FLORA OF THE SAINTE-ANNE FORMATION

The study of Devonian plants from the Sainte-Anne Fm started with Bureau et al. [1908]

when they named the deposits in which they discovered fossil plants as “Sainte-Anne sandstone with Psilophyton princeps Dawson”. In these deposits, Bureau et al. [1910] and Bureau [1911, 1913] reported the occurrence of P. princeps (Châteaupanne quarry, Le Petit Fourneau, La Maison-Neuve, Sainte-Anne quarry), Bornia transitionis Roemer (Sainte-Anne quarry) and Lepidodendron gaspianum Dawson (Le Fourneau Neuf, Chaudefonds).

Carpentier [1920] attributed the plants he collected (Sainte-Anne quarry) to Psilophyton Dawson, P. princeps Daw. and P. spinosum Potonié & Bernard. Later, he suggested that those fragments could be related to Asteroxylon elberfeldense Krausel & Weyland [Carpentier, 1927]. He also reported the occurrence of Hostimella sp. Lang (Châteaupanne) and Asteroxylon elberfeldense Kr. and W. (Châteaupanne and Saint-Charles quarry) [Carpentier, 1928, 1931]. Finally, Couffon [1909; 1934] listed the plants studied by these authors.

The aim of our study is the revision of this flora and the description of new samples collected from the Sainte-Anne Formation (our specimens and a few samples coming from collections in the Natural History Museum in Angers) (tabl. IVa-6). Additional information obtained by palynological analyses will be briefly summarised.

TABLE.IVa-6. – Systematic revision of the flora of the Sainte-Anne Fm.

TABL.IVa-6. – Révision de la flore de la Fm de Sainte-Anne.

Previously described flora from the Sainte-Anne Formation

The flora previously described by Bureau et al. [1908; 1910], Bureau [1911; 1913] and Carpentier [1920; 1927] had to be revised according to what is currently known about Devonian plants. Presently, the specimens belonging to the Bureau collection are housed in the Natural History Museum in Nantes and those from the Carpentier collection are kept at the Catholic University in Lille.

Hostimella

Today, the genus Hostimella represents a catchall genus for naked dichotomous axes of unknown affinities from the Devonian age. These axes were collected from the Sainte-Anne Fm and were named Hostimella sp. Lang by Carpentier [1927]; they were associated with Asteroxylon elberfeldense. Hostimella has sometimes been considered as isolated branching fragments of Margophyton (= Psilophyton) goldschmidtii, now believed to be a Lower Devonian member of the Zosterophyllopsida [Zakharova, 1981]. Kräusel & Weyland [1926]

considered Hostimella hostimensis Pot. & Bern. as the naked terminal parts of Asteroxylon elberfeldense but this point of view was discussed by Fairon-Demaret [1967].

Asteroxylon elberfeldense

Carpentier [1927, 1928 and 1931] reported the occurrence of Asteroxylon elberfeldense Kräusel & Weyland 1926 in the Sainte-Anne Fm. The specimens illustrated by Carpentier [1920, Pl. I, fig. 1 to 11; 1928, Pl. I, fig 2 and 3; 1931, Pl. I, fig. 3 to 16] compare well with those of Kräusel & Weyland [1926, Pl. 3 and 5]. However, Carpentier did not observe the essential diagnostic characters of Asteroxylon, namely scale-like enations, caulinary sporangia and a distinctive lobed stellate xylem strand.

Lepidodendron gaspianum

Lepidodendron gaspianum was the first plant collected by Bureau [1911]. Its name has been replaced by Drepanophycus gaspianus by Stockmans [1940].

Psilophyton

Bureau et al. [1908; 1910], Bureau [1911; 1913], Carpentier [1920], Couffon [1909; 1934]

reported the occurrence of various species of the genus Psilophyton (P. princeps, P robustius, and P. spinosum). These plants were not well-known at that time. Dawson erected the genus Psilophyton in 1859 for Devonian plants from the Gaspé Peninsula (Canada) that resembled modern Psilotum. He published the first complete description of the type-species P. princeps in 1871. Nowadays, the concept of Psilophyton is better defined.

1. P. princeps is the name applied to plants that have spiny axes with clusters of fusiform sporangia at the end of lateral axes. The specimens with spiny axes showing globose and caulinary sporangia, originally described by Dawson as P. princeps var. ornatum, are referred to as Sawdonia ornata [Hueber, 1971].

2. P. robustius was originally described by Dawson [1871]. This species has been transferred to the genus Trimerophyton [Hopping, 1956]. The main stem of this plant is approximately 1.0 cm wide and bears numerous helically arranged, trichotomous lateral branches.

3. P. spinosum was first described as an alga by Stur [1882]. Potonié & Bernard [1904] placed it in Psilophyton because of the occurrence of a central strand and emergences on the axes. P. spinosum has to be revised.

In summary, the plants from the Sainte-Anne Fm previously attributed to the genus Psilophyton are vegetative axes without anatomical detail. It is therefore impossible to confirm that they belong to the genus Psilophyton.

