Heterosporous ferns from Patagonia: the case of Azolla

Abstract

We describe megaspore apparatuses and microspore massulae of Azolla coloniensis sp. nov., a heterosporous water fern of the family Salviniaceae. The megaspore apparatus is composed of the megaspore body and three tiers of floats covered by a dense filosum, while its wall consists of an exine and a two-layered perine, with a spongy endoperine and large, clavate exoperine. Microspore massulae are variable in size and shape and bear aseptate glochidia with anchor-shaped tips. The new species increases the scarce record of Salviniaceae megaspores in the Southern Hemisphere and significantly extends our knowledge of the variability of morphological characters of the genus. Fossils indicate a freshwater depositionalenvironment and are interpreted as being preserved in situ due to their excellent preservation and the frequent attachment of microspore massulae to megaspores. This contribution supports the hypotheses of the rapid geographic dispersal anddiversification of the genus, in both hemispheres, during the Late Cretaceous.