Salviniaceae

Abstract

Free-floating aquatic plants with horizontal protostelic stems. Roots lacking. Leaves in groups of three along the length of the stem, each group consisting of two dorsal floating, green, simple, entire leaves and one ventral, strongly branched, submerged leaf. Floating leaves nearly sessile or short-stalked, usually ovate to cordate, with costa and anastomosing lateral veins without free included veinlets. Upper surface with special water-repellent hairs. Submerged leaf usually with a well-defined petiole. Shoots, submerged leaves, and lower parts of floating leaves bearing uniseriate, multi-cellular, apiculate hairs. Spore-producing organs borne on the submerged leaves, consisting of sori surrounded by a globose indusium (“sporocarp”). One or a few basal sporocarps containing up to about 40 megasporangia, the other (more numerous) sporocarps containing numerous microsporangia. Sporangia without dehiscence mechanism. Microsporangia containing either 64 or 32 trilete spores, these all together enclosed in a hardened, alveolar mass: the massula. Megasporangium originally containing 32 spores, only one of which develops into a mature trilete spore. Spores spheroidal; megaspores shallowly rugose to nearly plain and perforate; microspores shallowly rugose to rugulose. Microprothallium reduced, only a few cells long, with two reduced antheridia. Megaprothallium free-floating, about 0.5–1 mm long, consisting of more or less heart-shaped tissue of a few cell layers, connected with the megasporangium, normally with only a few archegonia.