Sigillaria is another important arborescent Carboniferous-Permian lycopsid, which did not branch profusely and was

figure 9.83 Suggested reconstruction of Sigillaria tree (Pennsylvanian). (Courtesy D. A. Eggert.)
Sigillaria Tree
figure 9.84 Sigillaria mammillaris, stem surface with leaf bases (Pennsylvanian). Bar = 2 cm. (Courtesy BSPG.)

not as large as the lepidodendrids. Although some specimens have been reported to be >30m tall (FIG. 9.83), it is probable that most sigillarians were <20 m tall. The absence of extensive branching and the structure of the leaf bases are the principal features that distinguish Sigillaria from other arborescent lycopsids. Sigillarian leaf bases are typically hexagonal in outline (FIG. 9.84), although some may be elliptical. Although they are helically arranged, they often appear to be aligned in vertical rows. The actual leaf scars are generally elliptical (FIG. 9.85), with a central leaf-trace scar (vascular-bundle scar) flanked by two large parichnos scars. The vascular bundle is v-shaped and may separate into two strands. A ligule scar is present above the leaf scar.

Leaf Bases

Subgenera of Sigillaria have been established to encompass the various configurations and arrangements of the leaf bases on the surface of the stems. Sigillaria subg. Eusigillaria includes forms with ribbed stem surfaces, and these have been divided into two sections. In the section Rhytidolepis , leaf bases and ribs are separated and the furrows between adjacent ribs are straight or nearly so. In the section Favularia, leaf bases and ribs are close together and the furrows have a zigzag configuration. Forms included in Sigillaria subg. Subsigillaria lack ribs. There are also two sections within this subgenus: Leiodermaria has widely

Was this article helpful?

0 0

Post a comment