Morphological and ultrastructural features in selected species of Licea (Myxomycetes)

Ultrastructural studies of selected species of Licea were made in order to elucidate relationships among species. Based on structural studies, species may be grouped as representing different stages of morphological complexity. The majority of species possess protoplasmodia and form sporangia. The two plasmodiocarpous species L. retiformis and L. variabilis possess more highly differentiated plasmodia and are an anomaly among Licea species. Processes along the margin of peridial lobes in several species of the genus are probably homologous with the capillitium in Listerella . The latter genus is morphologically and structurally very similar to species of the Licea pusilla group, but its plasmodium is still unknown. The sole species of Listerella agrees with Licea operculata in the structure of spore ornamentation, the processes consisting of densely packed granules of high electron density. This structure is quite different from that of L. pusilla and L. minima , where the processes have an internal structure of alternating layers different in electron transparency. Presence of spore-like bodies, different in size and ornamentation from normal spores, have been demonstrated in the border region between stalk and sporangium in L. operculata . This is a feature previously supposed to be restricted to Arcyria and related genera. Using X-ray analysis, calcium has been found in the peridium of several species of Licea . Since environmental factors may influence the presence or absence of calcium, caution should be taken in interpreting differences taxonomically. The similarity in elemental composition between the spores and sporangial lid in L. operculata is interesting, considering the fact that the sporangial lid of Trichia crateriformb has been demonstrated to be composed of spore-like structures.