全 文 ：古生物学报 , 46(2):183-194(2007 年 6 月)
Acta Palaeontolo gica Sinica , 46(2):183-194(June , 2007)
收稿日期:2006-10-30
＊国家自然科学基金(40232019)、全国博士学位论文作者专项资金资助项目(200429)及教育部博士点基金资助。
湖北长阳上泥盆统一种石松植物＊
薛进庄 郝守刚
(北京大学地球与空间科学学院 , 北京 100871 , sghao@pku.edu.cn)
提要 描述一种采自湖北上泥盆统弗拉阶黄家蹬组中的石松植物。 该植物茎轴纤细。叶基纺锤形 , 螺旋排
列。叶线形 , 叶缘具刺。具顶生的孢子叶球。其孢子叶匙状或披针形 , 边缘具刺。孢子囊呈圆形或椭圆形。植物
茎具原生中柱。原生木质部呈小脊状位于中柱边缘。 后生木质部管胞由梯纹分子组成 , 在加厚棒之间没有类似
“威廉姆逊纹”的连接物。该植物与采自湖南中泥盆统基维特阶的 Longostachy s(Zhu , H u and Feng)Cai and Chen
可比较。它们在茎轴 、线形和具刺的叶 、纺锤形和螺旋排列的叶基 、匙状披针形的孢子叶 ,以及叶 、叶基和孢子叶的
度量等特征方面均非常相似。两者在解剖特征上存有差别 , 即当前植物不具次生木质部 ,不具髓 ,后生木质部加厚
棒之间不具连接物。考虑到现有特征并不足以建立新属种 , 暂归入 cf.Longostachy s sp.
关键词 石松植物 cf.Longostachy s sp. 管胞 弗拉期 湖北 中国
A LYCOPSID PLANT FROM THE UPPER DEVONIANOF CHANGYANG ,
HUBEI PROVINCE , CHINA
XUE Jin-zhuang and HAO Shou-gang
(School o f Earth and Space Sciences , Peking Universi ty , Beij ing 100871, China , sghao@pku.edu.cn)
Abstract A lycopsid plant with preserved morpho logy and anatomy is described from the H uang jiadeng Forma-
tion(Frasnian)o f Hubei Province.Its stems are slender .The leaf bases are spindle in shape , and ar ranged in he li-
ces.Leaves are persistent and spiny.This plant bears distal cones.Sporophyll is spoon-like and lanceolate in form ,
with spines along its m argins.Sporang ia are circular o r elliptical in surface view.In anatomy , the stem has a so lid
strand of exarch primary xylem.Pro toxylem tracheids , composed of annular or helical elements , appear as minute
ridges on the stele periphery.Metaxy lem tracheids are composed of scalariform elements , showing no connecting
“Williamson s striations” between the bars.The shared characte ristics o f the present plant and Longostachys(Zhu ,
Hu and Feng)Cai and Chen , from the upper Middle Devonian(Givetian)of H unan Province , lie in linear and spiny
leaves , spindle-shaped and helically ar ranged leaf bases , spoon-like o r lanceolate sporophy lls;fur ther more , the di-
mensions of leaves , leaf bases and sporophy ll a re also quite alike.However , they show differences in some anatomical
characte ristics;the present plant bears no secondary xylem , no pith , and no connecting materials be tw een thickened
bars o f metaxylem tracheids.The preserved characte ristics , however , are incomple te fo r establishing a new species.
We temporarily assign our specimens to cf.Longostachys sp.
Key words Lycopsida , cf.Longostachys sp., tr acheids , Frasnian , Hubei , China
1 INTRODUCTION
The Mid-Late Devonian period w as an important
interval in the evolutionary his tory of lycopsids.During
this period the herbaceous and arborescent , homospo-
rous and heterospo rous , eligulated and ligulated f orms
coexisted and dominated in certain landscapes.Taxo-
nomically these forms are att ribut ed to the Lycopodia-
les , Prot olepidodendrales and Isoe¨tales sensu lato , or
are considered to be Incer tae sedis (Xue et al .2006).
Among these forms , t he bes t known plant s include
several protolepidodendraleans and others , such as Cy-
clost igma (Chaloner and Boureau , 1967;Chaloner ,
1968), Minarodendron(Li , 1990), Sublepidodendron
(Wang et al ., 2003;Wang and Xu , 2005), Leptoph-
loeum (Cai and Qin , 1986;Li et al., 1986;Geng ,
1990;Wang et al ., 2005), and Longostachys(Cai and
Chen , 1996).The others are f ragmentally preserved.
