Ontogeny of Ctenitis melanosticta (Kunze) Copel. and Diplazium expansumWilld. (Dryopteridaceae) fronds with emphasis on the circumendodermal sheath

The ontogeny of Ctenitis melanosticta ( Kunze ) Copel. and Diplazium expansum Willd. fronds was studied with the main goals to determine if continuous and discontinuous sheaths (bands in tranverse section) have the same origin in parenchyma cells. Frond ontogeny was followed from the crozier (fiddlehead) to the mature frond. Differentiation of the sheath begins during the crozier stage a few centimeters from the base of the stipe. As seen in transverse section, band differentiation occurs in the innermost parenchyma cells of the ground tissue, which surrounds the vascular strands of each vascular bundle of a multiple leaf trace. Based on its position and origin, it is named circumendodermal band (sheath in three dimensions) and the discontinuous form is designated “perforated sheath”. The circumendodermal band and the endodermis arise from parenchyma cells. Both the continuous circumendodermal band in C. melanosticta and the discontinuous circumendodermal band in D. expansum differentiate from ground parenchyma cells surrounding each vascular bundle. In the lamina of C. melanosticta , the circumendodermal band differentiates when frond is fertile and in the lamina of D. expansum , it never differentiates. The circumendodermal band traits are not related to plant size, but to number of vascular strands. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)