Final answer:
A clade is a monophyletic group consisting of an ancestor and all of its descendants and is identified through cladistics using a phylogenetic tree. It represents organisms' evolutionary relationships rather than other characteristics such as appearance or geographic distribution.
Step-by-step explanation:
A clade is a monophyletic group of organisms that includes an ancestor and all of its descendants. This concept is a fundamental aspect of cladistics, which is a method used to organize organisms based on their evolutionary relationships. Clades are determined by branching points on a phylogenetic tree where a single lineage splits into distinct new ones. Each clade can contain multiple groups or a single group, but importantly, all organisms in the clade trace back to a single ancestral point, hence being monophyletic. Cladograms, a visual representation of the relationships within a clade, utilize both morphological and genetic evidence to map out the evolutionary pathways of life.
When considering the options provided in the question, option B states: A clade is a nested grouping of organisms, clade within clade, that organizes organisms by ever more distant common ancestors, which accurately defines a clade. This concept highlights that evolutionary relationships are more accurate indicators for organizing biodiversity than appearance, geographic distribution, or order of discovery.