They are of ten partially preserved as dif ferent modes or
dif ferent organs , making association and comparison
dif ficult.Some are compressions or impressions and
have no anatomical information (e.g., Grierson and
Banks , 1963;Schweit zer and Cai , 1987;Chit aley and
Pigg , 1996), while o thers are permineralized , with
few morphological characters (Mat ten , 1989;Roy and
Mat ten , 1989;Klavins , 2004).Fertile characters of
some genera have been revealed , but those of others
remain unclear.More collections are needed to reveal
the taxonomic and phylogenetic significance of these
fossils.
A large number of lycopsids have been described
from the Mid-Upper Devonian of South China , inclu-
ding Cyclost igma , Chamaedendron , Lepidodendrop-
si s , Lepidostrobus , Leptophloeum , Longostachys ,
Minostrobus , Monilistrobus , Stigmar ia , Sublepi-
dodendron , Wuxia and protolepidodendraleans Colpo-
dexy lon , Hubeiia and Minarodendron (Cai and Qin ,
1986;Li et al ., 1986;Schweit zer and Cai , 1987;Li ,
1990;Cai and Wang , 1995;Cai and Chen , 1996;
Schw eitzer and Li , 1996;Wang , 2001;Wang et al.,
2002;Berry et al ., 2003;Wang and Berry , 2003;
Wang et al., 2003;Xue et al., 2005).These discov-
eries have demonst rated a more complex evolutionary
picture than previously thought and have improved our
understanding of the evolution and diversification of
early ly copsids.Fo r inst ance , Wuxia , f rom the Upper
Devonian of Jiangsu Province , was considered one of
t he earliest Devonian examples bearing bist robilate re-
productive st ructures (Berry et al ., 2003), whereas
the distribution of sporophylls show s specific cone-like
s tructure in Moni listrobus and Wuxia (Berry et al .,
2003;Wang and Berry , 2003).The w orldwide genus
Sublepidodendron was emended and established into a
whole plant species based on specimens from South
China as an earliest representative of isoe¨taleans
(Wang et al., 2003;Wang and Xu , 2005).Some of
t hese species , such as Hubei ia (Xue et al ., 2005),
show t ransitional characteristics intermediat e between
different orders (e.g., Pro tolepidodendrales and
Isoe¨tales), and therefore are of unique significance in
t racing evolutionary trends of certain characters.In
this paper , specimens assignable to cf.Longostachys
sp.are described f rom the Upper Devonian of H ubei
P rovince , China , adding new information to the char-
acter variation of the early lycopsids.
2 MATERIALS AND METHODS
The present plant was collected f rom the
H uangjiadeng Fo rmation , 20 km southwes t of Changy-
ang County , Hubei P rovince , China.The GPS location
is 30°23.12′N and 111°07.89′E.The locality and st ra-
tigraphic details have been described in Xue et al .
(2005).The Huangjiadeng Formation is F rasnian in
age according to the bios tratig raphic dat a(Xian et al .,
1988;Cai and Wang , 1995;Cai , 2000).The speci-
mens were collected f rom tw o beds in the lower part of
t his formation at the same locali ty.The lower bed ,
called bed I here , is about 1 m in thickness , and com-
posed of light gray muds tone.The lycopsid fossils oc-
cur in the middle part of the bed , about 40 cm above it s
lower surface.This bed contains a complex plant as-
semblage , including a probable t rimerophyte bearing
t erminal pairs of sporangia , a primitive fern with well-
preserved vegetative and fertile organs , a probable pro-
gymnosperm plant and the present ly copsid.The other
bed , bed II , is about four meters above bed I and com-
posed of dark gray silty muds tone , with a thickness of
30 cm.Specimens from bed II are remains of a pro-
184 古 生 物 学 报 第 46 卷
gymnosperm and a lycopsid.Based on the examination
of the stems (diameter), leaves (at tachment , dimen-
sions , and spines)and leaf bases (shape and arrange-
ment), we consider that the lycopsid specimens from
bed I (representative of Text-fig.1-a-c)and bed II
(representative of T ext-fig.1-d -j)are conspecific.
The specimens f rom bed I are preserved as impressions
and compressions , while those f rom bed II are only im-
pressions.
