Abstract


A new thallose hepatic with characters intermediate between those of the Sphaerocarpineae (sensu Müller) and the section Caudiciformes of the Marchantiineae has been discovered on saltpans in north-western Victoria. The female thallus bears a single spherical involucre which has air chambers and specialized pores and contains a single sporophyte. The male plants have not been found. Details are given of the structure and mode of development of the involucre, air chambers, and pores, the early embryogeny of the sporophyte, spore germination, and the development of the thallus. The systematic position of the new plant (Monocarpus sphaerocarpus) is discussed and the literature on the relationship between the Sphaerocarpineae and other thallose hepatics is reviewed. The characters of Monocarpus are shown to support the view that phaerocarpus and allied genera should be placed within the Marchantiales rather than with the Jungermanniales. It is proposed to raise a new suborder of the Marchantiales, Monocarpineae, for the single genus, Monocarpus. Certain problems of morphogenesis are raised and it is suggested that the enciosure of more than one archegonium in an involucre is conducive to the inhibition of development of more than one sporophyte within the involucre. It is also suggested that growth substances released during meiosis in the sporangium control the post-fertilization growth of the thallus and involucre.