metric~ ~rtile axes, the other zos~rophylls bring age of these layers, based on the dispe~ed spore then considered ph~ogenefic deadends, assemblage, is early ...
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PALYNoLoPA GyLAEOBoTAR NyEVI WAIDE~o
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Lower Devonian plant remains from Marchin (no hern margin of Dinant Synclinorium, Bdgium). IV. Odonax borealis gen. et sp. nov. Phil~pe G~fienne ~FX~
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~ Likge, P ~ e ~ Vin~ A o ~ L ~
Received 23 December 1994; ~ f i ~ d and accep~d 17 F ~ m a ~ 1995
Ab~ract
A new zosterophyll genus ~ described from the Lower Devonian (early Em~an) of Marchin (Bdgium). The spedmens are poorly preserved and c o n ~ of spin~ mostly ~otomous axes, with a spiny branch in a subaxillary position at some proximal branching points. Spines are triangular in outline. The axes end in compact strobili of sporangia. Because of the exi~ence of two dichotomies ju~ bdow them, the ~robih are often borne in groups of four. The strobili are composed of two rows of sporangi~ arranged in an opposite to akernate manner. The two rows are borne at 100-150 ° apart on the same ~de of the ~robflus axis: the strobili thus show a bilateral rather than radial symmetry. Often, the tip of each s~obilus ~ slightly curved. The reniform sporangia are borne erect by a strong spiny stalk bent upwards di~ally. Dehiscence occurs ~ong thek di~al margin and opens the sporangia into two equal valves, the abaxial one bong spiny. Nothing ~ known about the anatomy and the spores of the plant. This plant has typical zosterophyll characters, and ~s das~ficafion w~thin a new genus rather than in a new speoes of Rebuch~, Sawdon~ or Zosterophyllum ~ discu~ed. The di~incfions between (1) radi~ versus bilateral symmetry in strobili, and (2) terminate and nonterminate axes in zosterophylls are recon~dered.
1. ln~oducfion Since Penhallow (1892) described the fir~ zoOerophyll, Zosterophyllum myretonianum ffevised by Edwards, 1975), m a n y plants with more or ~ c o m p a r a b ~ m o r p h o l o g y have been discovered. A subdivi~on (Zosterophyllophyfina Banks, 1968) was created for them, which recdved a wide acceptance and is now accurately defined (Banks, 1975, 1992; G e n s d and Andrews, 1984; Gensd, 1992; Hueber, 1992). This subdivi~on ~ sometimes devated to the rank of divi~on ~ee, for exampl~ Taylor and Taylor, 1993). Notwithstanding the 003~666~9~$15~0 © 1996 ~ SSDI 0034-6667(95)00121-2
S~en~ B.V. A~ fig~s ~ e d
numerous additions of genera to that subdivi~on and our subsequent increased under~anding of ~, the concept of the zo~erophylls has not changed much ~nce 1968. The taxon includes plants with later~ s p o r a n g i a globose to reniform in shape, and possessing a dehiscence mechanism ~ o n g the di~al margin. T h d r axes branch ~ o t o m o u ~ y to anisotomously. T h d r xylem strand is elliptical in ~ansverse section and iS maturation is exarch (Bank~ 1992; Taylor and Taylor, 1993). There is a gener~ consensus to con~der the zosterophylls closely r d a t e d to the lycopods ~ee, among others, Kenrick and C r a n ~ 1991; Gensd, 1992; Hueber,
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1992). Niklas and Banks (1990) sugge~ed that lycopods arose ~om an early zos~rophylMike group chara~erised by nonterminate, radially symmetric~ ~rtile axes, the other zos~rophylls bring then considered ph~ogenefic deadends, The subdivi~on Zosterophyllophytina is represen~d in B ~ u m by: --Anisophyton c£ go~an# Remy et ~., 1986 (vegetafive spedmens; Gerfienne, 1990a, 1991a); --Ens~alia deb~ndii Gerfienne, 1996; --Forges~ curvata Gerrienne, 1991b; --Gossling~ breconens& (Heard) Heard, 1927 (S~emans and Gerrienne, 1984; Gerrienne, 1990a, b); --Rebuch& (?) pendu& Stockmans, 1940 (Rebuch&=D&tichophyton M~gdeffau according to Schweitzer, 1979); --cf. Sawdon& ornata (Dawson) Hueber, 1 9 7 1 (vegetatNe spe~men~ Gerrienn~ 1983, 1993); --Zos~rophyllum deciduum Gerrienne, 1988; --Z. fertile Leclercq, 1942; - - Z . c£ fertile Le~ercq sensu Edwards (1969) (Gerrienne, 1983). The new B ~ a n zo~erophyll described here was found in the Early Em~an Les Forges locafit~ at Marchin ( B ~ u m ) . This locality has ~ready ~elded an abundant flora (Gerrienne, 1983, 1988, 1990a, 1991b, 1995, 1996) and is still under investigation. The new taxon has pre~ou~y been desc~bed (Gerrienn~ 1990a, pp. 115-125), but is still in need of a valid publication. Moreover, a fu~her spe~men has ~nce been found, which has allowed a better understanding of the arrangement of the sporan~a. The new plant has spiny dichotomous axes and compa~ bilater~ strobili of sporan~a. Most of the specimens are very badly preserved, but detailed information on the morphology of the ~robifi was obt~ned from different aspec~ of impres~ons-compres~ons of this plant.
2. Ge~o~c~ and s~afigrap~c~ setting The Marc~n locality is a ~ s u ~ d quarry called "Les Forg~" (Gerrienne, 1983, fig. 1, point A), ~ the Hoyoux valley, on the northern mar~n of the D ~ a n t Synclinorium (Bd~um). The f o ~ r o u s strata belong to the "Formation de Wtpion"
(Godeff~d et ~., 1994) and are fitho~ratig r a p h i c ~ early Em~an in age. The fossil-bearing hyers are a bdge to green~h shay sandstone. The age of these layers, based on the dispe~ed spore assemblage, is early Emshn [Oppd Zone AB in Stre~ et ~. (1987) and in Steemans (1989~, because of the presence of Emphanisporites annulatus McGregor and Brocho~ile~s bellatu~s Steemans.