Specimens preserved as impressions have been
prepared with st eel needles to enhance thei r exposure
(Leclercq , 1960;Fairon-Demaret et al., 1999).Some
fusainized compressions from bed I were removed from
the rock mat rix and observed with scanning elect ron
microscopy in the Electron Microscopy Labo ratory of
Peking University(SEM ;AMARY 1910FE).One fu-
sainized stem w as prepared by the s tandard procedure
of embedding , sectioning , grinding , and polishing f or
examination using optical microscope (Stein et al.,
1982).Peel and maceration technique failed to obtain
spores.Altogether there are mo re than 30 specimens ,
and five t ransverse and two longitudinal slides.
3 SYSTEMATICPALAEONTOLOGY
Longostachys is the earlies t lycopsid acquiring
both secondary xy lem and heterospo ry features.It w as
originally considered to be the earliest member of t he
Lepidodendrales , and a new family , Longost achyace-
ae , was erected to accommodate it (Cai and Chen ,
1996).In recent cladis tic analysis , Lepidodendrales is
nes ted in Isoe¨tales , and thus L.la tisporophy llus , an
expanded definition of Isoe¨t ales has been sugges ted
(DiMichele and Bateman , 1996).In our opinion , Lon-
gostachy s cannot be readily put into the order Isoe¨tales
sensu lato because it lacks a t rue rhizomorph , which is
the w ell-defined synapormorphy fo r this order.Addi-
tionally , further investigations are still needed to reveal
i ts ligule and details of sporangia(at tachment and ar-
rangement).Our specimens are provisionally identified
as cf.Longostachys sp.
Class Lycopsida
Order Incertae sedis
Genus Longostachys (Zhu , Hu and Feng)Cai and Chen
Type species Longostachys latisporophy llus
(Zhu , Hu and Feng)Cai and Chen
cf.Longostachys sp.
(Text-figs.1—5)
Repository Department of Geology , School of
Earth and Space Sciences , Peking University , Beijing ,
China.
Diagnosis Slender lycopsid.Stems dichot omously
branched , averaging 4 mm in diameter.Leaves linear ,
relatively long , with a maximum length up to 25 mm ,
departing f rom the stem at an angle of 45°—90°.Leaf
bases spindle-shaped , arranged in helices , forming
s teep parastichies with six to eight per gyre but lacking
ho rizontal row s.Length ca.5 mm , and the wides t
portion ca.0.8 mm at about middle part.Sporophyll
spoon-like and lanceolate in shape , and ca.2 cm in
length , consis ting of a pedicel and a lanceolate lamina.
Spines attached to margins of sporophyll , with a length
ranging from 1mm to 3.5mm.The widest portion of
t he lamina ca.4mm.Associated cones terminally atta-
ched.Sporangia might be spherical or ellipsoid , ca.
2.0mm wide and 1.7mm high.Spores unknow n.Stem
having a solid strand of primary xy lem measuring ca.
0.7—1.5mm in diameter.Primary xylem exarch.P ro-
toxylem t racheids appear as minute ridges on the st rand
surf ace in t ransverse section , and composed of annular
and helical elements.Each protoxylem point consisting
of 5—10 cells.Metaxylem t racheids comprising scalar-
iform elements , and lacking connecting material be-
tw een thickened bars.
Locality South s lope of Mt.Luoyan , ca.20 km
southwest of Changyang County , Hubei P rovince ,
China.The GPS location is 30°23.12′N and 111°07.
89′E.
Horizon Huangjiadeng Formation , Upper Devo-
nian (F rasnian).
4 DESCRIPTION
4.1 Stems , leaf bases and leaves
The dimensions and g ross morphologies of the
s tems and leaves from both beds are well within the
range of variation of a single species (compare Text-
fig.1-a—c with Text-fig.1-d—j).The preserved
185 第 2 期 薛进庄等:湖北长阳上泥盆统一种石松植物
stems range f rom 2 to 6 mm in width , with an average
value about 4 mm , exclusive of leaves (Tex t-fig.1-a ,
c , d).The longest s tem is ca.60 mm , and the two
ends were broken.Some s tems are isotomously
branched at an angle of about 45°(Text-fig.1-e).
The surfaces of the s tems are generally coalified so
that leaf bases are deformed , except for two examples.
The leaf bases appear to be arranged in helices , form-
ing s teep parastichies with six to eight per gy re but lac-
king horizontal rows (Tex t-figs.1-f , g , 2-a).They
are spindle-shaped.Their length is ca.5 mm , and the
widest portion is ca.0.8 mm at about the middle part.
