Anatomy and Morphology of Araucaria sphaerocarpa Carruthers from the Jurassic Inferior Oolite of Bruton, Somerset

Abstract

Anatomical study of the holotype of the ovulate cone A. sphaerocarpa Carruthers reveals excellently preserved cone and seed tissues in spite of the fragmentary nature of the fossil remains. Large cone-scale complexes up to 4 cm long are helically arranged in the 13 .times. 15-cm cone. A ligular sulcus separates the strongly vascularized bract and scale. The pith of the cone axis is wide, and traces to the bract and scale diverge separately from the axis stele. One large inverted ovule is embedded in the tissue of each ovuliferous scale. The integuments are well developed, with slight lateral extensions. The wide band of elongate sclereids in the stony layer, has a zigzag pattern in surface view. The nucellus, attached only at the chalazal end of the inner integumentary layer, does not appear to have the wavy apex characteristic of other araucarians. Thin-walled, isodiametric megagametophyte cells surround large, well-developed embryos that have 2 cotyledons. The cone structure most closely resembles that of A. bidwillii Hooker, section Bunya. The occurrence of the fossil in England extends the range of this section to the Northern Hemisphere during the Jurassic.