Scolecopteris cf. alta Millay, 1982

Galtier, Jean, Ronchi, Ausonio & Broutin, Jean, 2011, Early Permian silicified floras from the Perdasdefogu Basin (SE Sardinia): comparison and bio-chronostratigraphic correlation with the floras of the Autun Basin (Massif central, France), Geodiversitas 33 (1), pp. 43-69 : 58-60

Scolecopteris cf. alta Millay, 1982

( Fig. 8D, E )

This third type of Scolecopteris is the less common but the most distinctive, with synangia circular in cross section, 0.8 mm in diameter and more than 1 mm long, generally consisting of 6 sporangia fused in their basal half (along about 600 µm) around a central column of parenchyma and fibers. Sporangia are less than 1 mm long and 200-400 µm in diameter with thin outer walls, even in their free distal region ( Fig. 8E ). The synangium pedicels are very short, broad (600 µm), parenchymatous and attached to relatively thick (400 µm) pinnules showing large mesophyll cells ( Fig. 8D ) but there is no well-differentiated palisade tissue. These fertile pinnules clearly belong to the “Altus group” of Millay (1979) and they appear more similar to the Pennsylvanian Scolecopteris alta (Watson) Millay, 1982 . The present material may also be compared to Scolecopteris globiforma from Grand-Croix and S. unita from the Lower Permian of Autun ( Millay & Galtier 1990), however, these two species differ from the Sardinian pinnules by their thick outer sporangial walls bearing hairs.

These fertile fronds of marattialeans represent one of the most important elements of the flora but the taxonomic elucidation needs additional investigation, which is out of the scope of this paper – it will be the object of a separate, detailed study.

However, we wish to emphasize that the three distinct types of Scolecopteris show differences in pinnule morphology and sporangial organization suggesting an important diversity of marattialeans at Perdasdefogu. In a palaeoecological perspective it is significant that most show rather thick pinnules (? xeromorph) which may have been efficient for water conservation in drier environments (see Barthel & Weiss 1997).

SEED PLANTS

Fragments of seed plants occur in less than 1 of 4 specimens; they correspond to stems, leaves, rachises, seeds and pieces of cortex and wood of pteridosperms or cordaiteans.

Petiole or rachis of Heterangium type ( Fig. 9J ) Such isolated rachises with up to 6 mesarch bundles (arrows, Fig. 9J ) resemble petioles of some

chyma strands conforms to the species C. crassus Renault (SAR01 AS 03); C -E, SAR01B1aB01; C, Cordaites tenuistriatus Grand’Eury, detail of transverse section of the lamina; D, Cordaites cf. crassus , detail of transverse section of the thick lamina; E, Cordaites sp., detail of a longitudinal section of the lamina showing excellent preservation of the mesophyll; F, Cordaites cf. lingulatus Grand’Eury, transverse section of lamina (SAR24B4L07); G, transverse section of three small radially symmetrical ovules showing three sutures (arrows) of the sclerotesta (SAR47A1B01); H, Cycadinocarpus augustodunensis (Brongniart) Renault , transverse section of the ovule (SAR15BT01); I, cf. Parataxospermum , transverse section of the ovule (SAR40C2T09); J, rachis of possible lyginopterid affinities showing five mesarch xylem bundles (arrows). Scale bars: A, B, G-J, 1 mm; C-F, 0.5 mm.

Pennsylvanian Heterangium illustrated by Pigg et al. (1987). Heterangium stems are known from the Lower Permian of Autun but they have not yet been found at Perdasdefogu.

Radially symmetrical ovules ( Fig. 9G )

These rare, very small ovules (2.5 to 3 mm in diameter) show a well-marked radial symmetry with evidence of three sutures of the sclerotesta (arrows, Fig. 9J ). Despite their small size, this is suggestive of affinities with medullosan pteridosperms.

Probable medullosan wood ( Fig. 10E )

A few fragments of wood, sometimes fusinized, show very broad tracheids (60-100 µm in diameter) with multiseriate (3 to 5-seriate) pitting on their radial walls and high multiseriate rays; they have characteristics of pteridosperm secondary xylem and may be attributed with some reservation to medullosans. This is supported by the occurrence of fragments of outer cortex, with parenchyma and sclerenchyma strands, of the sparganum - type which are characteristic of the stem and rachises of this group of seed ferns.

Figures

FIG. 8. — Silicified plants from the Permian of Sardinia:A, Pecop- teris sp., transverse section of one vegetative pinnule showing thick lamina with palisade and aerenchyma mesophyll.Note the hair (arrow) attached near the lower extremity (SAR15B1T02); B, Scolecopteris cf. elegans Zenker, oblique transverse section of one pinnule showing two synangia attached on the left side. Note the thick lamina similar to that of Pecopteris sp. (A) but long thin pinnule extension on the right (SAR40C01); C, Scolecopteris cf. parvifolia Millay, part of a longitudinal section of one pinnule passing through several synangia. Note the relatively thin lamina, synangia borne on a short vascularised pedicel and solid tips of sporangia (SAR56AT02); D, E, Scolecopteris cf. alta Millay; D, longitudinal section of a synangium showing the characteristic central column; E, transverse sections of synangia, the one above is through the basal part of the synangium, the other is through the distal region showing only four dehiscent sporangia (SAR01C2B02). Scale bars: 0.5 mm.

FIG. 9. — Silicified plants from the Permian of Sardinia: A, Cordaixylon sp., transverse section of a partly decorticated small stem with a solid parenchymatous pith; on the left the closely associated rachis (P) with several xylem bundles may represent a petiole of the same plant (SAR24B4L13);B, Cordaites leaves associated with Pecopteris pinnules;the broadest leaf (CC) with interfascicular scleren-

FIG. 10.— Silicified plants from the Permian of Sardinia:A-D, Da-