They merge with those of the second gy re above and
below.
Text-f ig.1 T he ex ternal morphology of cf.Longostachy s sp.
a—c.Specimens col lected from bed I.d— j.Specimens from bed II.a.Holo type.A permineralized s tem.A rrow points to the leaf enlarged in
b.Specimen:PKU-XH-55.Scale bar=5mm.b.Enlargement of a leaf at tached to the s tem in a , show ing i ts mino r spines(arrow s).Scale bar
=2mm.c.A stem w ith leaves along its m argin s.Specimen:PKU-XH-59.Scale bar=3mm.d.An impression stem , show ing ident ical charac-
terist ics to the stem s in a and c.Specimen:PKU-XH-60.Scale bar=5mm.e.A dichotomous stem.Specimen:PKU-XH-61.Scale bar=5mm.
f.A stem showing leaves and leaf bases.Specimen:PKU-XH-63.Scale bar=5mm.g.Enlarged part of f(low er part), showing the fo rm and
ar rangemen t of the leaf bases.A rrow s point to expanded proximal parts of the leaves.Scale bar =3 mm.h.A stem apex w ith tigh t clu sters
of leaves.Specimen:PKU-XH-64.Scale bar=10mm.i.A stem with leaves at tached.Specimen:PK U-XH-65.Scale bar=4 mm.j.Enlarged
part of i(upper part), showing spines along leaf m argin s(arrow s).Scale bar=3mm.
Numerous persis tent leaves are attached to s tems
and stem apices (Text-fig.1-h , i).They depart from
the stem at an angle of 45°-90°.Leaves are linear and
relatively long , with a maximum length of up to 25 mm
(Text-fig.1-a , d , h).Complete leaves are rarely pre-
served , and their delicate dist al tips are alw ays broken.
The very proximal part s of the leaves are apparent ly
decurrent (Text-fig s.1-g , 2-a).The leaf width is ca.
0.3 mm , and this width is stable along most of t he
length .Spines are irregularly dis tributed along leaf
margins , with various shapes and dimensions (Text-
figs.1-b , j , 2-b).The length of the spines ranges
from 0.2 to 1.5mm.
4.2 Reproductive structures
Two partially preserved terminal cones (Text-fig.
3-a), and one isolated sporophyll(Text-fig.3-b)have
been recovered in our collections.The isolated sporo-
phy ll w as found in bed I.The present plant is the only
lycopsid found in this bed.The sporophyll is spoon-like
and lanceolate in shape , and ca.2 cm in length , but its
delicate tip is broken (Text-fig.3-b).It demons trates
a pedicel about 3 mm long and 1mm wide , and then i t
abrupt ly expands to form a lanceolate lamina.Many
spines are att ached t o the margins of the sporophyll ,
with a length ranging f rom 1 to 3.5mm.The wides t
portion of t he lamina is ca.4mm exclusive of spines.
Concerning the tw o separately preserved cones , we
suggest that they belong t o the present plant because
they occur with the vegetative stems in the same sedi
mentary plane(Text-fig.3-a)and have the spines a-
long leaf/ sporophy ll margins.The longer cone (Text-
fig.3-c , right)is 7mm in length and 4mm in width ,
and the other is 4.5mm long and 3mm wide.Their
spo rophylls are also spiny (Text-fig.3-c , arrow s).
The observed sporangia are arranged in two vertical
rows as impression(Text-fig.3-c , left).The sporang-
ia measure ca.2.0mm wide and 1.7mm high , but it is
difficult to determine thei r shape in three dimensions;
t hey may be spherical or ellipsoid.A few possible iso-
lat ed sporangia are preserved near vegetative stems ,
and show the same shape and dimensions (Text-fig.3-
a , arrow).Both of the cones obviously are only the
t opmost f ragments of the enti re s tructure , and thus the
measurements probably represent their immature
s tate.The attachment detail of the sporangia remains
unclear.Peel and maceration techniques failed to obt ain
in situ spores.
