SEM Studies on Vessels in Ferns. 18. Montane Cheilanthoid Ferns (Pteridaceae) of North America

摘要

Xylem of roots and rhizomes of five species of four genera of tribe Cheilantheae (Pteridaceae; recently recognized by some as a segregate family, Cheilanthaceae) has been studied by means of scanning electron microscopy (SEM). All of these species occur in habitats (cliffs, talus) of mountains of North America that are seasonally dry in summer and cold in winter. The vessels prove diverse, indicating that different perforation plate modifications are represented in the cheilanthoid ferns of these habitats, rather than different degrees of the same kind of modification. The modifications include wide perforations alternating with narrow perforations (especially prominent in Bommeria); discontinuous perforation plates (Cheilanthes, Pellaea); and narrow, slitlike perforations (Cheilanthes). The discontinuous perforation plates are newly reported for ferns. The exceptionally prominent perforations of Bommeria vessels may be correlated with greater laminar surface and higher transpiration during wet periods in that genus; the other genera have small laminae with probable low transpiration rates even during moist periods.