3. Methods The plant was ~udied using standard p~aeobotanic~ ~chniques, m~nly dtgagement (Le~ercq, 1960) and ~ a n s ~ (Banks et ~., 1972). The ~ a n s ~ were all unsuccessful: the specimens are preserved only as impressions or as compre~ions with very little carbon ~ . Spe~mens were photographed u~ng a photo~oupe Te~ovar Z~ss with a polafised fight source. Con~a~ b~ween plant and matrix was enhanced by wetting the spe~men with water plus ~cohol (norvanol) and pla~ng a cove~slip on it (this prevents too quick evaporafion of the fiquid). To understand the morph~ogy of the s~obili, plasfi~ne modds were built, compressed in various ways, photographed and drawn (Figs. 3 and 4). Type and figured spe~mens are deposked in the collections of the P~aeobotany Depa~ment of the Uni~e~ity of Litge.
4.
Sy~emafic palaeobotany
Subdi~on ZOSTEROPHYLLOPHYTINA Banks, 1968 Class ZOSXEROPHYLLOPSIDAB~rhor~, 1971 Order ZOST~ROPHYLLALESBanks, 1968 Family ZOSTEROPHYLLAC~AEsensu Hueber, 1972a ODONAX G~fienne, gen. nov. (Plat~ I-III; Figs. 1-5) Type: Odonax boreal# Gemenn~ sp. nov. Diagnosis:Plant with s p r y ~ e ~ aeri~ a ~ sys~m showing mostly ~otomous branc~ng; spiny subax~ary branch present at some p r o ~ m ~ Nfurc-
P. Gerrienne/Reviewof Palaeobotanyand Palynology93 (1996) 89-106 ations; spines randomly ~sttibuted around the axes; axes en~ng ~ compa~ s ~ o b ~ (one s~obflus has been found ~ a s u b t e r m ~ position), often slightly curved, showing often an ~otomy just beneath the strobili or wit~n thek ~ w ~ t par~ strobflus compo~d of two rows of opposite to ~mrn~e s p o r a n ~ ~ro~lus showing bflamr~ symm~ry, the two rows of ~po~an~a bong ~aced on one ~de of the s~obflus a~s. Sporan~a re~form ~ face ~ew, oflen foxed in two, borne on a s~ong s p r y s ~ ~ e d at various acute an~es on the a~s of the s~obflus; st~k bent upwards • ~all~ and beating the sporan~a erec~ de~scence of the sporangium occurring ~ong ~s • ~ m a r ~ ope~ng the sporangium ~ t o two equ~ v ~ v ~ ; a b a ~ v~ve of the sporan~um beating s ~ n ~ . A n ~ o m y and spores unknown. E~mo~gy: G ~ e ~ odou& odonw~ tooth; axon, a~s.
Odonax borealis Gertienne, sp. nov. ( P I ~ Figs. 1-5)
I-IH;
Ho~type: Part, speomen ULg M 13361 P (Pl~e I, 3); coun~rpart a, specimen ULg M 13361 CPa (Plate I, 4, 6); counterpart b, spedmen ULg M 13361 CPb (Pl~e I, 7). Reposimry: P~aeobotany department of the UnNers~y of Liege, B ~ u m . Type ~ c a ~ : "Les Forges" quarry at M a ~ n (Bel~um). A p p r o ~ m ~ d y 6 km south of Huy, northern mar~n of the D ~ a n t Synclinotium. Loca~ty A of G~rienne (1983). Stratigraphic hot,on: Formation de Wtpion (~wer Em~an ~ Godeff~d et ~., 1994); P a ~ n ~ o ~ c ~ Zone AB ~ a d y Em~an ~ Steemans, 1989). E~mo~gy: Latin, boredis, no~her~ from the no~h, because of the geograp~cal position ( ~ the northern part of the D ~ a n t Synclinofium) of the type locality, Diagnosis: Characters as described for the genus, Axes 1.1-2.7mm wide (2=2.06mm; n=30), showing 5-40 ° isotomi~ every 15-30 mm. Subaxillary branch 2.5mm ~ng and 0.5 mm wide; s~nes triangular ~ outl~e, 0.2-0. 5 mm long (g = 0.34 mm; n = 30), 0.4-1.0 mm wide (2 = 0.65 mm; n = 30) at thor base; ~ r o ~ of sporan~a at ~ast
91
3 5 m m ~ n ~ 3 - 5 m m w i d e , the two rows of sporan~ a bong ~aced at 100-150 ° on one ~de of the stem. Sporan~a 2.0-3.7 mm ~gh ( 2 = Z 6 2 mm; n=30) and probably 1.5-4.0 mm wide (they are foxed and thor measu~d width ranges ~om 0.6 to 3.0mm (2=1.71 mm; n=30). St~ks ~ e d on the a~s with an an~e of 45-80 °, bent 90-135 ° upwards; st~ks ~5-1.0 mm wide ~ their base.
