more commonly found along the intermediate line of the
intercostal zones between two adjacent third order parallel veins (Plate IV, 3). They
are most likely prickle-hairs or prickle-hair bases.
There are also many larger dark spots with a diameter of 64.7–108.8 μm on the
epidermis of branch leaf blades (Plate IV, 1, 6). They are possible epiphyllous fungi.
Many pathogen-damaged areas were observed on some branch leaf blades (Plate III,
5–6; Plate IV, 5), and are similar to modern examples (Plate IV, 7).
Two culm leaf blades are 1 and 2.2 cm wide. Pseudopetioles are very short and
wide, and about 1–1.5 mm long and 2–3 mm wide (Plate III, 2–3). Midrib is not
distinct especially in the smaller leaf blade. On both sides of the midrib there are 6
less distinct lateral veins spaced 0.88–1.91 (1.42) mm apart (Plate III, 2–3). There are
3–5 (4–5) delicate, third order parallel veins spaced 0.22–0.34 (0.27) mm apart
between adjacent lateral veins (Plate III, 2–3). Numerous small black dots with a
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diameter of 12.8–19.2 (16.8) μm are found on both sides of the third order parallel
veins (Plate IV, 4). They are most likely prickle-hairs or prickle-hair bases.
Bambusiculmus L. Wang et Z.K. Zhou, gen. nov.
Type: Bambusiculmus angustus L. Wang et Z.K. Zhou, sp. nov.
Diagnosis: Nodes and internodes conspicuous; nodal line and/or supranodal
ridge horizontal and/or oblique; remnant basal parts of the culm sheath sometimes on
nodal line; surface smooth or sulcate.
Etymology: The new genus is named for bamboo fossil culms.
Bambusiculmus latus L. Wang et Z.K. Zhou, sp. nov.
Holotype: SZT0012a-1, SZT0012b-1 (Plate V, 1–4).
Paratypes: SZT0012a-2, SZT0012a-3, SZT0012b-2, SZT0012b-3 (Plate V, 1–2).
Repository: Xishuangbanna Tropical Botanical Garden, Chinese Academy of
Sciences, China.
Type locality: Sanzhangtian coal-bearing basin (24°06' N, 101°13' E), Zhenyuan
County, central Yunnan, China.
Type stratum: Dajie Formation.
Age: middle Miocene.
Etymology: The specific epithet “latus” refers to the wide feature of these fossil
bamboo culms.
Diagnosis: Culm thick; internodal external diameter around 2.5 cm; nodal line
and supranodal ridge both more or less horizontal; surface smooth.
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Description: The specimens are compression, impression and cast of fossil culms
(Plate V, 1–4). Culms are incomplete. Culms have conspicuous nodes and internodes.
Each specimen has one conspicuous node and two incomplete internodes, with an
internodal external diameter of 1.6–2.9 (2.5) cm. The nodes have a diameter of about
3 cm and a length of about 0.8 cm. Buds are not observed. The lowermost boundary
of the node is the nodal line and the uppermost boundary of the node is the supranodal
ridge (Plate V, 3–4). The nodal region is somewhat concave. The nodal line or sheath
scar and the supranodal ridge are horizontal. The supranodal ridge area is more or less
swollen. Culm surface is usually smooth. The incomplete internode is up to 14 cm
long.
Bambusiculmus angustus L. Wang et Z.K. Zhou, sp. nov.
Holotype: SZT0013a, SZT0013b (Plate V, 5–8).
Repository: Xishuangbanna Tropical Botanical Garden, Chinese Academy of
Sciences, China.
Type locality: Sanzhangtian coal-bearing basin (24°06' N, 101°13' E), Zhenyuan
County, central Yunnan, China.
Type stratum: Dajie Formation.
Age: middle Miocene.
Etymology: The epithet “angustus” refers to the thin feature of these fossil
bamboo culms.
Diagnosis: Culm thin, internodal external diameter about 1.5 cm; supranodal
ridge more or less horizontal; nodal line oblique; remnant basal parts of the culm
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sheath on nodal line; surface sulcate, especially on and above supranodal ridge.
