Geographic and environmental factors controlling life history and morphology inPrasiola stipitata Suhr

Summary

The vertical distribution of meiotic and non-meiotic plants, of the spore-formation types, of the presence of filamentous stage and, in some cases, of thallus sizes was analyzed in 57 populations ofPrasiola stipitata, collected on both sides of the Atlantic.

A vertical zonation exists within the limits of thePrasiola stipitata belt. In the higher levels there are less or no meiotic plants, the thallus size is smaller and the filamentous (Rosenvingiella-) stage may be present. In the lower levels, the ratio of meiotic plants as well as the size of the thallus increases and the filamentous stage is absent. The distribution of marginal and variegated sporophytes does not present a clear pattern, though the marginal type often seems to prevail in the higher levels and the variegated type in the lower. Seasonality is apparent in the decrease of both thallus size and of the ratio of meiotic plants towards the end of the growth season.

On the eastern shores of the Atlantic growth is perennial and meiotic plants are infrequent or absent from about 55° latitude northwards. South of this line growth is seasonal and meiotic plants are abundant. On the western shores of the Atlantic growth is perennial and gametophytes are absent from 44° latitude northwards.