Bornia transitionis

Bureau [1913] reported that a diagnosis had not really been given for Bornia transitionis Roemer, but rather only complementary characters for the genus. Bornia transitionis gathered plants in which the specimens exhibit similar stems and leaves. Bureau provided numerous synonyms for this species (e.g. B. scorbiculatus, B. radiata, Calamites scorbiculatus, C.

radiatus, C. transitionis, Archaeocalamites radiatus, A. scorbiculatus) and considered that this plant was well represented with fertile organs in the Culm (Frasno-Dinantian) deposits from the Anjou area. From the Sainte-Anne Fm, Bureau et al. [1910] reported that thin filaments assimilated to leaves were attached to an axis portion and described them as Bornia transitionis. There are no specimens available (only citations in Bureau et al, 1910 and Bureau, 1911) and because there are no illustrations of the fertile organs, it is impossible to suggest a name for this specimen. Bornia transitionis is a name that is not currently used.

New study of the flora from the Sainte-Anne Formation

We collected samples from the Sainte-Anne and the Châteaupanne quarries. The most important part of the Sainte-Anne quarry is now flooded; only a small outcrop is accessible.

In the Châteaupanne quarry, the Sainte-Anne Formation outcrops in many places, but the material is badly preserved. Our specimens are housed at the University of Angers (Strullu-Derrien collection). Several samples from the collections of the Natural History Museum in Angers were also examined.

Several classifications have been suggested for early vascular plants; first by Banks [1968, 1975 and 1992], and more recently, by Kenrick & Crane [1997] based on a cladistic analysis. The phylogenetic tree presented here (fig. IVa-10) is a compilation of recent data [Kenrick & Crane, 1997; Pryer et al., 2001; Gerrienne et al., 2006; Hilton & Bateman, 2006;

Gerrienne, 2008]. The description of the flora from the Sainte-Anne Formation is presented within the framework of this phylogenetic analysis. In the Sainte-Anne Fm, plants occurring in sandstones are usually floated specimens preserved as compressions /adpressions (fig. IVa-11A).Our study shows the occurrence of plants belonging to three clades (fig. IVa-10). A comparison between the two flora is presented in tabl. IVa-6.

Hostimella

its presence is not significant, as such naked dichotomous axes may belong to a wide range of Lower Devonian plants.

Lycopsid and detached microphyll

Several axes ranging from 2.5 to 3 mm in diameter and showing a pattern of helically arranged fusiform scars were found in the sandstones. Those axes bear some resemblance to the Drepanophycus (Lepidodendron) gaspianus specimens drawn by Bureau [1911, fig. 2, Pl.

1 and 1913, fig. 2, Pl. I bis]. They also compare well with early Lycophytes such as Asteroxylon [Fairon-Demaret, 1967] or Haskinsia [Fairon-Demaret, 1981; Berry & Edwards, 1996]. Decorticated stems of Leclercqia [Berry, 1994; Meyer-Berthaud et al., 2003; Gensel &

Kasper, 2005], a late Lower to Middle Devonian lycopsid genus, may also show a comparable pattern of helically disposed fusiform leaf scars (Gensel, comm. pers.). Similarities among early Lycophytes axes in compressions/adpressions are numerous, with the result that it is frequently impossible to distinguish one partially preserved specimen from another [Bonamo et al., 1988]. When the leaves are not preserved, as it is the case here, identification of the genus is difficult (compare Figure IVa-11 B1 and B2 of this work to figure 45 on page 233 in Bonamo et al., 1988).

FIG.IVa-10. - Simplified phylogenetic tree of the embryophytes. Thick bars show the stratigraphic extension attested by the fossil record.

FIG.IVa-10. – Classification phylogénétique simplifiée des embryophytes montrant leur extension stratigraphique.

FIG.IVa-11. – (A) Sample from the Sainte-Anne Fm showing pieces of plants (loc. 8, tabl. IVa-1);

Natural History Museum collection, Angers. (B) Part (B2) and counter-part (B1) of a decorticated stem of a Lycopsid (loc. 8, tabl. IVa-1). Each fusiform pattern (arrow) corresponds to the attachment of a microphyll; C. Strullu-Derrien collection, University of Angers. (C) Structure of the microphyll-type that seems to fork into four segments: 3 complete segments and only a part of the fourth segment

(arrow) are visible on the figure (loc. 3, tabl. IVa-1); C. Strullu-Derrien collection, University of Angers. (D) Zosterophyllopsid (?) (loc. 8, tabl. IVa-1). Axis with trichomes (D1); circinate tip of an

axis showing small trichomes (D2); Natural History Museum collection, Angers. (E1) Two pairs of fusiform sporangia (loc. 8, tabl. IVa-1); Natural History Museum collection, Angers. (E2, E3) pieces of probably P-type tracheids (loc. 3, tabl. IVa-1); C. Strullu-Derrien collection, University of Angers.

(F) . Spore: Apiculiretusispora plicata (loc. 8, tabl. IVa-1); C. Strullu-Derrien collection, University of Angers.