Description: The specimens are compression and impression fossil culms (Plate
V, 5–8). Culms are incomplete. The culm has conspicuous nodes and internodes. The
culm is hollow in the internode area (Plate V, 5). The specimen has one conspicuous
node and two incomplete internodes, with an internodal external diameter of about 1.5
cm of the culm. The node has a diameter of 1.6 cm and a length of 0.5 cm. Buds are
not observed. The lowermost boundary of the node is the nodal line and the
uppermost boundary of the node is the supranodal ridge (Plate V, 5–8). The nodal
region is concave near the nodal line. The nodal line is oblique, bearing remnant basal
parts of the culm sheath (Plate V, 7–8). The supranodal ridge area is swollen and the
supranodal ridge is more or less horizontal. Culm surface is sulcate especially at and
above the supranodal ridge (Plate V, 6–8). The incomplete internode is up to 8 cm
long.
4. Discussion
4.1. Fossil Taxonomy
The presence of deciduous leaf blades and pseudopetioles is the synapomorphy
of the woody bamboos (Soderstrom and Ellis, 1987; Geng and Wang, 1996; Grass
Phylogeny Working Group (GPWG), 2001; Plate I, 2). The fossil leaf blades from the
Miocene of Sanzhangtian are assigned to Bambusoideae due to the presence of a
pseudopetiole along with the linear, lanceolate to elongate leaf blade shape and
parallelodromous venation patterns.
In Poaceae, leaf blades of several genera such as Phragmites (subfamily
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Arundinoideae), Arundo (subfamily Arundinoideae), Neyraudia (subfamily
Chloridoideae) and Thysanolaena (subfamily Panicoideae) are similar to bamboo leaf
blades in their general shape or venation pattern, but their leaf blades lack a
pseudopetiole and pass directly into a sheath (Geng and Wang, 1996; personal
observation).
Although pseudopetioles are also present in other Poaceae (GPWG, 2001), such
as whole members of Anomochlooideae, Pharoideae and Puelioideae, some members
of Ehrhartoideae and Panicoideae, and very few members of Pooideae (GPWG, 2001),
these non-bambusoid grasses have leaf blades which lack the abscission layer in their
pseudopetioles. For example, the leaf blade of Lophatherum Brongniart, a member of
the Zeugiteae within the Panicoideae (Sánchez-Ken and Clark, 2010), has a
pseudopetiole and leaf blade shape and venation pattern similar to those of
Bambusoideae (personal observation), but Lophatherum is herbaceous and does not
lose leaf blades due to the lack of an abscission layer between the leaf blade and leaf
sheath and are unlikely to be preserved only as separated leaf blades, as is the case
with our specimens. Moreover, the leaf blade vein density in Lophatherum (2.85 mm
mm-2
) is much lower than that of the fossils (5.9 to 6.99 mm mm-2
).
Furthermore, these fossil bamboo leaf blades share other features with modern
bamboos, including (1) minute teeth on the leaf blade margins (Plate II, 2, 6), (2)
macro-hairs on the leaf blade epidermis (Plate II, 3, 5), (3) bands of bulliform cells
between two adjacent third order parallel veins (Plate II, 4, 7) and (4) probable
prickle-hairs or prickle-hair bases (Plate II, 3; Plate IV, 3–4). Among these features,
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the presence of bulliform cells is a synapomorphy for the Poaceae family (Metcalfe,
1960). The combined presence of pseudopetiole and such characteristics enables us to
confidently assign the fossil presented here to Bambusoideae.
The fossil culms are identified as Bambusoideae because they share features
characteristic of Poaceae stems and in particular Bambusoideae culms: they possess
conspicuous nodes and internodes, and conspicuous nodal lines and supranodal ridges
in the nodal regions. Although some non-bambusoid Poaceae genera have nodal lines
and supranodal ridges, these structures are always less conspicuous than in bamboos
(Keng, 1959).
Generic assignment of bamboo leaf blades based only on their morphological
and anatomical characteristics is difficult (Metcalfe, 1956; Soderstrom and Ellis, 1987;
Worobiec and Worobie, 2005). Because the identification of bamboos based only on
leaf blade or culm material is highly tentative, we place these fossil leaf blades in the
fossil genus Bambusium and the culms in the fossil genus Bambusiculmus instead of
assigning them to a specific modern genera.
Fossil bamboo culms are always preserved together with fossil bamboo leaf
blades in the same sediment layers in Sanzhangtian. However, because there were no
direct anatomic connections between the fossil leaf blades and culms described here,
we prefer to describe them as separate species. New discoveries and further studies
may help resolve their affinity.
4.2. Comparisons with other fossil species
The leaf blades of Bambusium angustifolia and B. latifolia differ remarkably
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from Bambusa ilinskiae Shvareva from the Miocene of the Precarpatians (Shvareva,
1970): the latter has broader leaf blades, and more lateral veins (Table 1).