4.3 Anatomy
In t ransverse section , the axes are circular or
somew hat ellip tical in outline and 3.5 mm in diameter
(Text-fig.4-a).Solid primary xylem st rands occupy
the center of axes.The strands are circular or ellip tical
in t ransverse view , and the diameter is ca.0.7—1.5
mm(Text-fig.4-a , b , 5-a).Some coalified materials
occupy the cent er of the st rands in some sections
(Text-fig .4-b);obviously this is a result of filling in
186 古 生 物 学 报 第 46 卷
187 第 2 期 薛进庄等:湖北长阳上泥盆统一种石松植物
Text-f ig.4 Anatomy of cf.Longostachys sp., seen by light micros cope
a.T ransverse section of a permineralized stem.Slide:PKU-XH-50-2.Scale bar=500μm.b.Enlargem en t of the s tele of the stem shown in a ,
but of another slide.Arrow points to the part enlarged in c.Slide:PKU-XH-50-1.Scale bar=200μm.c.Enlarged part of b , show ing cortex
tissues , presumed phloem cavi ty , protoxy lem points and metaxy lem tracheids from top to bot tom.Scale bar=50μm.d.Longi tudinal sect ion of
metaxylem tracheids.Slide:PKU-XH-51-1.Scale bar=60μm.e.Enlargement of metaxy lem tracheid s in tran sverse section.Slide:PKU-XH-
50-3.Scale bar=20μm.f.Enlarged part of d.Scale bar=20μm.g.Longitudinal sect ion show ing p rotoxylem tracheid s w ith annu lar(arrow s)
and dense helical thickening s , and metaxylem tracheids w ith scalari form bars from lef t to right.S lide:PK U-XH-51-1.Scale bar=50μm.
Tex t-fi g.2 Line d raw ings of the stems of cf.Longostach ys sp.
a.Leaf bases , with a spindle shape and a helical arrangement pat tern.Specimen:PKU-XH-63(T ext-fig.1-g).b.Spines along leaf
margins show ing various shapes and dimension s.Specimen:PKU-XH-65(T ex t-fig.1-i).Scale bar=3mm.
Tex t-fi g.3 Reproduction s t ru cture of cf.Longostach ys sp.
a.A sterile stem and tw o cone apices(lef t part)in the same sedimen tary plane.Arrow points to a possib le isolated sporangium.Spec-
imen:PK U-XH-67a.Scale bar=5mm.b.An isolated sporophyl l in bed I , showing a spoon-like and lanceolate shape.Scale bar=
4mm.c.Enlargement of the two cone apices , show ing sporophyl ls wi th spines(arrow s), and circular sporangia.Scale bar=2mm.
188 古 生 物 学 报 第 46 卷
189 第 2 期 薛进庄等:湖北长阳上泥盆统一种石松植物
the cellslacuna rather than an indicative of a parenchy-
matous pit h.
P rotoxylem t racheids appear as minut e ridges in
t ransverse section , si tuated at the periphery of t he xy-
lem st rand(Text-fig.4-c).Larger metaxy lem t rache-
ids develop centripetally f rom protoxylem points.The
primary xylem is thus exarch.It is difficult to count
the exact number of the protoxylem points.Each pro-
toxylem point is generally made up of about 5—10 cells
(Tex t-fig.4-c).In transverse section , protoxylem t ra-
cheids are circular to elliptical in outline , and range
from 4μm to 10μm in diameter.View ed in longitudinal
section , the prot oxylem is composed of annular and
helical element s (Text-fig s.4-g , 5-d).The thickened
bars of the protoxylem tracheids adjacent to the meta-
xy lem are twice as dense as those of t he outmos t t ra-
cheids (Text-fig.5-d).The number of bars varies
from three to six per 20μm.
In transverse section , metaxylem tracheids are po-
lygonal and show g reat variation in dimensions , avera-
ging 26.5 μm radially and 22.1 μm tangentially (Text-
figs.4-c , e , 5-b , c).The metaxylem is composed of
scalarifo rm element s(Tex t-figs.4-d , g , 5-e);no oth-
er element s were observed.The length of the pit s va-
ries from 6μm to 20μm , and the height averages 4μm.
There is no connecting material between two adjacent
thickened bars (Text-figs.4-f , 5-e).The height of the
bars is 4.9 μm(Tex t-fig.4-g;N =18)and the densi-
ty , 13—15 bars per 100 μm (Text-fig.4-g).
Cellular details of phloem and cortex tis sues are
poo rly preserved (Text-fig.4-a).In transverse sec-
tion , several layers of cells can be observed just outside
the s trand (Text-fig.4-c , arrow), w hich , considering
thei r location and appearance , probably represent cor-
tex tissues.The cells are most ly filled by coalified ma-
terial and are ca.13.3μm radially by 19.2μm tangen-
tially in dimensions.
