The Jebel Koumine is located in central Tunisia (Fig. 1), less than 10 km south of the city of Sbitla and about 30 km north-west of Jebel Kebar (the type locality of the Kebar Formation). In this area, an anticline oriented East to West allows Aptian to Cenomanian rocks to crop out, directly covered by Cenozoic strata. The Kebar Formation in Jebel Koumine crops out exclusively on the northern flank of the structure (Fig. 2A), with a total thickness of 230 m and lying unconformably on the uppermost member of the dolomitic Orbata Formation, Lower Aptian in age (Masse, 1984 and M’Rabet, 1981). This superposition represents a major regional unconformity, documented throughout Central Tunisia (Ben Youssef, 1999, Masse, 1984 and M’Rabet, 1981). The Kebar Formation is directly overlain by transgressive marine marls and limestones of the Zebbag Formation, Upper Albian in age (Stoliskaia dispar ammonite biozone, according to Ben Youssef, 1999). This stratigraphical context frames the Kebar Formation between the Upper Aptian-Upper Albian interval. Recently, Trabelsi et al. (2010) attributed this formation more precisely to the Lower Albian, based on a charophyte assemblage. This age was also confirmed by a rich assemblage of ostracods (Trabelsi et al., 2011; Trabelsi and Colin, work in progress).

The vertical change in the lithofacies and stacking-pattern in the main section called DED, located near the path of “Draa El Deba” on the northern flank of Jebel Koumine (Fig. 2A), allows us to subdivide the Kebar Formation into four lithostratigraphic units that represent a fluvio-lacustrine environment (Fig. 2B). Level KM75 from the DED section is a lacustrine limestone, at the top of unit 1 of the Kebar Formation (Fig. 2B), which provided a large amount of well-preserved fructifications (gyrogonites and utricles) of charophytes. Moreover, this bed provided a new species of the genus Echinochara, associated with Sphaerochara verticillata var. kebariensis Trabelsi 2010, Clavator harrisii var. zavialensis (Grambast-Fessard, 1980) Martín-Closas, 1996 and Atopochara trivolvis var. trivolvis Peck, 1938 (Fig. 3B–D). The assemblage formed by the three latter species has recently been described in the Lower Albian of Tunisia by Trabelsi et al. (2010).

Samples taken in the consolidated limestone bed KM75 were treated using acetolysis, breaking down the rock by preliminary attack with acetic acid. The efficiency of this method, first advocated by Nötzold (1965) and already applied by Trabelsi et al. (2010), has recently been demonstrated by Rodriguez et al. (2011). It consists in taking the sample of calcareous rock, perfectly dried and mechanically comminuted in fragments about 1–3 mm across, and adding similar amounts of anhydrous acetic acid and anhydrous copper sulfate (acid attacks in an exothermic reaction). After neutralization of the milieu by ammonia, the residue is treated with ultra-sound, then washed and rinsed. The studied material is stored at the Service of Paleontology and Sedimentology of the National Office of Mines of Tunisia under reference SPSONMT Trab., J. Koum. 0018–0035.

Division CHAROPHYTA Migula, 1897

Class CHAROPHYCEAE Smith, 1938

Order CHARALES Lindley, 1836

Family CLAVATORACEAE Pia, 1927

Subfamily ATOPOCHAROIDAE Grambast, 1968 emend. Martín-Closas, 1989 ex Schudack, 1993

Genus Echinochara Peck, 1957 emend. Schudack, 1993

Echinochara triplicata, Trabelsi et Martín-Closas nov. sp.

Fig. 3A.

Material: One well-preserved specimen, showing a symmetry unit of an Echinochara utricle and up to 10 more specimens, poorly preserved but with a similar structure.

Diagnosis: Utricle of Echinochara with the external whorl formed by three radially-symmetrical units, each formed by 21 elongated and non-branched vertical bract cells, directly connected to the utricle base, where the scar of the attachment cell can be observed.

