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Despite the extraordinary significance leaves have for life on Earth, their origin and development remain vigorously debated. More than a century of paleobotanical, morphological, and phylogenetic research has still not resolved fundamental questions about leaves. Developmental genetic data are sparse in ferns, and comparative studies of lycophytes and seed plants have reached opposing conclusions on the conservation of a leaf developmental program. We performed phylogenetic and expression analyses of a leaf developmental regulator (Class III HD-Zip genes; C3HDZs) spanning lycophytes and ferns. We show that a duplication and neofunctionalization of C3HDZs probably occurred in the ancestor of euphyllophytes, and that there is a common leaf developmental mechanism conserved between ferns and seed plants. We show C3HDZ expression in lycophyte and fern sporangia and show that C3HDZs have conserved expression patterns during initiation of lateral primordia (leaves or sporangia). This expression is maintained throughout sporangium development in lycophytes and ferns and indicates an ancestral role of C3HDZs in sporangium development. We hypothesize that there is a deep homology of all leaves and that a sporangium-specific developmental program was coopted independently for the development of lycophyte and euphyllophyte leaves. This provides molecular genetic support for a paradigm shift in theories of lycophyte leaf evolution.

Holden Caulfield, the beat writers, Elvis Presley, Chuck Berry, and James Dean—these and other avatars of youthful rebellion were much more than entertainment. As Leerom Medovoi shows, they were often embraced and hotly debated at the dawn of the Cold War era because they stood for dissent and defiance at a time when the ideological production of the United States as leader of the \"free world\" required emancipatory figures who could represent America's geopolitical claims. Medovoi argues that the \"bad boy\" became a guarantor of the country's anti-authoritarian, democratic self-image: a kindred spirit to the freedom-seeking nations of the rapidly decolonizing third world and a counterpoint to the repressive conformity attributed to both the Soviet Union abroad and America's burgeoning suburbs at home. Alongside the young rebel, the contemporary concept of identity emerged in the 1950s. It was in that decade that \"identity\" was first used to define collective selves in the politicized manner that is recognizable today: in terms such as \"national identity\" and \"racial identity.\" Medovoi traces the rapid absorption of identity themes across many facets of postwar American culture, including beat literature, the young adult novel, the Hollywood teen film, early rock 'n' roll, black drama, and \"bad girl\" narratives. He demonstrates that youth culture especially began to exhibit telltale motifs of teen, racial, sexual, gender, and generational revolt that would burst into political prominence during the ensuing decades, bequeathing to the progressive wing of contemporary American political culture a potent but ambiguous legacy of identity politics.