HYMENOPHORE DEVELOPMENT AND EVOLUTION IN LENTINUS

Morphological evolution of the Lentinus hymenophore was investigated t hrough scanning electron microscopic observations of development in cu ltured 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 elong ate and angular as the pileus expanded. The L. tigrinus hymenophore wa s initially composed of irregular to subparallel ridges of hyphae that differentiated into lamellae. Subsequent growth of transverse cross-b ridges resulted in a regular, subporoid structure at the base of the h ymenophore. 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 compariso n, cross-bridges at the base of the hymenophore, moderately crowded la mellae, descending hymenophoral trama, lacerate lamella margins, and g ymnocarpy are inferred to be plesiomorphic, and absence of cross-bridg es. densely crowded lamellae, radiate trama, entire margins, and velan giocarpy are inferred to be derived within Lentinus. Nonterminal modif ications to developmental programs and lack of correspondence between ontogenetic and phylogenetic polarity were observed. This suggests tha t use of ontogenetic criteria for assessing polarities and homologies of Lentinus hymenophore characters could be misleading.