Leaf blades of Sasa kodorica Kolakovsky from the Neogene of Kodor in
Abkhazia (Kolakovsky, 1964) are more than twice as wide as Bambusium angustifolia.
Sasa kodorica has similar leaf blade width to B. latifolia, but lacks venation
information. Sasa lugdunensis (Saporta) Givulescu, from a Neogene deposit in
Chiuzbaia, Maramures, Romania (Givulescu, 1984), has narrow leaf blades, and is
similar to B. angustifolia in size and the number of lateral veins, but has relatively
fewer third order parallel veins.
Bambusium sp. A from the late Miocene flora of Tatsumitoge in Honshu, Japan
(Ozaki, 1980) is not similar to the species from Sanzhangtian. It has larger leaf blades
than B. latifolia, and far more lateral veins from 7 to 10). In the same deposit in
Tatsumitoge, the size and numbers of veins in Bambusium sp. B are similar to B.
latifolia, but whether cross veins are present in the former is unknown. Bambusa sp.
from the Pliocene flora of Murat, Cantal, France (Roiron, 1991) has linear leaf blades
with leaf blade base attenuate into short pseudopetioles, which are similar to those of
Sanzhangtian fossil leaf blades, while the smaller leaf blades and fewer veins differ
from those of B. angustifolia. Leaf blades of Phyllostachys sp. from the upper
Miocene in Central Hondo, Japan (Miki, 1941) and B. angustifolia are similar in
width, but no further venation information is available.
Bambusium angustifolia from Sanzhangtian is most similar to “Bambusa”
lugdunensis Saporta (Worobiec and Worobiec, 2005) described from the upper
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Miocene of the Bełchatów Lignite Mine, Central Poland in size and vein numbers,
except for the cross vein space. The cross vein space of B. angustifolia is over twice
as long as “Bambusa” lugdunensis, thus the length/width ratio of the quadrangle
formed by cross veins and third order parallel veins of B. angustifolia is higher than in
“Bambusa” lugdunensis. Bambusa lugdunensis from the Pliocene of Asti, Piedmont,
Italy, has abruptly narrowed leaf blade bases (Martinetto, 2003), which is different
from our fossils which possess attenuate leaf blade bases into short pseudopetioles.
Few culm fossils with bambusoid affinities have been reported. Brea and Zucol
(2007) reported the first fossil record of petrified bamboo culms Guadua zuloagae in
the Pliocene Ituzaingó Formation, Argentina, which has both morphological and
anatomical features. Its internodal external diameter is 3.0–3.5 cm, which is larger
than in Bambusiculmus latus. Another fossil Guadua from the upper Pliocene–upper
Pleistocene in the southwestern Peruvian Amazon (Olivier et al., 2009) differs from
our fossil culms in its spiny or thorny structures at the node regions. The culm of
Phyllostachys sp. from the late Miocene deposit in Central Hondo, Japan (Miki, 1941)
is 1–1.4 cm broad, which is narrower than B. latus and B. angustus. The culm of
Bambusoideae sp. from the Pliocene deposit in Xundian County, Yunnan, possesses
Type-I vascular bundle (Li et al., 2008), but external morphological descriptions are
not available. Chusquea rolloti from Cenozoic sediments of Colombia has relatively
slender stems, large linear-lanceolate leaf blades and expanded rhizomal internodes
(Berry, 1929). Chusquea oxyphylla has a 7 cm long leaf blade impression with a culm
containing ten nodes covered by imbricated sheaths, where four leaf blades can be
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observed (Frenguelli and Parodi, 1941). Both of these Chusquea culms bear leaf
blades but have incomplete nodal and internodal information. In summary, based on
the lack of morphological and anatomical similarities with other fossil and extant
culms, we place fossil culms from Sanzhangtian into a new genus Bambusiculmus.
4.3. Biogeographical importance
Modern woody bamboos are distributed on all continents except Europe and
Antarctica, and their greatest diversity is in Southeast Asia and South America, where
they grow in various environments, such as tropical, subtropical, temperate and alpine
zones (Hodkinson et al., 2010; Fig. 5). To date, there are about 43 localities around
the world that have yielded fossil bamboos (Appendix; Fig. 5), though some fossils
described from these localities may not be bamboos. Most fossil bamboo localities
occur within the distributions of modern bamboos, especially in their greatest centers
of diversity, Southeast Asia and South America. However, some fossil bamboos (e.g.
European bamboo fossils) occur at latitudes further north than extant distributions
(Fig. 5).
