SUMMARY: A unique species of is described for which the binomial is proposed because of the seemingly branched character of its fructifications. This slime mould has been isolated repeatedly from samples of surface soil and decomposing leaves collected from deciduous forests in various parts of the United States. As in other members of the Acrasieae, its vegetative phase consists in the independent growth of free-living myxamoebae which feed upon bacterial cells, and its fruiting phase is characterized by the inflowing of these cells to form multicellular organizations preparatory to fructification. differs from previously known species of the genus, particularly for its formation of cell aggregates which give rise to varying numbers of long, thin migrating pseudo-plasmodia, and for the potential capacity of each of these to form subsequently a small coremiform fructification consisting of multiple sorocarps. Whereas some simple sorocarps are regularly produced, fructifications under optimal conditions typically consist of from two to ten adherent sorocarps. In such coremiform structures, the sorophores of individual sorocarps, although clearly distinguishable microscopically, are tightly appressed for approximately three-quarters of their length, at which level they diverge sharply and at their apices bear globose spore heads, or sori. The spores are elliptical to reniform as in most species, but germinate by the swelling and dissolution of the spore wall in a median plane rather than by longitudinal splitting.


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