5 DISCUSSION
5.1 Comparison to Longos tachys
Morphologically , our present plant show s great
similarities t o Longostachys lati sporophy l lus.Lon-
gostachy s has been described f rom the upper Middle
Devonian of Hunan Province , China (Cai and Chen ,
1996).We also compare our specimens with those of
Longostachys collected f rom the type locality(collected
by one of the workers).Longostachys bears a rhizome ,
which branches dichot omously t o form a three-dimen-
sional funnel-like roo ting system.It s stems range f rom
35mm to 2mm in width f rom the trunk bases to distal
branchlet s.The preserved stems of our plant are 2—
6mm in width.Longostachys bears persis tent , linear
and simple leaves.The leaves of Longostachys are
2.0—7.0 cm in length and 0.6—1.0 mm in width ,
while the leaves of t he present plant are up to 2.5cm
long and 0.3mm wide , t hinner than the former.The
leaves of Longostachy s and our plant bear spines of a-
bout 1mm long along their margins.The shape and size
of t he leaf bases , and the number in each gy re of the
t runk or branch is highly variable in Longostachy s.It s
leaf bases are 1—1.5mm wide , 2—10mm long , and
6—16 per gy re.Near the t runk base , the leaf bases are
oval t o fusifo rm , w hile in the upper portion of the
t runk and the branches , t hey become narrow and long ,
and spindle-shaped in f orm.As to our plant , only spin-
dle-shaped leaf bases were preserved , with dimensions
of 0.8mm wide , 5mm long , and 6—8per gyre , and
they are comparable t o the spindle-shaped leaf bases in
Longostachys.The leaf bases of both plant s are ar-
ranged in helices.The spo rophylls of the present plant
is spoon-like and lanceolat e , about 2cm long , with
spines 1—3.5 mm long.The sporophylls of Lon-
gostachys are also spoon-like and lanceolate , 1.5—3cm
long , and have spines 1—1.6mm long.The cones of
Longostachys are very long , and can reach a length of
22.5cm , but the preserved cones of our plant are obvi-
ously only apex part s(about 7 mm in length), making
the comparison dif ficult.To sum up , our present plant
shares some characteristics with Longostachys.The
dif ferences lie in the measured dimensions of the leav-
es , leaf bases and s tems (Table I).Additionally , the
present plant lacks any evidence of root organs.Con-
sidering the preserved condition of our present plant ,
the lack of a rhizome and larger trunks comparable to
those of Longostachys is probably a taphonomic bias re-
sulting f rom transpo rt ation of the specimens before fi-
nal burial.
Comparison of the anat omy of Longostachys and
our specimens is complicated by the great variation re-
190 古 生 物 学 报 第 46 卷
Tex t-fi g.5 Anatomy of cf.Longostachys sp., examined wi th s can ning elect ron microscopy(SEM)
a.T ransverse view of the stele.Scale bar=200μm.b.Enlarged part of a stele , showing metaxylem tracheids and scalari form ly thick-
ened bars in oblique view.Scale bar=30μm.c.Enlargement of metaxylem tracheids.Scale bar=20μm.d.Longitudinal view of pro-
toxylem and mataxy lem tracheids , show ing annu larly and scalariformly thickened bars.The thickened bars of the protoxylem trache-
id s adjacen t to the metaxylem(near middle)are tw ice as dense as those of the outermo st t racheids(left).Scale bar=20μm.e.Longi-
tudinal view of metaxylem tracheid s.Note the lack of any connect ing material betw een adjacent thickened bars.Scale bar=20μm.
sulting f rom the ont ogeny of different tissues.Lon-
gostachy s bears a solid prot os tele wi th secondary xylem
in the rhizome and t runk base , and a stele with mixed
pi th and with li ttle or no secondary xylem in the upper
part of the t runk and the distal branches.Our plant has
a solid primary xylem st rand lacking pit h and secondary
xylem.The protoxylem of both plants is similar in ap-
pearance , and forms minute ridges on the periphery of
the primary xylem st rand in t ransverse section (e.g.,
Cai and Chen , 1996 , plate 19 , Text-fig.2;this paper ,
Text-fig.4-c).Longostachys has secondary xy lem but
our plant lacks.In the permineralized dist al branches
of Longostachys , t he steles are all medullated , even in
a very small st robilus axis;this st robilus axis is of
1.6—1.7mm in diameter , and the stele measures ca.
