Palaeostachya, C.E.Weiss, 1876

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 : 52

Palaeostachya sp. ( Fig. 5 A-E)

Small cones 2-4 mm long and up to 10 mm in diameter are relatively common elements of the assemblage. They show whorls of 24 or 28 separate sterile bracts at each node, one half of the bract subtend the 12 or 14 axillary sporangiophores ( Fig. 5B ). In cross section the cone axis is broadly circular (3-5 mm in diameter) with a pith cavity and 12 or 14 primary xylem bundles with a carinal canal ( Fig. 5C ). There is a discontinuous narrow zone of secondary xylem and, at the node level, lacunae are present in the cortex of the cone axis, immediately outside the secondary xylem. In most specimens the bracts are broken at their point of attachment to the cone axis ( Fig. 5A [B]); they extend perpendicularly outwards for a short distance before ascending vertically for about 10 mm, i.e. a little more than two nodes ( Fig. 5A ); this is confirmed by transverse sections showing two or three whorls of bracts ( Fig. 5A [B]). The measured length of the internodes is 3.7 to 4 mm. Individual bracts show a maximum tangential diameter (1 mm) in the ascending lamina. The sporangiophore stalks arise obliquely from the base of the bracts ( Fig. 5A [ST]), a characteristic feature of Palaeostachya cones. Sporangiophores are borne by two contiguous (fertile) bracts alternating with two sterile ones. The stalks are narrow (0.3 × 0.4 mm in diameter), losangic in transverse section with a sclerenchym with a sclerenchymatous black cortex efficient for mechanical support of the sporangia (arrows on Fig. 5D ). The sporangiophores are peltate ( Fig. 5C [P]), each bearing 4 sporangia. Nearly all the sporangia ( Fig. 5 A-C [S]) are dehiscent and distorted, however, we can estimate their length to 2 mm and their diameter to 1 mm. The peltate sporangiophore head ( Fig. 5C [P]) is about 2 mm broad and parenchymatous tissue extends at the base of each sporangium. Spores are rarely preserved, spherical, about 100 µm in diameter (arrows, Fig. 5E ).

In their general organization these cones are similar to those of Palaeostachya andrewsii ( Baxter, 1954) from Pennsylvanian coal balls of Iowa based on an exceptionally preserved specimen allowing to recognize features not completely available in our material; in addition, the spores of the American cone are larger. A detailed study is necessary to decide of the taxonomic attribution of the present specimens which can also be compared to Palaeostachya (Volkmannia) gracilis cones described by Renault (1876; 1896) from the Lower Permian of Autun. One of us (JG) recently re-investigated Renault’s material and recognized strong similarities, but the cones from Autun correspond to several taxa, generally of larger size, with the exception of one specimen described as “ Volkmannia ” sp. (Renault 1896).

Figures

FIG. 5. — Silicified plants from the Permian of Sardinia: A-E, Palaeostachya sp.: A, longitudinal section of the cone showing the central axis with pith cavity (A) and three nodes with the attachment of bracts (B) and sporangiophore stalks (ST) arising obliquely. The bracts are often displaced at their base (B with two arrows) whilst their distal part is ascending vertically (see on the left) (S), de-