Discovery of Papuacedrus (Cupressaceae, Libocedrinae) in Eocene Patagonia Clarifies the Southern Rainforest Enigma

WILF PETER; STEFAN LITTLE; ARI IGLESIAS

Vancouver, Canada

Congreso; Botanic Society of America annual meeting; 2008

Botanic Society of America

The early Eocene Laguna del Hunco (LH) and middle Eocene Río Pichileufú (RP) compression floras from Patagonia, Argentina are diverse, angiosperm-dominated assemblages from lowland, caldera-lake environments. They contain lineages now found in the tropical West Pacific, the Neotropics, and the Andean-Patagonian temperate rainforests. Leaf size data from our recent collections indicate annual precipitation > 1 m; Gymnostoma (LH) and drought-intolerant Podocarpaceae genera (LH, RP) also support high rainfall. However, Libocedrus prechilensis Berry 1938 is apparently affiliated with dry biomes: the name reflects similarity to an extant Patagonian endemic, Austrocedrus (then Libocedrus) chilensis, which inhabits cold steppe to northern Mediterranean climates. The holotype (RP), a vegetative branch, was the sole South American fossil reliably assigned to Libocedrinae Farjon, comprised of Austrocedrus, Libocedrus (New Zealand, New Caledonia), Papuacedrus (New Guinea and Moluccas), and Pilgerodendron (Southern Andes). New specimens referable to L. prechilensis (30 LH, 3 RP) preserve diagnostic characters not of Austrocedrus, but of Papuacedrus, including: large (to 10 mm length, juvenile type) lateral leaves in fused pairs, with convex bases, sharp-pointed, spreading free tips, darkened margins, and conspicuous resin ducts; smaller (to 0.3 mm), keeled facial leaves with comblike marginal flanges; and Florin rings in discontinuous rows. An attached seed cone (3.5 x 2.8 mm) has two decussate, unequally-sized pairs of cone scales, with a bract tip preserved near the center of an upper cone scale from which surface rugosities radiate both basally and apically. The previous fossil record of Papuacedrus is based on leaves with cuticle from the Oligocene-Miocene of Tasmania and the Miocene of New Zealand. The sole extant species, P.  papuana, is most prevalent in New Guinea cloud forests receiving up to 4 m rainfall annually. Thus, our pending new combination removes a dry-biome indicator for Eocene Patagonia and adds a link to tropical, West Pacific, montane rainforest.