D~tion Stem morpho~gy: M o ~ |ban 30 ~rtile specimens have been found, but o ~ y those w~ch add to the under~an~ng of the ~ant a ~ f l ~ r a ~ d . The specimens are all poorly pr~erved; thor usu~ aspect ~ that shown on Pl~e HI, 1. The ~nge~ spedmen ~ 83 mm ~ng and ~ ~ c o m ~ e ~ the base and proba~y at the top (Pla~ I, 3). The ~ant c o n s ~ of mostly isotomously branched ax~ (Plate I, 1-5; Plate lI, 1; PI~eHI, 1), en~ng ~ ~o~ of sporan~a. The an~e of the~ hotomi~ ~ quite acute (5-40°); and the ~ a n t does not branch much: two succes~ve isotomi~ are separ~ed by 15-30 mm. The axes are 1.1-2.7 mm wide (2 = 2.06 mm; n = 30) and cove~d with numerous triang~ar em~gences. A spiny u n ~ d e d subaxillary pr~ection, a p p r o ~ m ~ d y 0.5 mm wide and 2.5 mm ~ng, has been found on two specimens (Pl~e I, 3, 7; Pl~e I, 4; Fig. 1~ b). In spedmen ULg M 13361 P, t~s sho~ a~s is ~aced at the axil of an a~sotomous branc~ng and ~ downwarty ~ed (Pl~e L 3, 7; Fig. 1~. The position and the shape of the suba~Hary branch of the speomen ULg M 13361 CPa (Pl~e I, 4) ~ ~ss dear: R ~ proba~y ~so ~aced at a branc~ng p~nt but is upwar~y ~ e d (Fig. lb). The spines are triang~ar ~ outline (Pl~e HI, 6, 8), somefim~ gently curved Other towards the base (Pl~e III, 9) or the top (Pl~e III, 7) of the ~ant. As ~ r as I know, each tip ~ acumina~ and unforked. They w e ~ present on the entire surface the axes ~ s s u g g ~ d by the irregular surface of these lat~O, on the s p o r a n ~ st~k (Pl~e H, 4-5), and on the a b a ~ v~ve of the sporangia (Plate II, 8) ~ee b~ow). They a ~ 0.2-0.5 mm ~ng ( 2 = ~ 3 4 m m ; n = 3 0 ) and 0.4-1.0mm wide (~= 0.65 mm; n = 30) at thor base. They somefim~ e x ~ t a Nack tip (Pla~ I, 7, a~ow; Pl~e HI, 8). Vegetative axes bearing compara~e em~gences
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and showing K- and H-branching were found spread among the ~rtile specimens, but not in organic connection with them. They could represent the vegetative and/or the basN part of the plant. Vegetative axes with spiny NrNna~ tips are rar~y found in the nNghbourhood of the ~rtile axes, but sever~ ~ o b i h themselves could be ~ h t l y curved (Plate H: 7; Plate HI, 10-12). M o ~ of the spedmens show one or two dichotomies at the base of the ferfi~ re~ons (Plate I, 1-5; PlateH, 1, 3; PlatelII, 1). Th~ resul~ in four ~robifi of sporangia in organic connection (Plate I, 1-2). In a ~ven ~robilus, the sporangia are compactly inse~ed. Sometimes, a ~ w sporangia are found slightly b d o w the dichotomy (Plate I, 5, arrow). M o ~ ~robifi show a slightly curved (circinate~ dist~ part (Plate II, 7; Plate HI, 10-12). One spedmen exhibi~ a ~rob~us ending di~ally in a portion of axis devoid of sporangia (Plate H, 2-3, arrow), and maybe devoid of spines too (Hate H, 2). U n f o ~ u n a ~ , this spedmen ~ cut off d i ~ , but R is assumed that no fu~her sporan~a exi~ed above. The ~ngth of the ~robifi is at least 35 mm; thor width including sporangia ranges from 3 to 4mm. Sporangial morpho~gy and arrangement: Each spor a n ~ u m ~ borne by a distinct, spiny, ~Mk (Hate L 6; Plate H, 4-5). These ~ k s are inse~ed on the a~s of the s~obilus with an angle of 45-80 ° (Plate H, 4-5). They are then curved upwards di~ally, so that lhey hold the sporan~um more or
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~ss erect. They are 0.5 to 1.0 mm wide at thNr base; the ~ngth of thNr horizontal pa~ varies ~om 1.0 to 1.7 mm. The sporanNa were probably reniform in face view (Plate L 6; Plate III, 2, 5), but they are most oRen more or ~ss folded (Plate H, 4-5), appearing then approximately P-shaped (Plate I, 6; Plate HI, 3, 10) cr semicircuhr, with bas~ lobes well devdoped (Plate I, 6: PlateH, 4). Thdr hdght ~ 2.0-3.7mm (X= 2.62 mm; n = 30) and thor width ~ ~6-3.0 mm (X=l.7rnm; n=30). Considering that they are o~en folded in various ways, this measure ~ cert~nly underestimated and probably ranges ~om 1.5 to 4 mm. Sever~ spedmens tend to show that lhe sporan~a were made of two v~ves of equ~ ~ e (Plate I, 6, arrow; Plate H, 4, 6, 8-9; Plate III, 6; Figs. 2-3), and that spines were borne on the abaxi~ v~ve (Pla~ II, 6; Fig. 2). In a ~ven ~robilus the sporan~a are borne o p p o ~ l y to ~ r n a t d y in two vertical rows (Plate I, 4, 6; Fig. 3a). The two tows of sporan~a are placed at 100-150 ° on the a~s. The ~robilus thus shows a ~ue bfla~rM symmetry (as opposed to radi~ symmetry with two rows 180° apart-see bdow). Consequently, the s~obilus has a v e n ~ ~de (that one bearing the sporan~a) and a dorsal ~de. The ~robi~ can be seen tither in face view (Hate I, 6; Fig. 3a) or in various later~ ¼ews (Hate II, 6-7; Fig. 3b-d) or in dors~ view (Hate III, 2; Fig. 4). The strobflus of spedmen ULg M 13505 (Hate HI, 2-5; Fig. 4) is observed
I
Odo~ax b o m d ~ Gerfienn~ gen. et sp. no~ L ~ Forges ~cality, M a n ~ Bd~um. Lower Devo~an (early Emsia~. 1. ULg M 13374 P (= pa~). x 3. 2. ULg M 13374 CP (= coun~rpa~). Spe~men showing two iso~mi~, and four compact ~robdi ~ organic connectiom × 2.5. 3. ULg M 13361 P. × 2. 4. ULg M 13361 CPa. Ho~type. Branc~ng sy~em of ~rffie s~ny ~otomous and an~otomous axes. O~y lhe top (m~nly the strobili) c f the specimen ~ true part and counterpart; the axes have teen both uncovered and thus are not ~ orga~c connection. The a~ow ~ 3 ~ c ~ the position of the counterpa~ b ~ee 7), w~ch bears a suba~llary branch at the anisotomous branc~ng p~nt. T~s subaxillary branch ~ underneath the axes ~ N e on 3, but can be seen ff the counterpar~ a and b a n ~ p a r ~ e d ~ee 7 and Fig. 1~. On ~ the a~ow shows the position of another subaxillary a~s (~e Fi~ lb). x 2. 5. ULg M 13366. lso~mous ~rtile axis, wilh a sporang~m bdow the branching p ~ n t O~ow). × 3. 6. ULg M 13361 CPa. H ~ o ~ p ~ E~argement of the ~ p of the specimen, showing ~ v ~ sporanDa ~ ~ r M flew, and one appro~mately ~ ~ce flew ( ~ the ~ w ~ t pa~ of lhe figure). N o ~ thor bas~ ~ b ~ . The a~ow po~ts to the pofifion of the de~scence ~ne (the two v~ves of lhe sporang~m a n probaNy of equ~ s~e). x 10. 7. ULg M 13361 CPb. H ~ o ~ p e . Coun~rpa~ ~ showing a spiny subaxillary branc~ downward~ directed. The arrow shows an enafion with a ~ack tip. × 12.
