Some aspects of the morphology of the rhizome of Pteris wallichiana

Abstract

Pteris wallichiana has a short thick ascending rhizome clothed by prominent, spirally arranged, swollen, fleshy, persistent, leaf bases with clusters of roots and paleae between them. A majority of the leaves are reduced, except for their swollen bases which act as storage organs. These are large fleshy ovoid organs, often 3-4×1.5-2.5 cm. in size and composed of thin-walled parenchyma cells with dense deposits of starch. A few vestigial leaves are found on the ventral side of the rhizome. All leaves are associated with an abaxial vegetative bud at its base. The prominent lenticels found on the leaf bases are formed by groups of cells of the inner cortex elongating radially and breaking open the peripheral layer of the outer cortex. The vascular cylinder of the rhizome is a solenostele with a ribbon-like medullary strand acting as a compensatory bundle to close the leaf gaps. The leaf traces are Ω-shaped solitary strands. The ground tissue of the rhizome is parenchymatous, except for a cortical intact sclerenchymatous sheath and a similar but thinner sheath surrounding the vascular cylinder. Starch deposits are absent in the cells, except in the inner cortex. In the stipe the vascular bundle is corrugated due to the protoxylem areas being raised as ridges (over 50 per stipe) and each group is associated with a mucilage-containing strand of cells on its inner surface. P. waltichiana is probably unique among ferns in having bases of reduced leaves acting as storage organs.