A Ranunculalean liana stem from the Cretaceous of British COlumbia Canada: Atli morinii gen. et sp. nov.
Smith S Y; Little S A; Cooper R L; Burnham R J; Stockey R A
International Journal of Plant Sciences
Premise of research. The lianoid habit is found in 125 extant plant families and is most diverse and \r\nabundant in structurally complex forests such as tropical forests. A stem with lianoid anatomy is described \r\nfrom Cretaceous sediments of Hornby Island British Columbia. \r\nMethodology. The stem segment 2.5 cm in diameter and 2.8 cm long was studied using the cellulose \r\nacetate peel technique and SEM. Anatomy was documented and compared to fossil and modern taxa. \r\nPivotal results. The stem lacks distinct growth increments and the ?brous wood is dissected by large \r\n(110 cells wide) rays. Wood is diffuse porous with mostly solitary vessels rarely in tangential multiples (2– \r\n4). Vessel elements have a mean tangential diameter of 198 mm and mean length of 527 mm bearing medium \r\nto large crowded elliptical to ?at-elliptical alternate pits. Axial parenchyma is diffuse and vessels are sur- \r\nrounded by vasicentric tracheids with alternate bordered pitting. Rays are homocellular and 12 cm tall. Phloem \r\nrays are dilated protruding into the xylem rays; thick-walled ray cells contain prismatic crystals. Periderm is \r\ncomposed of thin-walled cells interspersed with sclerotic nests. Wood anatomy of the fossil shows the most \r\nsimilarity to that of lianas in the Menispermaceae Lardizabalaceae and Ranunculaceae. \r\nConclusions. The Hornby Island stem represents a new taxon Atli morinii gen. et sp. nov. (Ranunculales). \r\nThis liana specimen expands our knowledge of Cretaceous biodiversity and points to the presence of structurally \r\ncomplex forests on Hornby Island in the Campanian. Anatomy of Atli and other Cretaceous liana stems \r\ncombines characteristics of several families in Ranunculales documenting past anatomical diversity and pos- \r\nsible stem lineage mosaicism. The most diverse lianoid lineages currently known from the Cretaceous and \r\nPaleogene are early-divergent eudicots particularly Ranunculales and Vitales that account for more than 50% \r\nof described lianoid species during this key time period of angiosperm diversi?cation.