0.5mm (Cai and Chen , 1996 , plate 19 , Text-fig.1).
We suspect that a protos tele with mixed pit h is a basic
stelar configuration of Longostachys , and w ould persis t
in even smaller axes.As to our plant , the sectioned ax-
es are 3.5mm in diameter , and bear solid prot osteles of
ca.0.7—1.5mm.According to the ontogenetic model
of arbo rescent ly copsids , however , solid protost ele and
191 第 2 期 薛进庄等:湖北长阳上泥盆统一种石松植物
表Ⅰ Comparison of the present plant with Longostachys
Stem Leaves Leaf bases Spo rophylls Cone
Present stem s 2—6mm
Linear and spiny , up
to 2.5cm in length ,
0.3mm w ide , spines
0.2—1.5mm long
Spindle-shaped , heli-
cally arranged , 0.8mm
wide , 5mm long , 6—
8per gyre
Spoon-like and lanceolate , w i-
dest port ion 4mm , w ith
spines of 1—3.5mm long
7mm long and 4mm
wide , sporangia spheri-
cal or el lipsoid(in apex
part)
Longostachys
lat isporophyl lu s
10—35mm
Linear and spiny , 2—
7cm in leng th , 0.6—
1.0mm w ide , spines
about 1mm long
Spindle-shaped , helically
arranged , 1—1.5mm
wide , 2—10mm long ,
4— 6per gy re
Spoon-lik e and lanceolate ,
1.5—3cm long , w idest por-
t ion 4.6mm , w ith spines of
1.0—1.6mm long
3—22.5cm long , 0.7—
1.0cm wide , megaspo-
rangia roundish to ellip-
tical
protostele with mixed pith can occur in a single species ,
and the size of these two types of protost ele can overlap
at least sometimes (Eggert , 1961).As a consequence ,
the difference of protostele fo rm in distinguishing be-
tween Longostachy s and our plant remains only specu-
lative.The t racheids of metaxylem and secondary xy-
lem of Longostachy s bear pit-like opening s or “William-
son s s triations” between thickened bars (Cai and
Chen , 1996 , plate 16 , Tex t-fig.7 , plate 18 , Tex t-fig.
7);here , we call this structure connecting material.
Our present plant obviously lacks this st ructure as ex-
amined by LM and SEM .
5.2 Comparison to other related plants
Fossils of such taxa as Chamaedendron , Wuxia
and Moni listrobus f rom Middle-Upper Devonian of
South China also show resemblances to our specimens.
Chamaedendron was described f rom the Late Devonian
of Hubei P rovince (Schw eitzer and Li , 1996).Wuxia
and Moni listrobus are f rom the Late Devonian of Jiang-
su Province (Berry et al ., 2003;Wang and Berry ,
2003).They all have slender stems and spiny leaves.
Their sporophylls are also spoon-like and spiny at the
margins.As in our specimens , the metaxy lem t rache-
ids of Chamaedendron are mainly composed of scalari-
f orm element s , and lack connecting material between
thickened bars.Chamaedendron diff ers from our pres-
ent stems in its w horled arrangement of leaf bases.
Wuxia has connecting material betw een thickened
bars , and Moni listrobus bears neck-like fertile st ruc-
tures , but lacks information about their int ernal anato-
my information (Berry et al., 2003;Wang and Berry ,
2003).
Our plant differs f rom herbaceous protolepidoden-
draleans in the morphology of its leaves , and leaf ba-
ses , and in the presence of dis tal cones.Sporophylls of
protolepidodendraleans are undifferentiated and do no t
aggregate into compact cones.Metaxylem tracheids of
our plant are composed of scalarifo rm element s , w hich
is comparable to Minarodendron and Hubeiia (two
genera of P rotolepidodendraceae)found in South China
(Li , 1990;Xue et al., 2005).However , the latter
two plant s possess connecting material (i.e., fimbrils
or multiperforat ed pitlet sheets) between thickened
bars , an important difference.