FIG.IVa-11. – (A) Niveau à plantes de la Fm de Sainte-Anne. (B) Empreinte (B2) et contre-empreinte (B1) d’une tige décortiquée de Lycopside. (C) Structure de type microphylle dont l’extrémité semble se

diviser en quatre segments : 3 complets et une partie du 4ème (flèche). (D) Zostérophyllopside (?) (D1) Axe porteur de trichomes ; D2) Extrémité circinée d’un axe portant de petits trichomes. (E1) Deux paires de sporanges fusiformes ; (E2, E3) Fragments de trachéides probablement de type P. (F)

.Spore : Apiculiretusispora plicata.

A dispersed microphyll-like structure was collected in the Châteaupanne quarry (fig.

IVa-11C). The structure seems to fork into four segments (three complete segments and only a part of the fourth segment (arrow) are visible on the figure). The leaves of several Estinnophyton species (early Sphenophyte?) [Fairon-Demaret, 1979; Hao et al., 2004] are known to bifurcate twice and hence, to have 4 segments, but these are longer than the segments of the leaf-like structure from Châteaupanne. The latter can be compared with the microphylls of Colpodexylon [Banks, 1944; Berry & Edwards, 1995] which fork into three segments, and to those of Leclercqia [Banks et al., 1972; Meyer-Berthaud et al., 2003; Gensel

& Kasper, 2005], which show five segments.

Zosterophyllopsid?

Among our specimens, several pieces bear trichomes (fig. IVa-11 D1) and circinate vernation (fig. IVa-11 D2) is observed at the tip of the spiny axes. These characters are found in certain Zosterophyllopsids such as Sawdonia ornata [Hueber, 1971; Rayner, 1983] or Odonax borealis [Gerrienne, 1996], among other species.

Cf Psilophyton

Figure IVa-11 E1 illustrates two pairs of fusiform sporangia that are twisted around each other in each pair. This type of sporangia is characteristic of the genus Psilophyton [Gerrienne, 1997a] and is consistent with the presence of numerous anisotomously branched axes (from 0.8 to 8 mm in diameter). Some of these axes are devoid of emergences and show longitudinal ribs; a character found, among others, in P. forbesii [Andrews et al., 1968;

Gensel, 1979; Gerrienne, 1997b]. Moreover, fragments of tracheids were found in palynological slides. These tracheids show scalariform pittings and pitlets in the sheet between two successive thickening bars (fig. IVa-11 E2 and E3). They closely resemble P-type tracheids [Kenrick & Crane, 1997], which are characteristic of the genus Psilophyton.

However, these fragments are not well preserved and could also correspond to G-type tracheids (found in early Lycophytes). Nevertheless, it seems plausible that Psilophyton is represented in the Sainte-Anne Fm, perhaps by the species forbesii. The distinction between P. dawsonii and P. forbesii discussed by Gerrienne [1997b] shows that differences between these two species are few and it is possible that they are synonymous.

Spores from the Sainte-Anne Formation

Palynological studies of the Sainte-Anne Fm were initiated by Moreau-Benoît [1974]. Two kinds of isolated spores have been found: Leiotriletes sp. in sandstones from the Saint-Charles quarry [Moreau-Benoît, 1974] and Leiotriletes pyramidalis from shales in the east of Chaudefonds [Moreau-Benoît & Dubreuil, 1987].

We observed the following taxa in several of the samples from the Châteaupanne and Sainte-Anne quarries: Ambitisporites sp., Apiculiretusispora sp., Apiculiretusispora plicata (fig. IVa-11 F), Emphanisporites sp. and Retusotriletes sp. Most of these spore taxa are known to be produced by Emsian plants, amongst others. For example, Retusotriletes sp. is produced by Psilophyton princeps, P. dawsonii [Edwards & Richardson, 1996] or Sawdonia ornata [Rayner, 1983]; the two genera Retusotriletes and Apiculiretusispora are found in the sporangia of either Psilophyton parvulum [Gerrienne, 1995] or Renalia hueberi, a plant from Gaspé (Canada) [Edwards & Richardson, 1996]. Apiculiretusispora plicata has been observed within the sporangia of Psilophyton crenulatum [Edwards & Richardson, 1996].

Acritarchs from the Sainte-Anne Formation

Moreau-Benoît [1974] reported a few acritarchs in the Sainte-Anne Fm from the Châteaupanne, Saint-Charles and l’Orchère quarries. Veryhachium valiente (Cramer) is the most abundant species and several Veryhachium sp. have also been found. She described a new species (Synsphaeridium spinosum) and reported the occurrence of Synsphaeridium cf.

sorediforme (Timofeev), ?Ammonidium cf. alloiteaui (Deunff), Michrystridium ornatum (Stockmans & Willière) and Cymatiosphaera sp.

In our study of samples from the Châteaupanne and Saint-Charles quarries, the observed assemblages are mainly composed of ubiquist forms: Multiplicisphaeridium spp., Michrystridium spp., Veryhachium spp., Gorgonisphaeridium sp., Polygonium spp., Buedingisphaeridium sp., as well as of Leiospheres. These forms are kept in open nomenclature because they are very simple, frequently broken and difficult to attribute to already described species.