HYMENOPHORE DEVELOPMENT AND EVOLUTION IN LENTINUS

Morphological evolution of the Lentinus hymenophore was investigated through scanning electron microscopic observations of development in cultured sporocarps of Lentinus tigrinus, L. crinitus, L. squarrosulus, and an outgroup Polyporus arcularius. Mature L. sajor-caju sporocarps from herbarium material were also examined. The early hymenophore of P. arcularius was composed of circular pores that became radially elongate and angular as the pileus expanded. The L. tigrinus hymenophore was initially composed of irregular to subparallel ridges of hyphae that differentiated into lamellae. Subsequent growth of transverse cross-bridges resulted in a regular, subporoid structure at the base of the hymenophore. The cross-bridges, which are interpreted as homologues of the tangential walls of the P. arcularius hymenophore, were absent in L. crinitus, L. squarrosulus, and L. sajor-caju. By outgroup comparison, cross-bridges at the base of the hymenophore, moderately crowded lamellae, descending hymenophoral trama, lacerate lamella margins, and gymnocarpy are inferred to be plesiomorphic, and absence of cross-bridges. densely crowded lamellae, radiate trama, entire margins, and velangiocarpy are inferred to be derived within Lentinus. Nonterminal modifications to developmental programs and lack of correspondence between ontogenetic and phylogenetic polarity were observed. This suggests that use of ontogenetic criteria for assessing polarities and homologies of Lentinus hymenophore characters could be misleading.