Asplenium rhizophyllum one collection on sandstone in the Shawnee Hills of Illinois. A triploid hybrid between walking fern and Tutwiler's spleenwort was accidentally produced in culture. A similar plant collected from limestone in Shepherdstown, West Virginia could have originated from the same parents, from an unreduced (diploid) gametophyte of Scott's spleenwort crossed with walking fern, or from an unreduced walking fern gametophyte crossed with ebony spleenwort. In 1813, Henry Muhlenberg listed lobed spleenwort as "Asplenium rhizophyllum" var. "pinnatifidum", although he did not provide a description distinguishing the variety from the typical species. It was described as the species "A. pinnatifidum" by Thomas
What Is and What Should Never Be What Is and What Should Never Be "What Is and What Should Never Be" is a song by English rock band Led Zeppelin. It was written by Jimmy Page and Robert Plant and was included as the second track on "Led Zeppelin II" (1969). "What is and What Should Never Be" was one of the first songs on which Page used his soon-to-become trademark Gibson Les Paul for recording. The production makes liberal use of stereo as the guitars pan back and forth between channels. Robert Plant's vocals were phased during the verses. Record producer Rick Rubin has remarked, "The