The earliest reliable bamboo macrofossils are found from the Eocene of
Argentina (Frenguelli and Parodi, 1941), which is consistent with Clark’s (1997)
hypotheses that the earliest bamboos were of Gondwanan origin (southern
hemisphere). Consistent with the distribution of modern native bamboo taxa in South
America, fossil bamboo genera in the region are mainly neotropical woody bamboos,
such as Guadua (Brea and Zucol, 2007; Olivier et al., 2009; Brea et al., 2013).
European bamboo fossils occur from the Oligocene to the Pleistocene (Peola, 1900;
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Martinetto and Sami, 2001; Worobiec and Worobiec, 2005). The latest fossil bamboo
record from Europe is from the Pleistocene of Italy (Martinetto and Sami, 2001).
From then on, bamboos disappear from Europe, most likely because of Quaternary
glaciations (Ehlers and Gibbard, 2008). In Asia, bamboo fossils are found mainly in
the southern Himalayas to Japan from the late Miocene to Pliocene (Miki, 1941;
Ozaki, 1980; Awasthi and Prasad, 1990; Li et al., 2008). These regions also have a
rich diversity of modern temperate and paleotropical bamboos (Fig. 5). Pleistocene
Arundinaria fossils were found in southeastern North America (Berry, 1910; Brown,
1938), consistent with the occurrence of extant Arundinaria in North America (Fig. 5).
In Oceania, only two probable fossil bamboos are reported from the eastern coast of
Australia (Ettingshausen, 1887a) and from New Zealand (Ettingshausen, 1887b). In
these two areas there are no native modern bamboos. Modern Australian native
bamboos only occur on the northern coast of Australia (Franklin, 2008) (Fig. 5).
Although Africa has both modern palaeotropical and temperate woody bamboos
(Bystriakova et al., 2004; Sungkaew et al., 2009), there are no fossil bamboo records.
Our findings provide the earliest evidence of bamboo fossil leaf blades and
culms in China. The presence of bamboo fossils in Sanzhangtian indicates that
bamboos have occurred in Yunnan over a long geological history; a diversified fossil
bamboo forest or bamboo understory was already present during the middle Miocene
in Yunnan, the biodiversity center of modern bamboos in China. This ancient bamboo
forest or bamboo understory in an evergreen–deciduous forest accompanied by taxa
like Lauraceae, Alangium and Metasequoia (unpublished data) in Sanzhangtian
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potentially represents the environment in which Ailurarctos, one of the basal members
of the giant panda lineage found from the upper Miocene of Yunnan, China (Qiu and
Qi, 1989; Abella et al., 2012), could have lived.
Acknowledgements
This research was supported by grants from 973 Programme of MoST of China
(20120CB821901), National Natural Science Foundation of China (NSFC, No.
41030212, 41272007), XTBG Postdoctoral Research Funding (119103KP07), State
Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and
Palaeontology, CAS) (No. 123108). The authors thank the Herbarium, Kunming
Institute of Botany, CAS for supporting modern bamboo specimens and the
Herbarium of Xishuangbanna Tropical Botanical Garden, CAS for supporting
specimens of non-bambusoid Poaceae genera. We are grateful to J.J. Hu for collecting
modern bamboos from Ailao Mountain, Y.X. Zhang and S.J. Yang for discussion
about the temperate bamboos, B. Wen for identifying the modern bamboos, to J.C.
Liu for helping collecting fossils. The authors also thank H.J. Ma, C.Y. Zheng for
helping analysing the stratigraphy information; P. Kayaalp for revising the manuscript;
Z.P. Jing for helping in using the ArcGIS software; two anonymous reviewers for their
constructive suggestions and thorough comments on the manuscript.
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Figures and plates captions:
Fig. 1. 1, Study fossil locality; 2, close up of the site.
Fig. 2. Stratigraphic section of the fossil locality in Sanzhangtian. The sketches of
bamboo leaf blades and culms indicate the layers bearing fossils.
Fig. 3. Sedimentological stratigraphic section of the outcrop in Sanzhangtian. The
sketches of bamboo leaf blades and culms indicate the layers bearing fossils. The
Arabic numerals on the left of the two columns indicate the number of layers in each
sedimentary facies.
Fig. 4. Line sketch of the typical leaf blade shape, venation pattern and culm
morphology of modern bamboo. 1°, midrib, 2°, lateral vein, 3°, third order parallel
vein, 4°, cross vein.