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~om Rs dors~ fide. Fig. 4 ~ a ~ne drawing of this spedmen: R aids in the in~rpretation of Rs orientation. Having been probably displaced during the fo~ilisation proces~ some sporan~a appear to be more or ~ss covered by thdr st~k (Plate IH, 3-4). This bflater~ symmetry of the ~robilus ~so expl~ns why some other specimens seem to have a fin~e ~ow of sporan~a (Plate H, 6-7). In that case, the second row can still be buried in the sediment of the part or lhe counterpart. The specimen ULg M 13368 (Plate II, 7) shows at arrow a fragment of one sporan~um of this hidden second row. The aspect of this spedmen ~ tentativdy explained in Fig. 3a and d ~ee b d o w for fu~her explanation). The sporan~a rardy seem to be borne at 180° ~ o m each other (Plate III, 6; Fig. 3~, and this feature is interpreted as due to the compresfion. Because of the very poor preservation of the plant, R has been very ditticult to unde~tand the construction pattern of the ~robi~ and to build a modal that could explain thdr various aspects. The specimen ULg M 13504 illu~rated on Plate II, 6, 8-9 and in Fig. 2 was found the mo~ informafive. Even though R seemed impossible to expl~n R at first fight, R has allowed me to give the following in~rpretation of the s p o r a n ~ a~angement. This spedmen has proved very useful in unde~
95
~anding (1) the way the sporan~a are borne, (2) the position of the dehiscence ~ne and (3) the di~ribution of the spines on the sporangi~ (1) This spedmen bears all Rs sporangia on one fide of Rs axis only (Fig. 2). R thus might appear to have borne a fin~e row of sporan~a. However, every other sporangium shows a sinuous white ~ne (i.e., matrix), separating R into two equ~ h~ves (Plate H, 8-9; Fig. 2, arrow~. The two other ~poran~a are covered by thor ~ k . Fig. 3a-c explains how this spedmen might have been formed. The arobilus bore initially two rows of sporan~a at ± 120° (Fig. 3a). R has then been deposited whil~ rotated at an an~e of 60 °, as illu~ra~d in Fig. 3b. Then the s p o r a n ~ ~ k s have been caused, by the compre~ion, to bend slightly so that the sporangia were pushed on one fide of the a~s (Fig. 3c). In the speomen of Fi~ 3c (as in specimen ULg M 13504), the sporangia are placed in a looser manner then in the others. This feature, together with the compresfion, ~ probably responfible for the apparent arrangement of the sporan~ a in only one row. No other specimen shows such preservation. (2) The finuous white ~ne (Plate H, 8-9; Fig. 2, arrows) ~ considered to be an opening in the sporangium. It is therefore in~rpr~ed as the dehiscence ~ne, viewed ~om a di~al position. The modal (F~. 3a) was built with sporan~a made of two valves of equ~ fize. It has permitted
PLATE H Odonax b o r ~ Gfffienn~ gen. ~ sp. ~o~ Les F o ~ ~cality, M ~ c h ~ , Bd~um. Lowff D e v o ~ n ~ Em~an). 1. ULg M 13368 ~ x 3. 3. ULg M 13368 CPa. Sp~imen ~owing two compact strobifi; one of them (3, a~ow) e n ~ ~ a l l y ~ an a ~ s devoid of ~ o r a n ~ a . x3. 2. ULg M 13368 CP~ E n l a r ~ m e ~ of the ~ p of ~ e ~ i m e n ~ 3. The ax~ bears no sporan~a and ~ o b a b l y no s ~ n ~ . x 6. ~ ULg M 13366. En~rgemem of ~a~e L 5 showing a ~ o r a n ~ u m with its spiny slal~ b e ~ u p w ~ d ~ and ils ~ y ~baxi~ v a l e . Note ks bas~ ~be. x 16. 5. ULg M 13374 CP~ E ~ g e m e n t of ~ a ~ L 2. The sporan~um bears spines on its a b a ~ v~ve. x 15. 6. ULg M 13504. Sp~imen w i ~ ks sporan~a ~ r a n ~ d ~ one row ~ee ~so ~ g . 2). E v e ~ o ~ e r sporan~um shows a ~nuous open~g (position of ~ e d e ~ s ~ n ~ fin~; ~ e o ~ f f ~ o m n ~ a ~ e cove~d by ~ d r ~ ~ g . 3a-c explains my ~ r e t a t i o n of ~ specimem x 4. 7. ULg M 13368 CPb. Sfighfly distally cu~ed (~rcin~e?) strobil~, show~g one row of ~ a n ~ a . The ~ h e r mw ~ buried ~ the ~diment of ~ e c o u n ~ but one of its ~ a n ~ a ~ ~e O~ow). x ~5. 8. ULg M 13504. Enl~gement of 6, ~owing two sporan~a. The ~wer one ~ an openin~ the upper one ~ cove~d by ks st~k. Note the s p i e s on the a b a ~ v~ve of the ~ o m n ~ a ~ee ~ g 3c ~ r the i n t e ~ t a t ~ n of this ~ i m e ~ . x 10. 9. ULg M 13504. E ~ a r g e m e ~ of 6, ~owing one ~ a n ~ u m . Note the ~nuous open~g ( p ~ o n of the d e ~ e n ~ fine), and the s~nes on ~ e a b a ~ v a l e . x 10.