Derivation of name: From the Latin adjective triplicata, meaning threefold. The new species in fact represents a triplication of the number of cells of the utricle of Echinochara peckii var. lazarii Martín-Closas, 2000, from which it is hypothesized to derive.

Holotype: Specimen num. SPSONMT Trab., J. Koum. 0025 (Fig. 3A), stored at the Service of Paleontology and Sedimentology of the National Office of the Mines of Tunisia (charophyte collection from J. Koumine, 2011).

Paratypes: Specimens num. SPSONMT Trab., J. Koum. 0026–0031, stored at the Service of Paleontology and Sedimentology of the National Office of the Mines of Tunisia (charophyte collection from J. Koumine, 2011).

Type locality: Section DED of the Kebar Formation located in the South East of Draa el Deba in the northern flank of Jebel Koumine. Coordinates: N 35° 70′; E 90 90′.

Type-layer: Limestone level KM75 of section DED, 60 metres from the base and 10 metres from the top of the basal unit (U1) of the Kebar Formation in Jebel Koumine; Lower Albian in age.

Description: Utricles of the new species were found preserved as calcite plates with an arrangement reminiscent of the external plates of the Echinochara peckii utricle (Fig. 3). These plates are about 600 μm wide and 850 μm long. On one side of the plate there are 21 vertical furrows, 310 to 540 μm long and 10 to 15 μm wide, converging to the base where they are attached. These 21 furrows are attributed to the bract cells of one symmetrical unit of the external whorl of an Echinochara Peck, 1957 utricle, as described by Schudack (1993). The bract cells are grouped in three sets of seven cells each (Fig. 4). The medial set bears thinner and longer bract cells, running linearly throughout the plate from the base to the top. It is embraced on each side by another set of seven cells each, which are slightly convergent to the base but shorter, wider and progressively more curved inwards towards the top. The basal part of the plate shows a rounded attachment scar, about 130 μm across with a prominent peripheral rim, which was attributed to the scar of the abaxial internal bract, sensu Schudack (1993). This scar is the only available proof that the internal series of bracts still existed in Echinochara triplicata nov.sp., because on the opposite side of the calcite plate the surface is irregular and unstructured. In consequence, no marks of the gyrogonite are available in the material studied.

Remarks: The organization of the utricle cells in each symmetry unit of the new species recalls the fan-like structure of the utricle wall of Echinochara peckii var. lazarii Martín-Closas, 2000. As in this morphotype, in the E. peckii triplicata nov. sp., all the cells depart directly from the attachment scar, and are not arranged in two successive trifurcations as in the case of Echinochara peckii var. peckii. However, unlike E. peckii var. lazarii, the new species bears symmetry units, each formed by 21 cells instead of seven.

Distribution: Echinochara triplicata, from the Lower Albian of Tunisia, is the youngest species of the genus Echinochara and is also its first African record. Genus Echinochara Peck, 1957 shows a rather disjointed distribution in both time and space. The oldest record of the genus is represented by Echinochara peckii peckii (Mädler, 1952) which occurs in the Oxfordian of Switzerland (Mojon, 1989) and in the Kimmeridgian of the United States and Germany (Mädler, 1952, Schudack, 1993 and Schudack et al., 1998). A second species, Echinochara spinosa Peck, 1957, was also described from the Kimmeridgian of the Morrison Fm (United States). Additionally, Mojon and Mouchet (1992) claimed that Echinochara-like vegetative remains found in thin sections from the Lower Kimmeridgian of the Jura Mountains (Switzerland) belonged to E. peckii, but insufficient evidence was provided to characterize the utricle on which the species is based. There is a significant gap in the record of the genus Echinochara from the Tithonian to the Hauterivian. After this gap, a later morphotype of this species (E. peckii var. lazarii) occurs in the Lower Barremian of the Iberian Peninsula (Martín-Closas, 2000) and in the Upper Barremian and Lower Aptian of the Subalpine Chains, France (Martín-Closas et al., 2009).