Atasudendron mirum , from the Middle Devonian
of Kazakhstan (Iurina and Lemoigne , 1975;Sen-
kevit sch et al ., 1993), differs f rom our specimens in
leaf base morphology.Leaf bases of Atasudendron are
elongated-rhomoboidal and rhomboidal in shape.Ata-
sudendron also lacks connecting material between
thickened bars.Pet rified lycopsids from Montagne
Noire of France and New A lbany Shale of Kenturky
and Indiana , USA (Meyer-Berthaud , 1984;Roy and
Mat ten , 1989), such as Linietta , Fodiodendron , Tra-
bicaulis and Landey rodendron , all lack morphological
dat a.Concerning anatomical characters , t hey all show
significant dif ferences when compared with our speci-
mens:L inietta , T rabicaulis and Landeyrodendron
possess slight ly developed secondary tissues;Trabi-
cauli s and Landey rodendron possess “Williamsons st ri-
ations” between thickened bars.
Based on the above comparisons , the present plant
is unique in some certain charact eristics , and show s
dif ferences f rom other genera.These differences , how-
ever , prevent us establishing a new species.We tem-
po rarily assign our specimens to cf .Longostachys sp.
based on the apparent similarities compared with the
type species of Longostachys , especially in their outer
mo rphologies.The present plant may represent distal
part s of Longostachy s , and if this is t rue , t he differ-
ences between thei r anat omies can be considered a re-
sult of ontogeny.Alt ernatively , these specimens may
represent a new plant but closely relating to Lon-
192 古 生 物 学 报 第 46 卷
g ostachys.Final establishment of the taxonomy mus t
await f urther collections.
5.3 Tracheid structure of early lycopsids
Among the known early fossil lycopsids , only a
few , such as Chamaedendron and Atasudendron , lack
connecting material (Senkevi tsch et al ., 1993;
Schw eitzer and Li , 1996).Our plant is another exam-
ple in which this st ructure is absent.The absence of
connecting material might be result ed f rom phylogenet-
ic losses , ecological conditions , o r ontogenic levels.
Presently , we cannot exclude any of t hese possibili ties.
The majo rities of early fossil lycopsids possess connect-
ing material;t hese include Barsostrobus , Eskdalia ,
Hubei ia , Landeyrodendron , Leptophloeum , Lon-
gostachys , Minarodendron , Minostrobus , Selaginel-
li tes , Sublepidodendron , Trabicaulis , Wex fordia ,
Wuxia and Carboniferous isoo¨taleans (Xue et al .,
2005 and references therein).In the previous litera-
tures , connecting material between thickened bars has
been termed fimbrils , “Williamson s st riations” , fi-
brils , fibrillar threads , pit let sheet s , or multipleperfo-
rate pitlet sheets , etc.(Klavins , 2004), and show s
dif ferent pat terns f rom those with a sheet of mat erial
in terrupt ed by a number of apertures to those with dis-
tinct longitudinal fibrils (Berry et al., 2003).Taxo-
nomically these genera belong to the Protolepidoden-
drales , Selaginellales and Isoe¨t ales.DiMichele and
Bat eman (1996)considered the presence of fimbrils
(connecting material)t o be the key character t o delimi t
the class Lycopsida in their st rict phy logenetic classifi-
cation.Kenrick and Crane(1997)claimed that the con-
necting material betw een thickened bars of metaxylem
t racheids is homologous with and derived f rom the thin
connecting microporate layer between the helical t hick-
enings of G-type tracheids of drepanophycaleans.How-
ever , t he current evidence can t determine about how
these various pat terns of connecting material correlate
to certain groups within Ly copsida f rom a phylogenetic
view .It seems that t here are some apparent evolution-
ary sequences.For instance , Hubeiia , a member of
Pro tolepidodendrales , bears “Williamsons striations”
as isoe¨ taleans , and thus demonst rates a close relation-
ship between Protolepidodendrales and Isoe¨tales.The
connecting materials of Barsostrobus , Eskdalia ,
Minarodendron and Selaginel lites are apparent ly simi-
lar , which might indicate their evolutionary relation-
ships.Further inves tigations are needed to clarify t hese
is sues.
Acknowledgments We thank the help of Professor
Richard C.Fox , University of A lberta , for carefully
modifying the English text.Dr.Wang Deming , Peking
University , and Dr.Wang Q i , Beijing Instit ute of Bot-
any , are thanked for their helpful advice.The review-
er , Prof.Cai Chongyang of Nanjing Ins titute of Geolo-
gy and Palaeont ology , is thanked for his critical com-
ments.The authors also thank Ni Debao , Jia Qiuyue ,
and Geng Jinda , Peking University , for their help in
preparation of slides and photographs.
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