THE FOSSIL MONOCOT LIMNOBIOPHYLLUM SCUTATUM - RESOLVING THE PHYLOGENYOF LEMNACEAE

More than 200 specimens of Limnobiophyllum scutatum (Dawson) Krassilov have been recovered from lacustrine claystones in the Paleocene Paska poo Formation near Red Deer, Alberta. The plant was a floating, aquati c angiosperm with helically arranged, ovate leaves attached in small r osettes. Rosettes are interconnected by stolons and bear simple advent itious roots as well as larger branching roots that appear to have vas cular tissue. Leaves are pubescent, aerenchymatous, with 12-14 campylo dromous primary veins that curve toward the apex, joining a fimbrial v ein, often an apical notch. Staminate flowers with two, four-loculate stamens, are borne in the axils of second leaves. Anthers contain mono porate, globose, echinate pollen, 20-25 mu m in diameter. The pollen w all is 0.8 mu m thick, with a homogeneous foot layer, granular to slig htly columellate infratectal layer and an echinate tectum. Pollen most closely resembles the sporae dispersae genus Pandaniidites Elsik. The completeness of L. scutatum has allowed for its inclusion in a numeri cal cladistic analysis to resolve relationships among taxa of the Lemn aceae, Pistia, and selected genera of Araceae. Results of the analysis indicate that the Lemnaceae plus Pistia form a monophyletic group wit hin the Araceae.