LIMNOBIOPHYLLUM KRASSILOV - A FOSSIL LINK BETWEEN THE ARACEAE AND THELEMNACEAE

Limnobiophyllum Krassilov includes fossil free-floating stoloniferous plants each with one or two sessile suborbicular to reniform leaves of different size as well as numerous simple and one or two longerbranch ed roots on a reduced main stem. The venation consists of campylodromo us curved primaries, up to 14 in number, among which irregular reticul ate veins of higher orders can be preserved. There are no signs of lat eral pouches characteristic of the Lemnaceae. However, aerenchyma and pigment cells are well developed in Limnobiophyllum, Two species are r ecognized - Limnobiophyllum scutatum (Dawson) Krassilov (latest Cretac eous to Oligocene of western North America and Palaeocene of East Asia ) and Limnobiophyllum expansum (Heer) Kvacek, comb. n. (Miocene of Eur ope). Turion-like bodies are associated with L. scutatum. No fruits ha ve been found in connection, but numerous isolated ribbed seeds are as sociated with L. expansum. They resemble some Araceae and also Lemna L . and Spirodela Schleid. Such seeds are known as Lemnospermum Nikitin from the Tertiary of Eurasia. Limnobiophyllum resembles in some respec ts Spirodela, but it is larger and the roots and the habit are more li ke young plants of Pistia L. (Araceae). It differs from Hydromystria M ey. (i.e. Limnobium Rich.) by venation, root system and habit; the Lem naceae, although similar, differ by lateral pouches of leafy fronds an d the lack of branched roots and higher-order veins. Limnobiophyllum i s considered as an extinct link related to Pistia (Araceae),from which Spirodela (Lemnaceae) may have evolved by reduction.