Dunn, Michael T .
Tetrastichia bupatides Gordon and a Possible Relationship with the Medullosaceae.
Tetrastichia bupatides was first described by Gordon (1938) and ranges from the late Famennian of Ireland to the late Tournaisian of Oxroad Bay, Scotland. As originally diagnosed, these stems form a cruciform protostele with an occasional fifth lobe. Protoxylem maturation is mesarch and protoxylem poles are located near the center and apices of each lobe. Secondary growth is known only from loose wood produced by older stems: vascular cambium, phloem and periderm have not been observed. Inner cortex consists of thin walled parenchyma with sclerotic clusters often located between the lobes of the stele. Outer cortex ranges from anastomosing to parallel bands of sclerenchyma. Phyllotaxy is opposite decussate with leaf traces forming at the ends of each lobe producing Lyginorachis- type petioles that bifurcate repeatedly. New information on this genus comes from additional material collected from the Oxroad Bay locality by R. M. Bateman and G. W. Rothwell. These new data suggest adventitious roots are often produced just below the first bifurcation and that the presence or absence of secondary growth is due to taphonomy rather than ontogeny. In addition, a number of characters exhibit a range of variation within this population. For example the number of protostele lobes ranges from three to five, both Lyginorachis and Kalymma -type rachis bases are produced, discrete vascular segments are sometimes formed from the stelar lobes, and rachis bases can be vascularized by the usual single strand with abaxial corrugations or by discrete traces produced over the course of several millimeters. These latter two characters suggest a possible relationship with the Medullosaceae.
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1 - Cameron University, Department of Biological Sciences, Science Complex, Lawton, Oklahoma, 73505, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 11:00 AM