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P. Gerrienne/Reviewof Palaeobomny and Palynobgy 93 (1996) 89-106
PLATE III
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to obtain an image (Fig. 3c) very dose to that shown by the specimen ULg M 13504 (compare Fig. 3c and Plate II, 6). So I think that the plant had sporanNa with valves of equal ~ze too. Another speNmen (Plate III, 6, arrow) show an opened sporangium, (3) SpeNmen ULg M 13504 also ~lustrates spines, borne by the sporangia on Rs abaxial valve only (Plate H, 8-9; Fig. 3b-c). The adaxial valve of the sporangium is devoid of spines (Plate II, 8-9; Fig. 3b-c). Because of the poor preservation of the plant, no anatom~al data about Rs internal ~ructure or Rs spores could be obtained. Neve~h~ess, the ~udy of the morphology of spedmens vafiou~y disposed in the sediment has permitted to give a reconstruction of the fe~i~ axes of the plant, presented in Fig. 5.
Comparisons The morphological characteristics of Odonax conform to those of the Zosterophyllophytina and the new genus is therefore included in that subdivifion. Together with Odonax, the ZosterophyHophytina include twenty genera. Table 1 shows a comparison of sdected morphologicM data of all the zosterophylls. In Odonax, two characters (the dorsiven~al ~rob~us and the spiny abaxial valve of sporangium)appear highly discriminating, bNng not reposed together ~om other genera ~ee Table 1). Neve~he~ss, I think that a more detailed comparison with Rebuchia and Sawdon~ is necessary,
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97
If the new Bdgian plant did not bear enafions (but see bdow), R would be very dose to Rebuch~, mainly because of the branching pattern, a~oNaled with the b~ateral symmetry of the ~robilus. Unfo~unately, R ~ not easy to compare Odonax and Rebuchia, because the morphology of the latter ~ not fully understood. For example: (1) Which is the exact form of the sporangium of Rebuchia? (2) Are these sporangia sessile or borne by a very sho~ ~alk? (3) If they are presenL are the stalks of the Rebuch~ sporangia inse~ed on both fide of the axis, then bent towards one fide of it, or are they inse~ed directly on one fide of the strobilus axi~ Hueber (1972a, p. 118) writes "the sporangia (...) are directed by curvature of thNr stalks toward one fide of the axis (...)", which probably means that the two rows of ~alks are 180° aparL but both the photographs (Hueber, 1972a, pl. II, 4), and the recon~ruction of the plant (Huebe~ 1972a, fig. 1) suggest that the stalks were borne on only one fide of the axis. As already suggested by several authors ~.g., Gensd, 1982b; Niklas and Banks, 1990), Rebuchia is ~m~ar to some Zosterophyllum speNe~ and mo~e p~eNsdy to Z. spectabile Schweitzer and Z. divaricatumGensd. We definitely need the answers to the above questions (and probably to some others) to deNde whether Rebuchia should be placed in synonymy with Zosterophyllum or not. Neverthdess, apart ~om the presence of emergences, subaxillary branch and stalks bent upwards
PLATE III Ge~ienne, g e ~ ~ sp. no~ Les Forges localit~ M a m ~ Bd~um. Lower Devo~an (early Em~an). 1. U [ g M 13374 P. Four badry p r e ~ e & slightly c u ~ e ~ strobili ~elonging probebly u the ~ e specimem x 2.5. 2. ULg M 13505. S~ke approximately ~ewed from d o ~ ~de. The b ~ of ~ e s~ny ~ k s am deafly ~ b ~ ~ ~ g . 4). × 5. 3-5. ULg M 13505. E ~ g e m e ~ of three sporan~a of the spedmen ~ 2. Those ~ 3-4 am ~dden by thor ~ k and the axis; ~ e ~ o m n ~ u m ~ 5 ~ not ~lded and shows hs mnfform shap~ x 12. 6. ULg M 13~06. Fettle axis ~owing two o p p o ~ ~ o r a n ~ 180 ° apa~ (probably b~ause of compression: see ~ g . 3~. Arrow ~ c a ~ s ~ e ope~ng ~ the ~ o r a n g ~ m , ~ ~ m r ~ ~ew. x 10. 7. ULg M 13368 P. S~ne showing a c u ~ e ~ w ~ d s the Up of ~ e spedmen, x 20. 8. ULg M 13374 P. T r i a n g ~ spine with ~ a c k tip. x 20. 9. ULg M 13374 P. S~ne ~owing a cu~e U w ~ d s the base of the spedme~ and a black tip. x 20. 10. ULg M 13505. Di~ally c u ~ e d ( c i r c i n a ~ strobilus, w i ~ o p p o ~ sporan~m x 7. 11. ULg M 13505. Enlargemem of ~ e cu~ed ( c i r c i n ~ ) Up of the specimen ~ 10. A ~shaped ~ o m n ~ u m ~ ~ s ~ . × 14. 12. ULg M 13368 CPb. E ~ a r g e m e ~ of the cu~ed (circin~e~ top of the ~ i m e n on ~ e II, 7. × 11. Odorax boma~
98
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~ g . 1. Odonax b o r ~ Gerrienne, gen. et ~ no~ ~ne ~ a ~ n ~ of pa~ (a) and coun~rpa~ (b) of ~e h~o~pe (~e~men ULg M 13361 P and CP~b). ~ e ~ e L 3-~ 7.
