Sporocarp ontogeny in Panus (Basidiomycotina): evolution and classification

Ontogenies of cultured Panus conchatus, P. rudis, and P. fulvus sporocarps were observed macroscopically and with scanning electron microscopy. 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 pattern is qualitatively different from that in Lentinus s. str., which suggests that lamellae of Panus and Lentinus are not homologous. Panus conchatus and P. rudis sporocarps have short stipes, develop directly from 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 of a stipelike primordium that is able to dedifferentiate and regenerate cut apices. Panus conchatus and P. rudis sporocarps lacked regeneration ability. Panus conchatus sporocarps developed an ephemeral partial veil that was obliterated during sporocarp expansion. Outgroup comparison suggests that evolutionary changes in developmental programs in Panus have included: 1) delay in offset of primordium growth, with a corresponding increase in primordium size and time to maturation (hypermorphosis); 2) insertion of the pseudosclerotial stage in ontogeny; 3) gain of ability for dedifferentiation and regeneration; and 4) nonterminal gain or loss of veil tissue.