Poster

         Systematics

Fruits of Burseraceae—diagnostic traits and their recognition in the fossil record.

Presenting Author
Steven Manchester
Description
Although the drupe-like fruits of Burseraceae are not particularly distinctive when observed with their mesocarp and exocarp intact, the woody pyrenes within them display distinctive morphology that can allow for recognizing the family and for the distinction of potential clades at generic and/or intrageneric levels.  We surveyed pyrene morphology and locule configuration for species representing most extant genera of the family using micro-CT scanning to provide a framework for interpreting fossil pyrenes and locule casts.  Typically the fruits develop from an ovary of three to five carpels, but in some genera only one carpel develops fully resulting in a single unilocular fertile pyrene (e.g., Bursera, Commiphora), while in others all five (Garuga, Aucommea) or all three (Canarium) carpels may form pyrenes at maturity.  In most genera the pyrenes are readily separable from one another, but in Canarium and Trattinnickia the pyrenes are mutually fused.  Abortive pyrenes are obvious in Bursera, Commiphora and Santiria, remaining attached to the ventral surface of the larger, developed carpel.  Bursera and Commiphora pyrenes are typically thick-walled, whereas Dacryoides, Crepidospermum, Tetragastris and most Protium species have thin-walled pyrenes.  Similar observations of fossil specimens allow us to trace the Burseraceae back to the latest Cretaceous and early Paleocene of India.  The pentacarpellate fruit of Sahnianthus from the late Maastrichtian Deccan Intertrappean beds of central India shows five triangular pyrenes, hypogynous perianth, axial placentation, with mesocarp and exocarp opening septicically as valves exposing the pyrenes.  Burseraceous pyrenes and locule casts are well represented in the Eocene of North America and Europe indicating that the family was  more widely distributed at middle northern latitudes during warmer times.