~ Ge~ienn~Reviewof Palaeobomnyand Palyno~gy 93 (1996) 89-106
the species Sawdonia ornata (Dawson) Hueber. When S. acanthotheca Gensel et al. and S. spinos~~irna Schweitzer have sporangia spread along the axes, S. ornata might exhib~ loose strobili (Rayner, 1983). Nevertheless, the comparisons are difficuR, because the morphology of the fertile regions of that species should be clarified. The shape and the distribution of ~s sporangia are not clearly defined: compare, for example, the fertile specimens as~gned to Sawdonia ornata in Gensel and Andrews (1984, fig. 4.47), in Schweitzer and Heumann (1993, figs. 5-6), and in Hueber (1992, fig. 3B) wRh those of Rayner (1983, figs. lb and 7). Anyway, as far I can judge, the compact strobili, the strong spiny stalks, and the reniform sporangia of Odonax look quRe different from those of Sawdonia. Even though the specimens of Odonax are badly preserved, the creation of a new genus appears justified because this plant show a set of characters (spiny axes-compact strobfli w~h a bilateral symmetry-sporangium wkh two valves of equal size, the abaxial one being spiny, borne by a spiny stalk bent upward~ which have not so far been found together in an Early Devonian plant.
~
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~
99
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Figo ' fthe" spedmeOd°nan x borealis G,e r rLM i e 13504 ngn e u (~gee~Ilet,sP'5)~°~ee Line draw~al g s Fig. o 3c for an ~rp~mfion of t~s specimen. A~ows show the sporan~a opened ~to two equM v~ve~ the a b a ~ one bong spiny,
separate Odonax from Rebuchia and these characters strengthen my deci~on to erect a new genus for the Belgian specimens. The other genus with which Odonax might be related ~ Sawdonia Hueber, and more precisely
Presence ofenations
The taxonomic weight to be accorded to the presence of a given character is crucial to separate and delim~ taxa. Workers seem to agree that ~ze ~ not a re~able characte~ and the observation of for example the size of leaves or fruits in modern plan~ demonstrate clearly large pos~ble variations even within the same individual. Among the first land plants, a definitely more useful character in delimiting taxa is the presence or absence of nonvasculafised emergences, but the treatment of ~ depends on the group with which one ~ dealing. As akeady noted by Kenrick and Edwards (1988a, p. 108), the presence/absence of enations ~ used as a specific character among the Tfimerophytina and as a generic d~fincfion in the Zosterophyllophytina. Anyway, I do not think that any of the already described zosterophyll genera would be placed in synonymy, if enafions
P. Gerrienne/Reviewof Palaeobotany and Palynology 93 (1996) 89-106
100
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Fig. 3. I~u~rafions of different possible aspects and orientation of the strobil~ for each, a ~mplified ~ansverse section ~ drawn,
showing the r~afive position of the axis (A), and two consecutive sporangia (SP). (a) Recon~ruction of a incomplete grobilus of four sporangia in hypothet~al ~fe position. The sporangia are borne on one ~de of the axis and the s~ob~us seen in ~ont view. (b) The same as in (a), but after a 60° rotation, one row of sporangia N seen in ~ont view. This orientation has not been observed. (c) The same as in (b), but the sporangium in the ~ont has been displaced during fossilisation (only two sporangia are drawn). This drawing i an interpretation of speNmen ULg M 13504 (Plate II, 6). Note the Nnuous dehiscence hne and the spines on stalks and abaxial valve. See fu~her explanation in text. (d) The same as in (a), but a~er a 150° rotation: one row of sporangia ~ exactly seen in lateral view. Interpretation of speNmen ULg M 13368 (Plate H, 7). (e) The two rows of sporangia seem to be 180° apa~ because of the compresNon. Interpretation of specimen ULg M 13506 (Plate III, 6).
