SPOROCARP ONTOGENY IN PANUS (BASIDIOMYCOTINA) - EVOLUTION AND CLASSIFICATION

Ontogenies of cultured Panus conchatus, P. rudis, and P. fulvus sporoc arps were observed macroscopically and with scanning electron microsco py. Hymenophore differentiation in Panus involves periclinal growth of context hyphae below a closed surface palisade of hymenial elements, resulting in a cantharelloid appearance and radiate trama. This patter n is qualitatively different from that in Lentinus s. str., which sugg ests that lamellae of Panus and Lentinus are not homologous. Panus con chatus and P. rudis sporocarps have short stipes, develop directly fro m the mycelium, and mature in 5-10 d. Panus fulvus sporocarps have an elongate stipe, develop from a pseudosclerotium, and mature in about 3 wk, the first approximately 15 d of which involve apical elongation o f a stipelike primordium that is able to dedifferentiate and regenerat e cut apices. Panus conchatus and P. rudis sporocarps lacked regenerat ion ability. Panus conchatus sporocarps developed an ephemeral partial veil that was obliterated during sporocarp expansion. Outgroup compar ison suggests that evolutionary changes in developmental programs in P anus have included: 1) delay in offset of primordium growth, with a co rresponding increase in primordium size and time to maturation (hyperm orphosis); 2) insertion of the pseudosclerotial stage in ontogeny; 3) gain of ability for dedifferentiation and regeneration; and 4) nonterm inal gain or loss of veil tissue.