On Megaceros aenigmaticus Schust.

Abstract

The description ofMegaceros aenigmaticus Schust., briefly treated Schuster (1992), is enhanced. Two phenotypes (both lacking visible gametangia) were collected 1952: a) a weakly to moderately frilled-margined, closely pinnatifid to pinnate phase and b) an entire-margined phase, often remotely 2-3-pinnate, with very narrow ultimate pinnae, mimicking a large Riccardia mul- tifida or R. chamedryfolia. Both phases had only solitary chloroplasts of dorsal epidermal cells. It was tentatively concluded that a distinct species of Anthoceros was at hand, the single chloroplasts seeming to exclude Megaceros (to which phase a bore some resemblances). Lack ofgametangia and sporophytes precluded resolution of both generic provenance and of whether one or two intermingled taxa were at hand; the plant has remained in limbo for forty years. A preliminary account by Renzaglia and Hicks (1984) of a third phenotype appeared: c) a 9 phase with frilled thallus margins, bearing 1-4 epidermal chloroplasts per cell. The question arose: are these phases members of one species, and to what genus do they belong? In October 1987, mass collections were made order to find 6 plants and sporophytes and to try to resolve whether all these enigmatic plants belonged to one or more species. Among thousands ofplants collectedfrom several stations, afourth phenotype was found: d) vigorous ! plants with strikingly lobulate-laciniate and crispulate thallus margins, with dorsal epidermal cells with either paired or single dumbbell-shaped chloroplasts. This vari- ability-from Anthoceros-like to Megaceros-like epidermal cells-and gross variability four other criteria: a) development, or lack thereof of endogenous slime cells; b) presence or absence ofNostoc symbionts; c) number of cells delimiting the mouth of the archegonium; and d) number of cells peripheral to the ventral gametophytic stomata, are subject to in-depth investigation. It is concluded that a single, strikingly malleable species of Megaceros is at hand, differing from all well-known taxa of that primarily antipodal genus being unisexual and relying on fragmentation and re- generant-formation for its dispersal. The assumption is documented that reduction to sterile and purely 9 clonal populations, isolated limited environments western North Carolina to South Carolina, along small rills, is probably a recent (surely post-Oligocene, perhaps post-Pliocene) phenomenon. Extinction of the 6 sex is shown to be matched a number of other cases the Appalachian system.