were a d d e d (or suppressed) to a n y o f them. F u r t h e r m o r e , it appears that the presence of e n a t i o n s in zosterophylls ~ ~ s s i m p o ~ a n t t h a n t h d r a c t u ~ form a n d dis~ution. I n the case o f Odonax, the t r i a n g u l a r shape, the small fize a n d the d i ~ f i b u f i o n o f the e n a f i o n s a r o u n d the axes, o n the ~ k s , a n d o n the a b a ~ v ~ v e s o f the s p o r a n ~ a are quite distinctive. These characters, a l l ~ d with the presence o f subaxillary b r a n c h e s a n d c o m p a c t ~ r o b i f i with d o r s N e n t r a l m o r p h o l o g y
~ d me to deride the creation of a new genus rather t h a n asfigning m y s p e d m e n s to the genus Zosterophyllum. N e v e ~ h d e s s , I t h i n k that the p r e ~ ence o f e n a t i o n s should n o t ipso f a r o exclude a n y s p e d m e n from Zosterophyllum. ~Z
Bila~ral or radial symmetry of the ~robilus
A strobilus showing bilateral s y m m e t r y m a y be d i f i d e d into two e q u ~ h ~ v e s b y only one longitu-
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dinal plane. A s~obilus having two rows of sporangia 180° apart ~ capab~ of bNng divided into two equal halves by two longitudinal planes and therefore should not be said to show bilateral symmetry. The bilateral versus radial arrangement of the sporangia has already been discussed at ~ngth. Many authors still think k useful in dehmiting taxa (for example, Gensd, 1982b). On the contrary, Niklas and Banks (1990, p. 276) have recently considered Zosterophyllum fertile and Z. divarkatum ~ome of the "bilateral speoes') to fit with the radially symmetrical forms. In 1988, I wrote that "maybe these two arrangements (bilateral or spiral) did not exist in the riving plan~: a bilateral spike may be ju~ a spiral one with a few sporangia' (Gerfienne, 1988, p. 328). Today, I con~der that the conNstency of the bilateral symmetry of the specimens of Odonax suggests that the bilateral arrangement did exist in some plants, Of course, ~ still remains true that other taxa could probably show a bilateral symmetry ju~ because of preservafion~ but in the case of Odonax at Last, and probably of Rebuch~ and some Zosterophyllum, I am convinced that the sporangia were borne in this way by the plants,
~ Fi~ 5. Odonax borealis Gerrienne, gen. et ~. Recon~rucfionof the ~r~e re,on of~e ~am. L~
no~
Definite or indefinite growth
Among~ the spedmens of Odonax, some end in a ~robilus (and thus presumably in a sporangium) whereas at ~ast one probably ends in an axis devoid of sporangia. Niklas and Banks (1990, p. 277), in as~gning speNes to Nther terminate (ending in a sporangium: definite growth) or nonterminate (ending in an axis: indefinite growth) forms, chose to give priority to this character over the symmetry of sporangial arrangement. ThNr two arguments were (1) the difficulty to disfingu~h
~ Gerrienne/Rev~wof Palaeobomny and Palynology 93 (1996) 89-106
102
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P. Gerrienne/Review of Palaeobotany and Palynology 93 (1996) 89-106
morpholo~cal symmetry for fossil ~ructures and (2) the absence of unambiguous evidence for the symmetry of the arrangement of primordia on apses. So they derided to base thor anNyfis on the defini~ or indefini~ growth of the apices of fertile axes. Neve~hdess, I ~ d that this character should not be overestimated. I believe indeed that the largest m~ority of the fllu~ramd ~rtile axes of zo~erophylls are not complete and that k ~ Nmo~ impossible to know wh~her they ended in a sporan#um or in an axis. For exampl~ Z. deciduum (described ~om Marchin, the same locNky as Odonax) is asNgned by Niklas and Banks ( 1990, table 1) to the Zosmroph~lophyfina with ~rminate ~rtile axes. Yet the only spedmens of Z. deciduum to show a preserved di~N part are the counterpart of the holotype (Gerfienne, 1988, fig. 1D, pl. IV, 2) and the spedmens ULg M 13154 ( G e ~ n n e , 1988, pl. I, 9-10) and ULg M 13162 (Gerrienne, 1988, pl. IV, 4, 7). These three spedmens do not end in a sporan#um, and thNr very di~N ~a~ is the mo~ probably an a~s rather ~han a stNk. All the other spedmens of Z. dedduum are incomplete at thor distN extremity. So, R seems to me that Z. deciduum should be~er be included in the non~rminate zos~rophylls. This fact, all~d Io the difficulty of making judgements from sometimes poor illus~ation~ ~ads me to believe that severn other taxa might Nso be nonterminate rather than ~rminate or even both mrmg nam and non terminal, and, consequentl~ that this di~inction ~ even harder to use than the radiN or bilaterN disposition of the sporan~a, Moreove~ examining the two tables ef Nik~s and Banks (1990), R appears that thor distinction b~ween ~rminate and nonterminate goes more or ~ss exactly together with the d~tinction '~nding in a strobHus or nof'. There are two exceptions to this ru~ in thor fable 2, but they are poorly preserved spe~mens and may be mifinterpreted: these are Sawdon~ ornata and Ba~ur~& denticu&ta, which may show ~robili ~ee Rayner (1983) for Sawdon& and Hueber (1972b) for Bathurstia]. It ~ not obvious that a plant ending in a strobilus has a terminate growth. Examples taken from riving plants ~ n d to show that the di~inction b~ween terminate and nonterminate ~rtile axes ~ far from dear:
103
(1) Among~ the extant Lycopodium spedes, some are ~rob~ate yet nonterminate (Bierhorst, 1971, p. 15, fig. 2-5D--this spedmen is ~robila~ and however looks nonterminate; Niklas and Bank~ 1990, p. 281). (2) In the Magniolophyta, the--sometimes compact--inflorescences can be indifferent~ ~rmP nate or nonterminate ~ee, for example, Bell, 1993, fig. 141). As a fu~her example among many: severN cultivars of An~rrh~urn L. show racemes with definim growth ingead of the racemes with indefinile growth of the wild indi~duNs. The mechanisms of the differentiation of ~rtile ~aves or flowe~ on the one hand, and of sporanNa on the other, are probably different. However, because of the reasons rehearsed above, I believe that too much empha~s should not be #ven to this mrminate-non~rminam di~inction, and that this charac~r is probably us~e~ for delimiting taxa at the generic Mv~ at Ma~.