Fig. 5. Geographical distribution of fossil and modern woody bamboos. Dots
represent fossil localities, and colours indicate geological ages (red, Paleogene; yellow,
Miocene; green, Pliocene; blue, Pleistocene; grey, Neogene; dark black, Cenozoic).
Modern woody bamboo distribution in fill colours or outlines: pink, paleotropical
woody bamboos; purple, neotropical woody bamboos; light blue outlines, temperate
woody bamboos. Modern woody bamboo distribution map is modified from
http://www.eeob.iastate.edu/research/bamboo/maps.html, with permission from Dr.
Lynn Clark.
Plate I. Leaf blades of Bambusium angustifolia (1, 3-6) and Arundinaria gigantea
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(Walt.) Muhl. (2).
1, Basal pseudopetiolate (black arrow) leaf portion, Holotype, SZT0001-1, scale bar =
10 mm;
2, A. gigantea leaf blade with a pseudopetiole (black arrow), KUN No. 0927028, scale
bar = 10 mm;
3, a nearly entire leaf blade, Paratype, SZT0005-1, scale bar = 10 mm;
4, a nearly entire leaf blade, Paratype, SZT0003-1, scale bar = 10 mm;
5, Leaf fragment with damaged areas by pathogens (white arrow), Paratype,
SZT0001-11, scale bar = 5 mm;
6, middle and basal part of a fossil bamboo leaf blade, Paratype, SZT0001-4, scale bar
= 10 mm.
Plate II. Micromorphology of Bambusium angustifolia (1-4) and modern bamboos
Arundinaria gigantea (5-6) and Fargesia wuliangshanensis T.P. Yi (7).
1, Amplification of a part of leaf blade, showing the venation pattern and epiphyllous
fungi (indicated by white arrows), Paratype, SZT0001-3, scale bar = 5mm;
2, fine teeth (black arrow) on leaf blade margin, Paratype, SZT0003-3, scale bar =
200μm;
3, macro-hairs (white arrows) on epidermis, prickle-hairs or prickle-hair bases (black
arrow) along the costal zones, Paratype, SZT0001-3, scale bar = 200μm;
4, separated leaf blade epidermis, showing epiphyllous fungi (black arrow), band of
probable bulliform cells (white arrow), Paratype, SZT-S-0001, scale bar = 200μm;
5, macro-hairs (black arrows) on leaf blade epidermis of A. gigantea, Kun No.
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0927028, scale bar = 200μm;
6, fine teeth (black arrow) on leaf blade margin of A. gigantea, Kun No. 0927028,
scale bar = 200μm;
7, adxial leaf blade epidermis of a modern bamboo F. wuliangshanensis, showing
bands of bulliform cells (black arrow) and the third order parallel veins (white arrow),
ALS-S-0001, scale bar = 100μm.
Plate III. Branch leaf blades and culm leaf blades of Bambusium latifolia (1-6) and
modern bamboo Melocalamus arrectus T.P. Yi (7).
1, Branch leaf blade with basal part with pseudopetiole (black arrow), Holotype,
SZT0009b-1, Scale bar = 5 mm;
2, fragmentary basal part of culm leaf blade with short pseudopetiole (black arrow),
Paratype, SZT0010b-8, scale bar = 5 mm;
3, fragmentary basal part of culm leaf blade with short pseudopetiole (black arrow),
Paratype, SZT0010b-15, scale bar = 5 mm;
4, branch leaf blade with middle and basal part, showing broad leaf blade base (black
arrow), Paratype, SZT0009b-2, Scale bar = 5 mm;
5, branch leaf blade with middle and basal part and an incomplete pseudopetiole
(black arrow), Paratype, SZT0010a-1; black triangle indicate a damaged area by
pathogens in another branch leaf blade, Paratype, SZT0010a-10, Scale bar = 5 mm;
6, fragments of fossil leaf blades (Paratype, SZT0010a) including branch leaf blades
(black triangles: SZT0010a-3, SZT0010a-10, SZT0010a-14; white arrow:
SZT0010a-2) and a basal part of culm leaf blade (black arrow: SZT0010a-8), white
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arrow shows the attenuate leaf apex, black triangles indicate damaged areas by
pathogens, scale bar = 10 mm;
7, leaf blade of modern bamboo M. arrectus on lower part of the culm, showing the
short and wide pseudopetiole (black arrow), XTBG-0001, scale bar = 5 mm.
Plate IV. Micromorphology of Bambusium latifolia (1-6) with epiphyllous fungi and
pathogen-damaged areas on the leaf blades and modern bamboo Arundinaria fargesii
E.G. Camus (7).