The genus Echinochara (subfamily Atopocharoidae) is currently represented by the two taxa Echinochara spinosa Peck, 1957 and Echinochara peckii (Mädler, 1952) nov. comb. Grambast, 1956 emend. Schudack, 1993). The genus as a whole was considered by Martín-Closas, 1989 and Martín-Closas, 1996 a paraphyletic ancestral stock from which the remaining Atopocharoidae were derived. Echinochara spinosa was interpreted by Martín-Closas (1996) as the ancestral form of the genus on the basis of its utricle, formed by six trifurcated bract cells in the internal whorl, and six profusely trifurcated bract cells in the external whorl. Echinochara peckii was seen as a more derived utricle structure, with only three trifurcated bract cells in the internal whorl. The external whorl, described by Schudack (1993), showed a completely new structure, with three symmetrical plates formed by the fusion of bracts, trifurcated twice. The precise phylogenetic relationships between the two species are difficult to ascertain given the present knowledge of their utricle structure.

The new species Echinochara triplicata shows clear affinities with Echinochara peckii, particularly with the youngest morphotype of this species, E. peckii var. lazarii Martín-Closas, 2000. Like this variety, E. triplicata has the utricle formed by three symmetrical plates with the cells directly departing from the attachment scar, instead of being organized in two successive trifurcations as in the case of the nominal variety, Echinochara peckii var. peckii (Mädler, 1952). However, the new species bears symmetry units formed by three times as many bracts as in E. peckii var. lazarii. Multiplication of parts of the same structure in closely related species is known in other clavatoraceans. For example, according to Martín-Closas (1996), Clavator brachycerus (Grambast, 1962) emend. Martín-Closas, 1996 represents a triplication of the same utricle bract structure as its presumed ancestor Clavator ampullaceus (Grambast and Lorch, 1968) Martín-Closas, 1996. Again, Clavator ultimus (Grambast, 1971) Martín-Closas, 1996 has 50% more utricle bracts than its ancestor, C. brachycerus, but there is no change in the original structure. Martín-Closas (1996) suggested that such multiplications could be the result of processes of polyploidy.

According to Martín-Closas (1996), the evolutionary lineage Globator Grambast, 1966 was also derived from Echinochara peckii; however, this branch separated much earlier than Echinochara triplicata, at least in the Tithonian. Also, it represented a more significant change in the utricle structure, because Globator completely lacks the internal whorl of Echinochara's utricle, although it retains one of the two successive trifurcations of the external utricule layer of Echinochara peckii var. peckii.

Echinochara triplicata nov. sp. represents the third known species within the genus Echinochara Peck, 1957. Phylogenetic relationships of the new species are proposed with E. peckii var. lazarii from the Lower Barremian to Lower Aptian of Europe, on the basis of the non-ramified structure of the utricle's external whorl (Fig. 5). However, compared with its presumed ancestor, the new species displays three times the original number of cells per symmetry unit.

Echinochara triplicata nov. sp. can be considered a new tool for biostratigraphic studies in the non-marine Upper Jurassic-Lower Cretaceous of the Peritethyan Realm. It is especially important because it provides a new taxon for better characterization of the Upper Aptian-Lower Albian biozone of the charophyte biozonation (Clavator grovesii lusitanicus biozone) as defined by Riveline et al. (1996), which is poorer in biostratigraphically useful species than other Lower Cretaceous charophyte biozones.

The new species represents the first record of the genus Echinochara Peck, 1957 from Africa and the first in the world from the Albian. Its occurrence in the Albian shows that the genus attained a very long chronostratigraphic range, comparable to, or even longer than, the range of the closely related genera Globator Grambast, 1966, which extended between the Tithonian and the Lower Aptian, or Atopochara Peck, 1938, which extended between the Berriasian and the Maastrichtian (only between the Berriasian and the Cenomanian in the Peritethyan realm). In addition, the total biogeographic range reached during the history of the genus Echinochara was very wide, subcosmopolitan in the Northern Hemisphere (North America, Europe and Africa).