~
Presenceofa subaxillary branch
Among the Zos~rophyllophytina, seven genera have a subaxillary branch (Table 1). These are Gosslingia, Crenatieaulis, Margophyton, An&ophytom Thr&kophyton, Deheubarth& and now Odonax. Hass and Remy (1986) have provided severn observations about these subaxillary branches (they call them "Angula~Organs'3. They espe~a~y draw our a~enfion on the assumption that the only genera showing this subaxilhry branch are those with a planar aefiN a~s sy~em. Observations about the anatom~N ~atures of Gossling&(Edward~ 1970; Kenfick and Edward~ 1988b) and Deheubarth~ (Edwards et N., 1989) have shown that the subaxiHary branch belongs to the axiN sy~em and ~ thus not comparab~ with an adventitiousroot(Edwards~N., 1989, p. 314). In the same pape~ these authors noted that in Deheubanh& and An&ophymn (where the anatomb cN data are lacking), this interpretation is ranforced by the presence of spines on the subaxillary branch. Odonax has spiny subaxillary branches too. These la~er are thus probably closer to those of An&ophyton and Deheubanh& than to those of Crenaticaulis.This la~er genus indeed has spiny axes and naked subax~lary branches, which are,
P. Ge~ienne/Rev~wof PaMeobotanyand Palynology93 (1996) 89-106
104
according t o B a n k s a n d D a v i s ( 1 9 6 9 ) a n d E d w a r d s et al. (1989), probably closer to the rhizophore of Selaginella than to an axis. The presence of this subaxiHary branch in some zosterophyll genera N interpreted by several authors as a further indication of the rink between the Zo~terophyllophytina and the Lycophytina. From that point of view, be this organ tither an adventitious root or an axis does not matte~ since several lycopods (Selaginella for example) show both these two organs. The angle meri~em of this plant may indeed develop either into a rhizophore when the apical meristem is presenL or into an axis, when the apical meristem has disappeared (Cusick, 1953, pp. 369-370, 1954, p. 171).
6.
Condu~on
The specimens described here exhibit a set of characters (for example, the bilateral symmetry of the strobir and the reniform sporangium with a spiny abaxial valve) nct previou~y seen together among the zosterophylls. The creation of a new genus thus appears fully justified. At first fight, the specimens of Odonax seemed too badly preserved to interpret the variable aspects of the strobili. Nevertheless, a fairly good understanding of their morphology has yet been obtained, in that the various aspects of the fossil are explained by the bilateral symmetry of the strobili. This "prese~ vafional effect" (the complexity and/or the asym-
metry of the plant induce different or~ntafions during fossilisation, which in turn allow the understanding of the initial architecture of the plant) is oRen exploited in palaeobotany and is sometimes the only way to obtain predse morphological or anatomical information from poorly preserved specimens.
Acknowledgements I am pleased to have this opportunity ofdedicating this paper to Professor Maurice Stred, for his outstanding contribution to palynology, and for his kindness and generoNty to me during all these years.
My thanks are also due to Christopher M. Berry, for his constructive comments and h~p, and to F e r Giraldo, who made the drawings.
References Bank~ H.P., 1968. The early history of hnd ~ants. In: E.T. Drake ( E ~ O , Ev~ufion and En~ronment. Symp. 100th Hi~oryA .nn~Sa~aY~FoundatiOu n ~ vPres~O~ew . HaveP meabody Musuec m TPP. , 73_107o . fN~ur~ Bank~ H.P., 1975. Rech~cafion of Psi~phyta. Taxon, 24: 401-413. Bank~ H.E, 1992. The das~ficafion of early Nnd Nants-~d. P~aeobo~st, 41: 36-50. Banks, H~. and D a ~ M.R., 1969. CrenaticaM~ a new genus of Devo~an ~ants all~d to Zosterophyllum, and ks beating on the das~ficafion of early hnd ~an~. Am. J. B~., 56: 436-449. Bank~ H.P., Bonam~ EM. and Gfi~son, J.D., 1972.
thLeec&~qlaiateM~COempleX~evo~agnen. et speCo, f cavern nOV.,a Nen weW~cOpOyo drk" Rev~ .ore P~aeoboL P~yn~., 14: 19-40. Bell, A.D., 1993. L~ Hant~ fi F~urs--G~de Morph~o~que n~. M~so~ Faris, ~41 ~p. (French translation. Bi~horst, D.W., 1971. Morpho~gy of VasSar Nam~ CufikM ,acmffianF , . , 1953N .ew ExpefimentYO M rNY, ~ 560anPd p. ana~ficN ~ u ~ of P~fidophy~s. xxII. MorphogeneNs~ Selaginella wildenovii Bake~ I. Preliminary morphNoNcN anNyNs. Ann. Bot. London, 17: 369-383. Cu~k, F., 1954. ExpefimentN and analyt~N ~ u ~ of Ptefidoph~. XXV. Morphogenesis~ Selaginella wildenovii Bake~ ft. Angle-meristems and anN~shoo~. Ann. Bot. London, 18: 171-181. Edwards,D., 1969. Zosterophyllum ~om the Low~ ON Red Sand~oneof South Wa~s. New Ph~M., 68: 923-931. Edward~ D., 1970. Fu~h~ ob~rvafions on the Low~ DevoNan rant, Go~ling~ breconensis Heard. Philos. Trans. EdwardR ~Soc. . D.,ondonl L ,975.258S :om~25-243o .bservafions on the ~rNe pa~s of Zosterophyllummymtonianum Penhallow from ~e Low~ Old Red Sand~one of Scotland. Tran~ R. Soc. E~nburgh, Edward~ 9:a251-265D s, " and . KenficL P., 1986. A new zos~rophy~ ~om the Lower DevoNan of Wa~s. Bot. J. Linn. Soc., 92: 269-283. Edward~ D., Kentic~ P. and Caducd~ L.M., 1989. A ~cons~afion of c£ Psilophytonpr&ceps (Croft and Lan~ lg42), a zos~rophyll widesp~ad ~ ~e Lo~er Old Red Sand~oneof South Wa~s. Bot. J. Linn. Soc., 10~ 293-31L Gensz d,osterophyllophy~P s . G .1982a. , Or~ilafr,om ~ea~tneeWeaflgyenUi~evo~a~ n~raN~fno~ht _ othe ~n New Brunswick. R¢v. PNaeoboL PMynN., 37:345 359. Gensd, P.G., 1982b. A new spedes of Zosterophyllum from
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105
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