1, Details of leaf blade venation, white arrows indicate epiphyllous fungi, Paratype,
SZT0009a-7, scale bar = 2 mm;
2, details of leaf blade venation, Paratype, SZT0010a-3, scale bar = 2 mm;
3, prickle-hairs or prickle-hair bases (white arrow) in the intercostal zones, Paratype,
SZT0010a-5, scale bar = 500μm;
4, prickle-hairs or prickle-hair bases (white arrow) along the costal zones, Paratype,
SZT0010a-8, scale bar = 200μm;
5, enlargement of one damaged area by pathogens, Paratype, SZT0011-5, scale bar =
500μm;
6, part of leaf blade showing epiphyllous fungi (white arrow), Paratype, SZT0010a-10,
scale bar = 500μm;
7, part of leaf blade of A. fargesii with damaged area by pathogens (white arrow), Kun
No. 0384198, scale bar = 2mm.
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Plate V. Culms of Bambusiculmus latus (1-4) and Bambusiculmus angustus (5-8).
1, three culms (a, b, c) of B. latus. a, Holotpye, SZT0012a-1; b and c, Paratypes,
SZT0012a-2, SZT0012a-3, scale bar = 5 cm;
2, three culms (a, b, c) that are counterparts of those in “1”. a, Holotpye, SZT0012b-1,
b and c, Paratypes, SZT0012b-2, SZT0012b-3, scale bar = 2 cm;
3, enlarged nodal region of one culm (a) in “1”, showing nodal line (triangle) and the
supranodal ridge (arrow), Holotpye, SZT0012a-1, scale bar = 1 cm;
4, enlarged nodal region of one culm (a) in “2”, showing nodal line (triangle) and the
supranodal ridge (arrow), Holotpye, SZT0012b-1, scale bar = 1 cm;
5, a part of culm of B. angustus with one node (arrow) and two incomplete internodes,
noting the outer (white triangle) and inside (black triangle) surface of the impressed
culm-wall, Holotpye, SZT0013a, scale bar = 2 cm;
6, enlargement of the nodal region, showing the nodal line (triangle) and the
supranodal ridge (arrow), Holotpye, SZT0013a, scale bar = 1 cm;
7, enlarged nodal region of the counterpart of the culm in “6”, showing the nodal line
(triangle) and the supranodal ridge (arrow), Holotpye, SZT0013b, scale bar = 1 cm;
8, enlargement of the nodal region of the culm in “6”, showing the remnant basal
parts of the culm sheath (triangle), Holotpye, SZT0013a, scale bar = 5 mm.
Table captions:
Table 1. Comparison of Sanzhangtian fossil bamboo leaf blades with other fossils.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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PlateI
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Plate II
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Plate III
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Plate IV
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Plate V
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Table 1. Comparison of Sanzhangtian fossil bamboo leaves with other fossils.
Fossil species Leaf
width
(mm)
Lateral
vein
number
Third order
parallel
vein number
Lateral
vein space
(mm)
Third order
parallel vein
space (mm)
Cross vein
space
(mm)
References
Bambusa ilinskiae 55 8-10 6-10 Shvareva, 1970
Sasa kodorica 35 Kolakovsky, 1964
S. lugdunensis 6; 15 3; 5 5 Givulescu, 1984
Phyllostachys sp. 12 Miki, 1941
Bambusium sp. A 30-45 7-10 5-9 Ozaki, 1980
Bambusium sp. B 15-20 5-7 5-7 Ozaki, 1980
Bambusa sp. 6-12 2-4 4-6 Roiron, 1991
“Bambusa”lugdunensis 15-20 5 Martinetto, 2003
“B.”lugdunensis 8-20 4-6 (4) 5-9 (6-7) 1-1.5 0.15-0.2 0.15-0.35 Worobiec and
Worobiec, 2005
Bambusium angustifolia 7-16
(12.7)
3-6 (4) 5-8 (6-7) 0.86-2.23
(1.27)
0.12-0.27
(0.19)
0.35-1.07
(0.61)
present paper
B. latifoliaa 14-38
(21.6)
4-7 (6) 5-9 (7) 1.29-3.07
(1.87)
0.18-0.42
(0.24)
0.26-1.02
(0.57)
present paper
a Branch leaves.
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Highlights
• The earliest bamboo record of China was reported from the middle Miocene of
Yunnan.
• Two genera with four new species were described by leaf blade and culm fossils.
• Bamboo had diversified in Yunnan as early as the middle Miocene.
