An early Paleocene flower related to Resedaceae (Brassicales) bearing in situ pollen and cuticle from Patagonia, Argentina.

ARI IGLESIAS; STEFAN LITTLE; WILF PETER

Bonn, Germany

Congreso; International Organization of Paleobotany Conference; 2008

International Organization of Paleobotany

Early Paleocene macrofloras from Patagonia, Argentina are proving to be considerablyricher than comparable Northern Hemisphere fossil floras. From more than 3500specimens recently collected from two Paleocene formations in central Patagonia (~ 62Ma), our studies confirmed 43 new species of angiosperm leaves. Nearly 50 specimensare reproductive structures, including flowers, seeds, fruits and cones, and 36 of these areflowers preserved as compressions, representing at least six new species. Here, weintroduce a new element found at three Patagonian localities separated by 35 km totaldistance. The flowers are exceptionally preserved, and they encompass severaldevelopmental stages; using fluorescence and scanning electron microscopy, we wereable to recognize many characters including those of in situ pollen and cuticle. Theflowers are small (10 mm diam., 8 mm length), radial to slightly asymmetrical, andbisexual. The perianth is composed of a distinct valvate calyx formed by 8-9 sepals, and acorolla formed by isomerous (8-9) deeply fringed, alternate petals, each with two-threemajor lobes. The well-developed hypanthium is not free and bears an intrastaminal ringof trichomes. The gynoecium is superior, and carpels are completely covered by longacicular trichomes, but six large free styles are present at anthesis. Where preserved, theellipsoidal, bithecate anthers are large (1 mm long) and have a persistent fluorescingendothelium. Pollen grains, found within anthers and among the dense carpel trichomes,are small (14 μm polar length), prolate, and tricolporate with tectate perforatesculpturing. This combination of floral characters is known only in two families:Resedaceae (Brassicales) and Rhizophoraceae (Malphighiales); however free styles andany degree of apocarpy are never present in extant Rhizophoraceae. Extant genera ofResedaceae are herbs to subshrubs that occur in dry mediterranean climates and disturbedsandy habitats in contrast to the paleoenvironmental reconstructions of meandering riversystems. However, some Resedaceae are weedy generalists. These flowers represent theonly fossil record and the only South American occurrence for this mainly NorthernHemisphere family, providing an important temporal and geographic calibration forResedaceae and Brassicales.